DATE: 7/29/99. PAGE: 1 of 32

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1 UI BULLETIN # 24 SUBJECT: Engine Speed Control for 7.4L (LP4/L21) Gas Engines MODELS AFFECTED: C-Series Trucks MODEL YEAR(S): 1999/2000 DATE: 7/29/99 PAGE: 1 of 32 The purpose of this bulletin is to provide Upfitters and Special Vehicle Manufactures (SVMs) with information regarding the Fast Idle (UF3) and Power Take Off (PTO) options. This bulletin also provides installation instructions for interface with the Remote PTO connector. If you have any questions please call the Upfitter Intergration Hotline at TABLE OF CONTENTS Overview Pages2-3 Fast Idle (UF3) Description and Operation Pages4-6 Power Take Off (PTO) Modes and Switches Page 7 PTO -Stationary Preset Mode Pages8-12 PTO - Stationary Variable Mode Pages13-16 PTO-Mobile Variable Mode Pages17-20 PTO Engine Fault Shutdown Page 21 Remote PTO Connector Page 21 Appendix-Reprogramming the PCM for Fast Idle/PTO Pages22-23 Using the Tech 2 Scan Tool Illustrations Pages24-32

2 OVERVIEW I. PTO A Power Take Off (PTO) is a gearbox or mechanical device used to transmit mechanical power from the powertrain, through gears or a transmission, to another mechanical or hydraulic device. Examples of PTO applications are: salt spreaders, refuse equipment, plows, pumps, wrecker equipment, dump bodies, fire/rescue equipment, etc. ADVANTAGES OF PTOs PTOs are inexpensive, convenient, safe and reliable. PTOs bolt onto transmissions, engines, transfer cases or can be incorporated into the accessory drive belt system. PTOs eliminate the need for a complex array of levers, controllers, electric motors, etc., that would be required to duplicate the operation of a PTO. High idle refers to the increase of engine RPMs to values higher than normal base idle. High idle historically has been provided through additional mechanical hardware to regulate an increased engine RPM rating. Today, an increasing number of engines have high idle operation provided through switches, circuits and the programming of the Powertrain Control Module (PCM). The GM PTO option provides various high idle controls to aid in the operation of a PTO. The GM Fast Idle (UF3) option also provides high idle control but only to one setting and is not typically used to operate a PTO. The UF3 option is used for quick warm up on cold days, charging of batteries or to increase A/C performance. II. PTO OPERATION ON THE VORTEC 7400MD 7.4L GAS ENGINE (LP4/L21) In the 1999 model year, the Vortec 7400MD engines are offered as the gas engines for the Medium Duty C-Series trucks. The LP4 engine (210 HP) replaces the baseline LSO (6.0L) engine. The L21 engine (270 HP) replaces the up-option LRO (7.0L) engine. The LP4/L21 engines differ from their predecessors is that they incorporate an electronically controlled throttle verses a mechanically controlled throttle. Various engine functions, including idle, are now controlled through electronic means. The purpose of the electonically controlled throttle is to meet customer requirements for Power Management, Engine and Vehicle Speed Governing and PTO control. RB/ML Bulletin /04/99

3 The Electronic Throttle Control (ETC) system consists of three components: Accelerator Pedal Module Throttle Air Control Body Throttle Actuator Control Module These components are linked to the Powertrain Control Module (PCM). The PCM receives information from engine inputs (temperature, speed, air flow, etc.) and vehicle inputs (PTO request, cruise requests, vehicle speed, etc.) and the accelerator pedal position. These functions determine and then control the desired engine air flow. To obtain high idle control on the LSO and LRO engines, the upfitter/svm would need to adjust the mechanical throttle linkage to set the desired engine speed. On the LP4/L21 engines, high idle is controlled through electronic means. A number of provisions have been made on the 1999 C-Series trucks with the LP4/L21 engines to aid in high idle control. There are two RPO codes associated with high idle functions. There is also a Remote PTO Connector added for remote switch interfacing into the high idle control circuits. The RPO codes which apply to high idle control on the LP4/L21 engines are: UF3 (Fast Idle switch) PTO (Provisions - Power Take Off Control) The above options will be described in detail in the next section of this bulletin. Also, please note that this bulletin is only intended to address electronic aspects of high idle control. Other PTO related RPOs such as V66 (Mechanical Provisions for Front PTO) which may be considered by the customer, are not addressed here. The parameters on the Fast Idle (UF3) and the Power Take Off (PTO) options can be programmed into the PCM with a GM Tech 2 scan tool (see Appendix page 22). The GM Tech 2 scan tool connects to the datalink connector under the dash above the driver s footwell area. A GM dealership will be able to perform this programming. Companies that wish to own a Tech 2 tool can obtain more information by calling GM-TOOLS. RB/ML Bulletin /04/99

