Welcome back. In the next two

The Shock of Your Life, PART 2 OF 3 by Steve Garrett Welcome back. In the next two parts of this series, we ll look at how the Parallel Hybrid Truck (PHT) operates, and some of the procedures and precautions you should be aware of when servicing a Hybrid vehicle. As we discussed previously, the PHT was introduced as an option on the 2004 C/K truck platform. The primary functions of the system are to improve fuel economy, reduce emissions, and improve vehicle versatility. The fuel economy and emissions are improved by shutting off fuel delivery during coast/deceleration and when the vehicle is stopped or moving at speeds of 10-13 mph (16-22 km/h) or less. When you release the brake pedal, the engine restarts automatically; you simply step on the accelerator pedal to drive away. Since the engine will restart automatically, the driver must pay attention when releasing the brake or the vehicle may appear to surge forward, even without pressing the accelerator. In addition to fuel economy gains, this system smoothes drive train vibrations, especially during downshifts and engine on/off cycles. The automatic engine stop feature is designed to shut the engine off during specific driving conditions. This feature may not function or may be disabled if any of these conditions occur: The outside temperature exceeds 95ºF (35ºC) and the climate control is in auto mode. The shift lever is in the N, R, M2 or M1 range. The battery pack state of charge is low. Tow-Haul mode has been selected. The transfer case is in 4- Low. The brake pedal has been released for longer than 3 seconds while in Park. APO (Auxiliary Power Outlet) requirements exceed 1kW. The hood isn t fully closed. APO (Auxiliary Power Outlet) System Another primary function of the PHT system is to provide AC power to outlets mounted in the truck bed and rear of the cabin. The outlets are rated at 2400 watts: 20 amps at 120V, 60 Hz AC. A ground-fault protection circuit is contained within the Starter Generator Control Module (SGCM). If a short occurs or if the current flow exceeds the rated amount, the SGCM will shut the circuit off while commanding the BCM and IPC to flash an overload message in the Driver Information Center. Make sure the grill area of the truck isn t obstructed, as the SGCM requires air flow to keep cool. To energize the system, the customer simply presses the normally-open, momentary contact switch mounted on the dash. The APO switch is fed 5 volts from the HCM (Hybrid Control Module). The APO switch signals the HCM, which then signals the SGCM via the data bus. This energizes the system if the correct parameters are met. The APO system is capable of operating in 2 different modes: Normal Mode: This mode is used while the vehicle is in any gear range and the engine is running, or if the vehicle is in auto stop mode and the vehicle is moving. Continuous Mode: This mode is used when the vehicle is in park and the engine is running. Continuous mode can be operated even if the key isn t in the ignition. If you hold the APO button down for longer than 2 seconds, the lamp next to the APO button will begin to flash. Now you can turn the key to lock while the lamp is flashing, and remove it from the ignition. With the ignition in the lock position, the lamp will stop flashing and will remain on with the engine running. The system will continue operating in continuous 4 GEARS November/December 2006

mode until you press the button. If the fuel level becomes low while operating in continuous mode, the Driver Information Center will display a Low Fuel message and the horn will sound every 5 seconds for up to 5 minutes. If the vehicle is left unattended for the full 5 minutes, the engine will shut down and the APO disabled. The APO system may also become disabled while in continuous mode when any of these conditions occur: Vehicle security is violated Engine oil pressure drops too low Engine overheats The ignition key is turned from the lock position The Hybrid system overheats A circuit fault occurs Auxiliary Transmission Pump A secondary electric fluid pump is mounted to the valve body to keep the transmission operational even if the engine isn t running. The pump is controlled by the HCM via a relay. To diagnose the pump and its circuit, two new DTCs were developed: P2796 and P2797. An updated internal wiring harness includes a connector for the secondary fluid pump. A checkball has been added to the valve body for secondary pump operation. The checkball will be called out as number 399 in the manual. Auxiliary Coolant Pump The auxiliary coolant pump is mounted in the engine compartment above the right side frame rail. This