Cruise Control Diagnosis

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Maximillian Townsend
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1 1999 Pontiac Firebird Cruise Control Diagnosis Circuit Description The Cruise Control system is a speed control system that maintains a desired vehicle speed under normal driving conditions. The cruise control system has the capability of the following: Cruise Coast Resume speed Accelerate Raise (Tap-up) the vehicle speed by 1.6 km/h (1 mph) Lower (Tap-down) the vehicle speed by 1.6 km/h (1 mph) The PCM controls the cruise system. When the cruise control switch is in the ON position and you push the cruise SET/COAST switch, the PCM maintains the current vehicle speed. If the engine load varies, the PCM commands the

2 throttle blade to the appropriate position in order to maintain the desired vehicle speed. The cruise control system consists of the following components: Powertrain Control Module (PCM) Throttle Actuator Control (TAC) Module Throttle body/tac assembly Cruise Control Actuator Lever Conditions for Enabling the Cruise System The Cruise switch is in the ON position. The ignition voltage is between 9 and 16 volts. Ignition voltage is present to the cruise actuator lever. The vehicle speed is greater than 39 km/h (24 mph). The engine speed is between 550 and 5900 RPM. The clutch or brake pedal is not depressed. The transmission is in a forward gear other than first. The vehicle is not in a traction control event. The engine is not in Engine Coolant Over Temperature-Fuel Disabled mode. The engine has been running for more than 5 seconds. Conditions for Disabling the Cruise System The Cruise switch is turned to the OFF position. Ignition voltage is interrupted to the cruise actuator lever. The vehicle speed is less than 39 km/h (24 mph). The clutch or brake pedal is depressed. The engine is in Engine Coolant Over Temperature-Fuel Disabled mode. The transmission is placed into neutral. A problem with the clutch or brake pedal switches or circuits that the PCM module interprets as the pedal is applied. Diagnostic Aids Use the scan tool in order to monitor the Cruise Disengage History. This parameter lists the last 8 cruise disengage events. Refer to Cruise Disengage History table for a description of each condition. The cruise control system disables for the current ignition cycle if an intermittent condition exists and DTC P0567 or DTC P0568 sets. Cruise Control Disengage Definitions Scan Tool Display Definition ALDL The PCM detects the scan tool has sent a inhibit message via serial data. Bad Memory Brake Pedal Initialize Cancel Clutch Switch The cruise system has detected a RAM corruption. The PCM detects one of the brake switches active (TCC Brake Switch/Cruise Control Brake Switch or Stop Lamp Switch). The PCM does not detect the brake switch active during an ignition cycle. (Auto Trans only) The PCM detects the cruise cancel switch has been depressed. The PCM detects the clutch has been depressed.