4 FAST IDLE (UF3) I. DESCRIPTION Vehicles ordered with UF3 (Fast Idle) will come equipped with a dash mounted switch which will allow the user to increase the engine idle to a preset engine speed. The factory preset for Fast Idle is 1200 RPM but this parameter can be reprogrammed as described in the Appendix. The Fast Idle switch is located on the dash panel to the left of the steering column as shown on the Fast Idle Switch illustration (page 24). The telltale which indicates fast idle operation is located next to the switch (page 25). The fast idle feature can only be used when the vehicle is stationary. UF3 is available as a Regular Production Option (RPO) on C-Series trucks and is mutually exclusive from the PTO RPO. PROGRAMMABLE PARAMETERS FACTORY SETTINGS (RPM) MINIMUM VALUE (RPM) MAXIMUM VALUE (RPM) Maximum Fast Idle Speed (See Note Page 6) Base Fast Idle Speed Cannot be set below Base Fast Idle Speed Parameters. Although programmable to 3800 RPM, the engine governor limits engine speed to 3750 RPM Normal engine idle will override if higher than requested PTO base idle. Cannot be set above the Maximum Fast Idle Speed Parameter. Note: The values shown in the above chart although accurate at time of bulletin publication, may change in time due to various reasons including running changes made to the PCM, calibrations, Tech 2 programming software, etc. RB/ML Bulletin /04/99

5 FAST IDLE (UF3) - Continued II. HOW TO OPERATE To enable Fast Idle, the following conditions must be met: 1. Engine must be running 2. Transmission must be in PARK or NEUTRAL 3. Vehicle speed must be zero. 4. Brake or Clutch must not be depressed. 5. CHECK ENGINE lamp must not be illuminated. When the above conditions are met, the operator can then activate the Fast Idle mode by depressing the Fast Idle switch. If the switch is depressed while the engine is in Fast Idle mode, the engine will return to normal base idle. Any changes to these conditions will result in the engine returning to normal base idle. III. ADJUSTING THE FACTORY PRESET ENGINE SPEED The Base Fast Idle Speed parameter is factory preset to 1200 RPM. This parameter is programmable in 50 RPM increments within the range of 600 RPM to 1300 RPM. If normal engine idle is higher than the requested high idle, the normal engine idle will override. The Maximum Fast Idle Speed parameter is factory preset to 2500 RPM. This parameter is programmable in 50 RPM increments within the range of 1000 RPM or the Base Fast Idle Speed (whichever is higher) to 3800 RPM. The above parameters can be reprogrammed with a GM Tech 2 diagnostic scan tool. The Tech 2 connects to the Data Link Connector under the dash. Information regarding reprogramming with the Tech 2 tool can be found in the Appendix (page 22). IV. ILLUSTRATIONS 1. FAST IDLE SWITCH page FAST IDLE LAMP page 25 RB/ML Bulletin /04/99

6 NOTE: Maximum Fast Idle Speed FAST IDLE (UF3) - (Continued) The Maximum Fast Idle Speed is the RPM setting above which the Fast Idle Mode will be disabled. This is NOT the maximum RPM value the engine would obtain by depressing the Fast Idle Switch. For example, if all Fast Idle Mode enable criteria are met, the Base Fast Idle Speed is programmed to 1200 RPMs and the Maximum Fast Idle Speed is programmed to 2000 RPMs, the engine speed will only increase to 1200 RPMs by depressing the Fast Idle Switch. If the engine speed is increased to any speed less than 2000 RPMs by depressing the accelerator pedal, the engine speed will return 1200 RPMs upon releasing the accelerator pedal. However, if the engine speed is increased above 2000 RPMs by depressing the accelerator pedal, the Fast Idle Mode will be disabled and the engine speed will return to its normal base idle upon releasing the accelerator pedal. Once the Maximum Fast Idle Speed is reached, Fast Idle is disabled. The Maximum Fast Idle Speed value DOES NOT limit the accelerator pedal from exceeding this value, it only disables the Fast Idle Mode. The Maximum Fast Idle Speed should also be set RPMs higher than the Base Fast Idle Speed value to allow for engine speed overshoot due to various conditions. RB/ML Bulletin /04/99