pump provides coolant flow through the heater core when the engine isn t running or when the heating system is unable reach the desired temperature when the engine s at idle or low RPM. The pump is controlled by the HCM via a relay. EHPS (Electro-Hydraulic Power Steering) The EHPS pump uses a new type fluid known as Pentosin fluid. The pump is controlled by the EHPS module. The amount of steering and brake assist is determined by: Ignition switch position PRNDL position VSS User demand, which is measured by the brake pedal position sensor and the hand wheel sensor The system has two modes of operation: Shutdown and Activation. System shutdown mode is activated when either of these conditions occurs: Vehicle is in park Hydraulic assist isn t needed for more than 3 minutes The system will exit shutdown mode if any of these conditions occur: Hand wheel position changes Vehicle speed is indicated Brake pedal is applied SGCM Cooling Fan and Coolant Pump Engine coolant is circulated through the Starter Generator Control Module (SGCM). There s also a fan (04) to provide additional cooling for the SGCM. The SGCM coolant pump is located on the right side of the engine, in front of the air cleaner. The SGCM controls the coolant pump via a relay. Inputs To operate the output devices, the systems processors require information from several input devices, including: Brake Pedal Position Brake Switch Accelerator Pedal Position (APP) System Hood Ajar Switch Auxiliary Power Outlet (APO) Switch Coolant Temperature (CTS) Crankshaft Cruise Control Switch Intake Air Temperature (IAT) Oil Pressure A/C Inside Air Temperature Transmission Inputs: PRNDL, PSM, TOSS, Tow-Haul Hand Wheel (Steering Wheel) GEARS November/December 2006 5

The Shock of Your Life, Part 2 of 3 The brake pedal position sensor provides the EHPS with the position of the brake pedal as well as the rate of pedal movement. Brake Pedal Position The brake pedal position sensor is an input to the Electro-Hydraulic Power Steering (EHPS) module. The sensor is monitored directly by the EHPS module via a 5V reference circuit supplied by the EHPS. The brake pedal position sensor provides the EHPS with the position of the brake pedal as well as the rate of pedal movement. This information is used to determine the amount of steering and brake assist required. Brake Switch The brake switch is an input to the PCM. The switch is normally open, and pulls the circuit low when you apply the brake pedal. The PCM communicates brake switch position to the EHPS module and Hybrid Control Module (HCM) via serial data. Brake switch input is used to help diagnose the brake pedal position sensor, and as an input for the auto start/stop feature. Accelerator Pedal Position (APP) System The APP system input comes from the APP sensor assembly. The APP sensors send voltage signals to the Throttle Actuator Control Module (TACM). The TACM communicates the accelerator position to the PCM and the HCM. The input is used to operate the auto start/ stop feature. Hood Ajar Switch The hood ajar switch is mounted in the radiator support area as part of the hood latch assembly. The switch uses a 6040-ohm resistor connected in parallel across the hood ajar switch and hood ajar reference circuits. A 750-ohm resistor is connected in series with the circuit. The HCM measures the voltage difference between the reference and signal circuits to determine the hood position. The hood ajar switch allows the HCM to determine whether the Hybrid system should be enabled or disabled. Auxiliary Power Output (APO) The APO switch is a normally-open, momentary contact switch mounted in the dash. The APO switch receives a 5-volt signal from the HCM. The HCM monitors the voltage drop across the circuit to determine the switch position. The switch contains two resistors to help identify system faults. When you press the switch, the APO system energizes; pressing the switch a second time de-energizes the APO system. Coolant Temperature (CTS) 6 GEARS November/December 2006