7 POWER TAKE OFF (PTO) The PTO RPO is an option that allows the user to raise engine speed electronically through the use of designated switches and PCM programming. The Vortec 7400 MD engine can be programmed to one of the following three PTO high idle modes: Stationary Preset Three preset high idle speeds. Vehicle must be stationary. Stationary Variable Variable high idle speeds. Vehicle must be stationary. Mobile Variable Allows variable PTO speeds while vehicle is moving. These PTO modes are addressed separately and in detail in the following pages. Please note that the PCM can be programmed to only ONE of the three modes at any given time. PTO programming and parameters are addressed in the following pages. PTO WITH CRUISE PTO SWITCHES Depending on the options of the truck, different switches will be used for PTO operation. If the truck has PTO with cruise, the switches used are: Cruise ON/OFF PTO Enable Set/Coast (referred to as SET throughout the rest of the bulletin) Res/Accel (referred to as RES throughout the rest of the bulletin) If the truck has PTO without cruise or has been wired for remote PTO operation, the switches used are: PTO On/Off PTO Enable PTO Up (same function as RES) PTO Down (same function as SET) PTO SWITCH CONVERSION CHART PTO WITHOUT CRUISE REMOTE PTO WIRING CRUISE ON/OFF PTO ON/OFF PTO ON/OFF PTO ENABLE SET PTO ENABLE PTO DOWN PTO ENABLE PTO DOWN RES PTO UP PTO UP RB/ML Bulletin /04/99

8 PTO - STATIONARY PRESET MODE I. DESCRIPTION The Stationary Preset Mode of PTO allows the user to select from three high idle speeds which are programmed into the PCM. The user can toggle between THREE preset engine speeds through the use of the SET or RES switches (with cruise). See the PTO switch conversion chart (page 7) for other PTO wiring configurations. PROGRAMMABLE PARAMETERS FACTORY SETTING (RPM) MINIMUM VALUE (RPM) MAXIMUM VALUE (RPM) Maximum Fast Idle Speed (See Note Page 12) Base Fast Idle Speed Cannot be set below Base Fast Idle Speed Parameters Normal engine idle will override if higher than requested PTO base idle. Although programmable to 3800 RPM, the engine governor limits engine speed to 3750 RPM. Cannot be set above the Maximum Fast Idle Speed Parameter. Base Fast Idle Speed (Set) Cannot be set below Base Fast Idle Speed Parameters. Maximum Fast Idle Speed Base Fast Idle Speed (Res) Maximum Fast Idle Speed Cannot be set below Base Fast Idle Speed Parameters. Note: The values shown in the above chart although accurate at time of bulletin publication, may change in time due to various reasons including running changes made to the PCM, calibrations, Tech 2 programming software, etc. RB/ML Bulletin /04/99

9 II. HOW TO OPERATE PTO - STATIONARY PRESET MODE (Continued) Prior to enabling the Stationary Preset Mode, the following conditions must be met: 1. Engine must be running 2. Transmission must be in PARK or NEUTRAL 3. Vehicle speed must be zero 4. Brake or clutch must not be depressed 5. CHECK ENGINE lamp must not be illuminated NOTE: The PCM requires that the brake or clutch pedal be depressed at some point during or after engine start up before allowing the PTO mode to be enabled. Once the above conditions have been met, the user may proceed to one of the following sequences to activate the PTO high idle mode. 1. Set Cruise On/Off Switch to On position. 2. Set PTO Enable Switch to On position. PRIMARY SEQUENCE Upon completion of the above steps, the PTO Stationary Preset mode will be enabled and the engine speed will increase to the Base Fast Idle Speed. The Switch Operation Chart on the next page describes how to toggle between the preset high idle speeds. 1. Set PTO Enable Switch to On position. 2. Set Cruise On/Off Switch to On position. 3. Press either the SET or RES switch. ALTERNATE SEQUENCE When this sequence is followed, engine speed will jump from normal idle to either the Fast Idle Speed (SET) or Fast Idle Speed (RES) depending on which switch is pressed first. The Switch Operation Chart on the next page describes how to toggle between the preset high idle speeds. Any changes in the above conditions, including the depressing of brake or clutch pedals, will disable the Stationary Preset Mode causing the engine to return to normal base idle. Also, usage of the accelerator pedal to raise the engine idle above the Maximum Fast Idle Speed will result in the disabling of the PTO Stationary Preset Mode. RB/ML Bulletin /04/99

10 PTO - STATIONARY PRESET MODE (Continued) The following chart shows how to toggle between the THREE different engine speeds through the SET and RES switches. PTO STATIONARY PRESET MODE Switch Operation Chart PRESENT PTO STATE PRESSING RESULTING PTO STATE BASE FAST IDLE SPEED (Factory set 1200 RPM) BASE FAST IDLE SPEED (Factory set 1200 RPM) FAST IDLE SPEED (SET) (Factory set 1400 RPM) FAST IDLE SPEED (SET) (Factory set 1400 RPM) FAST IDLE SPEED (RES) (Factory set 1800 RPM) FAST IDLE SPEED (RES) (Factory set 1800 RPM) SET RES SET RES SET RES FAST IDLE SPEED (SET) (Factory set 1400 RPM) FAST IDLE SPEED (RES) (Factory set 1800 RPM) BASE FAST IDLE SPEED (Factory set 1200 RPM) FAST IDLE SPEED (RES) (Factory set 1800 RPM) FAST IDLE SPEED (SET) (Factory set 1400 RPM) BASE FAST IDLE SPEED (Factory set 1200 RPM) RB/ML Bulletin /04/99

11 PTO - STATIONARY PRESET MODE (Continued) III. ADJUSTING THE FACTORY PRESET ENGINE SPEED The Base Fast Idle Speed parameter is factory preset to 1200 RPM. This parameter is programmable in 50 RPM increments within the range of 600 RPM to 1300 RPM. If normal engine idle is higher than the requested high idle, the normal engine idle will override. The Maximum Fast Idle Speed parameter is factory preset to 2500 RPM. This parameter is programmable in 50 RPM increments within the range of 1000 RPM or the Base Fast Idle Speed (which ever is higher) to 3800 RPM. The Fast Idle Speed (SET) parameter is factory preset to 1400 RPM. This parameter is programmable in 50 RPM increments within the range of 1000 RPM to Maximum High Idle Speed. The Fast Idle Speed (RES) parameter is factory preset to 1800 RPM. This parameter is programmable in 50 RPM increments within the range of 1000 RPM to Maximum High Idle Speed. The Fast Idle Speed (RES) value must be greater than the Fast Idle Speed (SET) value. The parameters can be reprogrammed with a GM Tech 2 diagnostic scan tool. The Tech 2 connects to the Data Link Connector under the dash. Information regarding reprogramming with the Tech 2 tool can be found in the Appendix page 22. IV. ILLUSTRATIONS LOCATION VIEW OF PTO ENABLE SWITCH page 26 LOCATION VIEW OF REMOTE PTO CONNECTOR page /2000 C-SERIES REMOTE PTO CONNECTOR pages 28,29 BODY BUILDER WIRING REQUIRED page 30 REMOTE PTO OPERATION SCHEMATIC page 31,32 RB/ML Bulletin /04/99

12 NOTE: Maximum Fast Idle Speed PTO - STATIONARY PRESET MODE (Continued) The Maximum Fast Idle Speed is the RPM setting above which the PTO Stationary Preset Mode will be disabled. This is NOT the maximum RPM value the engine would obtain by depressing the SET or RES switches. For example, if all PTO Stationary Preset Mode enable criteria are met, the Fast Idle Speed (SET) is programmed to 1400 RPMs and the Maximum Fast Idle Speed is programmed to 2000 RPMs, the engine speed will only increase to 1400 RPMs by depressing the SET switch. If the engine speed is increased to any speed less than 2000 RPMs by depressing the accelerator pedal, the engine speed will return 1400 RPMs upon releasing the accelerator pedal. However, if the engine speed is increased above 2000 RPMs by depressing the accelerator pedal, the PTO Stationary Preset Mode will be disabled and the engine speed will return to its normal base idle upon releasing the accelerator pedal. Once the Maximum Fast Idle Speed is reached, the PTO Stationary Preset Mode is disabled. The Maximum Fast Idle Speed value DOES NOT limit the accelerator pedal from exceeding this value, it only disables the PTO Stationary Preset Mode. The Maximum Fast Idle Speed should also be set RPMs higher than the maximum setting that will be used to allow for engine speed overshoot due to various conditions. RB/ML Bulletin /04/99