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The Shock of Your Life, Part 2 of 3 The coolant temperature sensor allows the PCM to monitor engine temperature. The PCM sends coolant temperature information to the HCM and the Starter Generator Control Module (SGCM). This information is used to disable APO operation if the engine overheats. Crankshaft The crank sensor is a Hall Effect sensor that sends a square wave signal to the PCM. The PCM converts the signal into 2X and 12X signals, which it sends directly to the SGCM over dedicated circuits. Cruise Control Switch The cruise control switch is an input to the Throttle Actuator Control Module (TACM). The TACM sends the cruise command status to the PCM, which relays the information to the HCM via serial data. Intake Air Temperature (IAT) The intake air temperature sensor is a direct input to the PCM. The PCM relays the information to the HCM. Oil Pressure The engine oil pressure sensor is an input to the PCM. The PCM relays the information to the HCM via serial data. The HCM uses the information to disable the APO system and to shut the engine off if the vehicle is being operated in continuous mode and oil pressure drops too low. A/C Pressure Located in the A/C high pressure line, the sensor sends a signal to the PCM regarding the status of the A/C high pressure system. This information is relayed to the HCM and is used to determine whether the auto stop feature should be allowed to function or not. Inside Air Temperature This information is measured by the in-car air temperature sensor located in the roof liner of the vehicle. This information is used to determine whether A/C operation is needed while the Hybrid system is operating. Transmission Inputs PRNDL Switch/PSM: The PRNDL switch and the PSM are inputs to the PCM and are used by the HCM to determine manual valve position. This information is used to determine the Hybrid mode of operation. TOSS: Transmission output shaft speed is an input to the PCM which is then relayed to the HCM. The HCM uses the data to determine vehicle speed for auto stop/start functions. Tow-Haul: The tow-haul feature is an input to the BCM which is then relayed to the PCM and HCM. The HCM uses the information to cancel the auto stop/start functions when tow-haul is selected. Engine Auto Start Mode: If the vehicle is in park, this message lets the driver know the engine could start at any time. Hand Wheel The hand wheel (steering wheel) sensor is part of the steering column. It contains two outputs: Phase A and Phase B. The two outputs are 90º out of phase from one another. The outputs provide square wave inputs to the EHPS module. The data received is used to determine the rate of steering wheel movement. This is used to determine the amount of power assist needed. Driver Information Center (DIC) Messages The driver information center is located on the left side of the instrument panel. The DIC will notify the customer regarding the status of the Hybrid system. If the system function is affected or a system fault is present, one of these messages will be displayed: 42V Switch Off: The fuse for the 42-volt system has blown or the battery cutoff switch (BCO) is off. 120V System Disabled: The Hybrid system temperature is too hot to function properly. 120V Ground Fault: A circuit imbalance between the hot and the neutral wires occurred while operating in either mode. 120 V Overload: Current flow in the circuit exceeded 20 amps. 120 V Ready: This message will be displayed and the light in the APO button will flash when the system is ready and waiting for operation in continuous mode. The light will flash for 30 seconds or until the key is placed in the lock position. 120 V System Fault: Some form of system fault has occurred. Battery Not Charging: If the Hybrid system fails to charge the 42-volt batteries or the 12-volt battery, the engine auto stop/start feature will be disabled and this message will be displayed. Engine Auto Start Mode: If the vehicle is in park, this message lets the driver know the engine could start at any time. This message will clear once the engine starts, if the vehicle is taken out of park, or if the ignition is moved to the lock position. Engine Coolant Hot: Engine is overheating. Fuel Level Low: Indicates the fuel level is low while the vehicle is operating in continuous mode. In addition to the DIC message, the BCM will command the horn to sound for 5 seconds every minute for 5 minutes. If the vehicle continues operating with a low fuel level, the engine will shut off after the 5 minutes of warning. Hood Ajar: The hood isn t fully closed. Oil Pressure Low: The engine will be shut off if this message displays while the vehicle is operating in continuous mode. Security: Indicates a security system violation has occurred. If the APO is being used, it ll be disabled. Service 42V Batteries: Indicates the batteries need service or replacement. Service Brake System: This message may be displayed if a problem with the steering system has occurred. In addition a chime may sound and the message may alternate with the message: Service Steering System. Well, that s about all for this part of the series. Next time we ll look at the service procedures for these systems. And in the meantime, don t forget: there s fire in those wires! 8 GEARS November/December 2006