13 PTO - STATIONARY VARIABLE MODE I. DESCRIPTION The Variable Stationary Preset Mode of PTO allows the customer to retain engine speed at a desired value through the use of the accelerator pedal and the SET or RES switches. The engine speed selected must be greater than the Base Fast Idle Speed value and lower than the Maximum Fast Idle Speed value. The chart below lists the programmable parameters. PROGRAMMABLE PARAMETERS FACTORY SETTING (RPM) MINIMUM VALUE (RPM) MAXIMUM VALUE (RPM) Maximum Fast Idle Speed (See Note Page 16) Base Fast Idle Speed Cannot be set below base fast idle speed parameter. 600 Normal engine idle will override if higher than requested PTO Base Idle. Although programmable to 3800 RPM, the engine governor limits engine speed to 3750 RPM Cannot be set above the maximum fast idle speed parameter Note: The values shown in the above chart although accurate at time of bulletin publication, may change in time due to various reasons including running changes made to the PCM, calibrations, Tech 2 programming software, etc. RB/ML Bulletin /04/99

14 11. HOW TO OPERATE PTO - STATIONARY VARIABLE MODE (Continued) To engage the PTO Stationary Variable Mode the following conditions must be met: 1. Engine must be running 2. Transmission must be in PARK or NEUTRAL 3. Vehicle speed must be zero. 4. Brake or clutch must not be depressed. 5. CHECK ENGINE lamp must be illuminated. NOTE:The PCM requires that the brake or clutch pedal be depressed at some point during or after engine start up before allowing the PTO mode to be enabled. Once the above conditions have been met, the user may proceed to one of the following sequences to activate the PTO high idle mode. 1. Set Cruise On/Off Switch to On position. 2. Set PTO Enable Switch to On position. PRIMARY SEQUENCE Upon completion of the above steps, the PTO Stationary Preset Mode will be enabled. The engine speed will increase to the Base Fast Idle Speed. The PTO Stationary Variable Function Mode Chart on the next page describes how to increase or decrease the idle speed. ALTERNATE SEQUENCE 1. Set PTO Enable Switch to On position. 2. Set Cruise On/Off Switch to On position. 3. Depress accelerator pedal to obtain desired high idle speed. 4. Press SET button to hold engine at desired high idle speed. The SET and RES switches can then be used to adjust the engine speed in 25 RPM increments. See the PTO - Stationary Variable Mode Function Chart (page 15)for details of operation. Any changes in the above conditions, including the depressing of brake or clutch pedals, will disable the PTO Stationary Variable Mode causing the engine to return to normal base idle. Also, usage of the accelerator pedal to raise the engine idle above the Maximum Fast Idle Speed will result in the disabling ofthe PTO Stationary Variable Mode. RB/ML Bulletin /04/99

15 PTO - STATIONARY VARIABLE MODE (Continued) PTO - STATIONARY VARIABLE MODE FUNCTION CHART SWITCH SET RES PRESSING ONCE HELD Engine speed will decrease by 25 RPM decrements and will maintain new engine speed value. Engine speed can be decreased down to engine base idle speed value. If engine speed is at the engine base idle speed value, all set inputs will be ignored. Decelerates engine down to the engine base idle speed value. Engine speed will increase by 25 RPM increments and will maintain new engine speed value. Engine speed can be increased up to the maximum fast idle speed value. If engine speed is at the maximum fast idle speed value, all res inputs will be ignored. Increases engine speed up to the maximum fast idle speed value. NOTE: If the Stationary Variable Mode is disabled (i.e., brake was depressed), it may be re-enabled by pressing the RES switch. This will cause the engine to resume to the speed it was at prior to disabling. III. ADJUSTING THE FACTORY PRESET ENGINE SPEED The Base Fast Idle Speed parameter is factory preset to 1200 RPM. This parameter is programmable in 50 RPM increments within the range of 600 RPM to 1300 RPM. If normal engine idle is higher than the requested High Idle, the normal engine idle with override. The Maximum Fast Idle Speed parameter is factory preset to 2500 RPM. This parameter is programmable in 50 RPM increments within the range of 1000 RPM or the Base Fast Idle Speed (whichever is higher) to 3800 RPM. The parameters can be reprogrammed with a GM Tech 2 diagnostic scan tool. The Tech 2 connects to the Data Link Connector under the dash. Information regarding reprogramming with the Tech 2 tool can be found in the Appendix page 22. IV. ILLUSTRATIONS LOCATION VIEW OF PTO ENABLE SWITCH page 26 LOCATION VIEW OF REMOTE PTO CONNECTOR page /2000 C-SERIES REMOTE PTO CONNECTOR pages 28,29 BODY BUILDER WIRING REQUIRED page 30 REMOTE PTO OPERATION SCHEMATIC page 31,32 RB/ML Bulletin /04/99

16 NOTE: Maximum Fast Idle Speed PTO - STATIONARY VARIABLE MODE (Continued) The Maximum Fast Idle Speed is the RPM setting above which the PTO Stationary Variable Mode will be disabled. For example, the PTO Stationary Variable Mode is enabled, the current engine speed is 1400 RPMs and the Maximum Fast Idle Speed is programmed to 2000 RPMs. If the engine speed is increased to any speed less than 2000 RPMs by depressing the accelerator pedal, the engine speed will return to 1400 RPMs upon releasing the accelerator pedal. However, if the engine speed is increased above 2000 RPMs by depressing the accelerator pedal, the PTO Stationary Variable Mode will be disabled and the engine speed will return to its normal base idle upon releasing the accelerator pedal. Once the Maximum Fast Idle Speed is reached through the use of the accelerator pedal or PTO switches, the PTO Stationary Variable Mode is disabled. However, the Maximum Fast Idle Speed value DOES NOT limit the accelerator pedal from exceeding this value, it only disables the PTO Stationary Variable Mode. RB/ML Bulletin /04/99

17 PTO - MOBILE VARIABLE MODE I. DESCRIPTION The PTO Mobile Variable Mode allows the driver to maintain a desired engine speed (not vehicle speed) while the vehicle is moving. With a manual transmission this mode is used with the vehicle in gear. This feature will soon be released for automatic transmissions. The engine speed (RPM) selected must be greater than the Base Fast Idle Speed value and lower than the Maximum Fast Idle Speed value. The vehicle speed must between the Minimum and Maximum Vehicle Speed Values. The engine and vehicle speed default parameters are as follows: PROGRAMMABLE PARAMETERS FACTORY SETTING MINIMUM VALUE MAXIMUM VALUE Maximum Fast Idle Speed (See Note Page 20) Base Fast Idle Speed Maximum Vehicle Speed 2500 RPM 1000 RPM Cannot be set below Base Fast Idle Speed Parameters. Normal engine idle will override if higher than requested PTO base idle RPM Although programmable to 3800 RPM, the engine governor limits engine speed to 3750 RPM RPM RPM 20 MPH 32 KPH 3 MPH Cannot be set above the Maximum Fast Idle Speed Parameter. 30 MPH 5 KPH 48 KPH Note: The values shown in the above chart although accurate at time of bulletin publication, may change in time due to various reasons including running changes made to the PCM, calibrations, Tech 2 programming software, etc. RB/ML Bulletin /04/99

18 PTO - MOBILE VARIABLE MODE (Continued) II. HOW TO OPERATE To engage the PTO Mobile Variable Mode the following conditions must be met in the following order: 1. Engine must be running 2. Transmission must be in gear 3. Vehicle must be traveling between 3 MPH and the Maximum Vehicle Speed setting 4. Brake or clutch must not be depressed 5. CHECK ENGINE lamp must not be illuminated 6. PTO Enable switch must be set to On position When the above conditions are met, the operator can then activate the Mobile Variable Mode by using the accelerator to adjust the engine RPM to a desired value then pressing the SET button to set the engine speed. The SET and RES switches can then be used to adjust the engine speed in 25 RPM increments. See the PTO - Mobile Variable Mode Function Chart for details of operation. Any changes in the above conditions including the depressing of brake pedal, clutch pedal, raising engine speed above the Maximum Fast Idle Speed, or lowering vehicle speed below 3 MPH, will result in the disabling of the PTO Mobile Variable Mode. NOTE: If the Mobile Variable Mode is disabled (i.e., brake was depressed), it may be re-enabled by pressing the RES switch. This will cause the engine to resume to the speed it was at prior to disabling. RB/ML Bulletin /04/99

19 PTO - MOBILE VARIABLE MODE (Continued) PTO - MOBILE VARIABLE MODE FUNCTION CHART SWITCH PRESSING ONCE HELD SET Engine speed will decrease by 25 RPM decrements and will maintain new engine speed value. Engine speed can be decreased down to engine base idle speed value. If engine speed is at the engine base idle speed value, all set inputs will be ignored. If the vehicle reaches 3 MPM, the PTO mode will be disengaged. Decelerates engine down to the engine base idle speed value. If the vehicle reaches 3 MPH, the PTO mode will disengage. RES Engine speed will increase by 25 RPM increments and will maintain new engine speed value. Engine speed can be increased to maximum fast idle speed value. If engine speed is at the maximum fast idle speed value, all res inputs will be ignored. If the vehicle reaches the Maximum Vehicle Speed value, PTO will be disengaged. Increases engine speed up to the maximum fast idle speed value. If the vehicle reaches the Maximum vehicle speed value, PTO will be disengaged. III. ADJUSTING THE FACTORY PRESET ENGINE SPEED The Base Fast Idle Speed parameter is factory preset to 1200 RPM. This parameter is programmable in 50 RPM increments within the range of 600 RPM to 1300 RPM. If normal engine idle is higher than the requested high idle, the normal engine idle will override. The Maximum Fast Idle Speed parameter is factory preset to 2500 RPM. This parameter is programmable in 50 RPM increments within the range of 1000 RPM or the Base Fast Idle Speed (whichever is higher) to 3800 RPM. The Maximum Vehicle Speed parameter is factory preset to 20 MPH. This parameter is programmable within the range of 3 MPH to 30 MPH. The parameters can be reprogrammed with a GM Tech 2 diagnostic scan tool. The Tech 2 connects to the Data Link Connector under the dash. Information regarding reprogramming with the Tech 2 tool can be found in the Appendix (page 22). IV. ILLUSTRATIONS - LOCATION VIEW OF PTO ENABLE SWITCH page 26 RB/ML Bulletin /04/99

20 NOTE: Maximum Fast Idle Speed PTO - MOBILE VARIABLE MODE (Continued) The Maximum Fast Idle Speed is the RPM setting above which the PTO Mobile Variable Mode will be disabled. For example, the PTO Mobile Variable Mode is enabled, and the current engine speed is1400 RPMs and the Maximum Fast Idle Speed is programmed to 2000 RPMs. If the engine speed is increased to any speed less than 2000 RPMs by depressing the accelerator pedal, the engine speed will return to 1400 RPMs upon releasing the accelerator pedal. However, if the engine speed is increased above 2000 RPMs by depressing the accelerator pedal, the PTO Mobile Variable Mode will be disabled and the engine speed will return to its normal base idle upon releasing the accelerator pedal. Once the Maximum Fast Idle Speed is reached through the use of the accelerator pedal or PTO switches, the PTO Mobile Variable Mode is disabled. The Maximum Fast Idle Speed value DOES NOT limit the accelerator pedal from exceeding this value, it only disables the PTO Mobile Variable Mode. RB/ML Bulletin /04/99

21 PTO ENGINE FAULT SHUTDOWN The PTO option includes provisions for PTO engine fault shutdown. This feature allows the operator to kill the engine while in the PTO mode through an aftermarket installed switch. If the truck is NOT in the PTO mode, the pressing of the switch will have no effect on engine operation. To install this feature, a toggle switch must be connected to terminals H (Light Blue Wire) and A (Black White Wire) of the Remote PTO connector (see pages 30,32). Important: If the PTO Engine Shut Down feature is to be used, it must be turned on in the PCM. If this feature is not turned on, the switch will have no effect on the engine. The Appendix (page 22) of this bulletin shows how to use the Tech 2 scan tool to reprogram the PCM. REMOTE PTO CONNECTOR The Remote PTO Connector [located in the right side of the engine compartment near the right wheel (page 27)] has been provided to allow for the installation of remote PTO idle controls. The upfitter can access the PTO high idle circuits through this connector. To use the Remote PTO connector, the upfitter must provide the mating connector, wiring, and remote switches. Two momentary switches are required to duplicate the operation of the SET and RES switches in the cab. These switches will be connected to the Remote PTO Connector shown on pages (28,29). The schematics showing the switches can be found on pages The PTO Up switch duplicates the RES switch operation and the PTO Down switch duplicates the SET switch operation. Please note that PTO high idle must still be enabled from the Cruise ON/OFF and the PTO Enable switches within the cab. The PTO Engine Fault Shut Down feature (optional) can also be accessed through this connector (pages 30,32). One toggle switch is used for the PTO Engine Shut Down feature if it is desired. Important: If the PTO Engine Shut Down feature is to be used, it must be turned on in the PCM. If this feature is not turned on, the switch will have no effect on the engine. ILLUSTRATIONS LOCATION VIEW OF REMOTE PTO CONNECTOR page /2000 C-SERIES REMOTE PTO CONNECTOR pages 28,29 BODY BUILDER WIRING REQUIRED page 30 REMOTE PTO OPERATION SCHEMATIC page 31,32 RB/ML Bulletin /04/99

22 APPENDIX REPROGRAMMING THE PCM FOR FAST IDLE/PTO USING THE TECH 2 SCAN TOOL The Tech 2 scan tool MUST be used to enable the Fast Idle and PTO options and adjust the factory preset parameters to desired settings. The Tech 2 menu driven device is a hand held scan tool that plugs into the datalink connector located underneath the dash near the driver s seat. Once the Tech 2 is connected, the following chart will guide the user. STEP CURRENT MENU MAIN VEHICLE IDENTIFICATION VEHICLE IDENTIFICATION SYSTEM SELECTION VEHICLE IDENTIFICATION VEHICLE IDENTIFICATION POWERTRAIN SPECIAL FUNCTIONS CURRENT PTO SETTINGS PTO OPTIONS SELECT F0: DIAGNOSTICS YEAR OF VEHICLE MEDIUM DUTY TRUCK F0: POWERTRAIN LP4 OR L21 AUTOMATIC OR MANUAL F2: SPECIAL FUCNTIONS F3: PTO OPTIONS CHANGE OPTIONS SEE PAGE 23 RB/ML Bulletin /04/99

23 APPENDIX (Continued) REPROGRAMMING THE PCM FOR FAST IDLE/PTO USING THE TECH 2 SCAN TOOL TO ADJUST THE MODE OF OPERATION: The PTO OPTIONS MENU will appear with the selections: FO: FAST IDLE F1: STATIONARY PRESET FAST IDLE F2: STATIONARY VARIABLE FAST IDLE F3: MOBILE VARIABLE FAST IDLE Once the mode of operation is selected the CURRENT PTO SETTINGS menu will appear with the adjustable parameters for the current mode. This screen allows the user to increase or decrease engine RPM values using the INCREASE and DECREASE buttons. If the Engine Fault Shutdown feature is selected, the YES or NO buttons will determine if this feature is enabled. After all the settings are adjusted, the user will press the REPROGRAM button and the CURRENT PTO SETTINGS menu will appear with the changes. The ignition must be turned off for ten seconds to ensure that the program values are stored in the PCM. SERVICE CONSIDERATIONS IMPORTANT: Please be aware that UF3 and PTO high idle settings must be reprogrammed in the event that the PCM is replaced. It may be advisable to provide the PCM settings information to the customer in case the PCM requires servicing during some point in the life of the vehicle. RB/ML Bulletin /04/99

24 FAST IDLE (UF3) FAST IDLE SWITCH FAST IDLE SWITCH PART # RB/ML Bulletin /04/99

25 FAST IDLE (UF3) FAST IDLE LAMP FAST IDLE LAMP PART # RB/ML Bulletin /04/99

26 LOCATION VIEW OF PTO ENABLE SWITCH PTO ENABLE SWITCH PART # RB/ML Bulletin /04/99

27 LOCATION VIEW OF REMOTE PTO CONNECTOR (LOCATED IN RIGHT SIDE OF ENGINE COMPARTMENT NEAR WHEEL) RELAY BRACKET DASH PANEL ENGINE HARNESS REMOTE PTO CONNECTOR PART # STARTER RELAY RB/ML Bulletin /04/99

28 1999/2000 C-SERIES REMOTE PTO CONNECTOR MATING CONNECTOR CONNECTOR ON HARNESS RB/ML Bulletin /04/99

29 1999/2000 C-SERIES REMOTE PTO CONNECTOR PART # (F) PART # (M) PIN WIRE FUNCTION A B C D E F G H 451 BLK/WT 87 GRY/BLK 84 DK/BLU 488 LT/GRN X X X 494 LT/BLU PCM GROUND CRUISE CONTROL RES/ACC SWITCH SIGNAL CRUISE CONTROL SET/COAST SWITCH SIGNAL PTO ENABLE SIGNAL NOT USED NOT USED NOT USED NOT USED RB/ML Bulletin /04/99

30 RB/ML Bulletin /04/99

31 RB/ML Bulletin /04/99

32 RB/ML Bulletin /04/99