3 Coast Disengage Coast Speed Low Eng Run Time Eng Speed The PCM senses the vehicle speed is greater than 8 km/h (5 mph) below the set speed or the coast button is depressed for longer than 3 seconds. The Set/Coast switch is pushed and held until vehicle speed drops below 32 km/h (20 mph). Vehicle speed below 32 km/h (20 mph) will disable the cruise system. The PCM has detected the engine has not been running for longer than 5 seconds. The PCM has detected the engine speed is not between 550 and 5900 RPM. TAC Inhibit The PCM has detected that an Electronic Throttle Control fault is active. The PCM has detected DTCs P0500, P0502, P0503, P0560, P0567, P0568, P0571, P0704, P0719, DTC Set P0724, P0751, P0753, P0756, P0758, P0785 or P1574 are present. Accel Rate The vehicle acceleration is greater than the expected acceleration rate which is calculated by the PCM. Decel Rate The vehicle deceleration is greater than the expected deceleration rate which is calculated by the PCM. High Speed The PCM detects that the vehicle speed is greater than 225 km/h (140 mph). Illegal CC Mode The PCM will not allow cruise with the current position of the cruise switches. INJ Disable The PCM detect the Fuel Disable Mode is active. Low Speed The PCM detects that the vehicle speed is less than 39 km/h (24 mph) when cruise enable is attempted. Man Neutral CC MPH Limited Cruise Off Over Set Speed S/C On- Speed High Simul SC/RA Sw Traction Loss Under Set Speed First Gear Pedal Greater CC Ignition Volts Trans Wheel Speed Low The PCM has detected the transmission is in neutral. The PCM has detected that high speed fuel cutoff has been reached. The PCM does not detect that the cruise enable switch is active. The TAC module detects that the vehicle speed is greater than the cruise memory speed by more than a predetermined amount or, the vehicle speed is greater than a predetermined value during a transient maneuver, such as, Resume, Accel, Tap-up or Tap-downs etc. This parameter is displayed when the Set/Coast switch is applied (tap down vehicle speed) and the vehicle speed is greater than the cruise memory speed by more than a predetermined value. For example, if the cruise control system is set to maintain a vehicle speed of 48 km/h (30 mph) then the vehicle is accelerated to 80 km/h (50 mph) and you depress the Set/Coast again, the S/C On-Speed High message appears in the Cruise Control Disengage History. The PCM detects the Set/Coast and Resume/Accel switches are active at the same time. The PCM module detects the vehicle is in a Traction Control event. The PCM detects that the vehicle speed is less than the cruise memory speed by more than a predetermined amount or, the vehicle speed is less than a predetermined value during a transient maneuver, such as, Resume, Accel, Tap-up or Tap-downs etc. When the PCM detects the vehicle is in first gear. The PCM senses the accelerator pedal is at a greater value than the commanded cruise position for more than 1 minute. The PCM detect voltage out of the range of 9 to 16 volts. The PCM detect the transmission is not in forward gear higher than 1st gear (auto trans) or the clutch is depressed (manual trans). The PCM has detected the driven (rear) wheels are at a greater speed than the front wheels. Wheel The PCM has detected the driven (rear) wheels are at a lower speed than the front wheels.

4 Speed High MPH Governor The PCM detects the vehicle has reached 190 km/h (118 mph). RPM Governor The PCM detects the engine has reached 5900 RPM. Cruise Control System Check Step Action Value (s) Yes No 1 2 Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? Are DTCs P0567, P0568, P0571, P0601, P0602, P0606, P0704, P1574 or any Electronic Throttle Control system faults set? Go to Powertrain On Board Go to Step 2 Diagnostic (OBD) System Check Go to Applicable DTC Table Go to Step 3 3 Is the CRUISE CONTROL IGN fuse open? Go to Step 9 Go to Step Turn ON the ignition, with the engine 2. Turn ON the cruise switch. 3. With a scan tool, monitor the TCC, Cruise Release and TAC Brake Switch parameters. 4. Apply the brake. Does the scan tool display brake switch parameters RELEASED and switch to APPLIED when the brake pedal was pressed? Important This step is for manual transmission vehicles only. If the vehicle has an automatic transmission, refer to step 6. Go to Step 5 Go to DTC P0571 (Cruise Brake Switch) or DTC P0719, P0724 (TCC Brake Switch) or DTC P1574 (TAC Brake Switch) 5 6 With a scan tool, monitor the Clutch Anticipate switch parameter while depressing the clutch pedal. Does the scan tool display Applied as the clutch is Depressed? 1. Turn ON the Cruise switch. 2. With a scan tool, monitor the Cruise Switch parameter. Go to Step 6 Go to DTC P Does the scan tool display Cruise Switch as ON? 1. With a scan tool, monitor the Cruise Set/Coast parameter. 2. Push the Cruise Set/Coast switch in. Does the scan tool display Cruise Set/Coast ON when the switch was pushed in? Go to Step 7 Go to Step 15 Go to Step 8 Go to Step With a scan tool, monitor the Cruise Resume/Accel parameter.

5 2. Push the Cruise Resume/Accel switch in. 8 Does the scan tool display Cruise Resume/Accel as ON when the switch was pushed in? System OK Go to Step Probe the cruise ignition feed circuit, fuse side of the circuit, using a J B Test Lamp that is connected to B+. Does the test lamp illuminate? Go to Step 31 Go to Step Probe the cruise ON/OFF signal circuit (TAC Module side of the circuit) using a J B Test Lamp that is connected to B+. Does the test lamp illuminate? Go to Step 11 Go to Step Test lamp still connected to the cruise ON/OFF signal circuit (TAC Module side of the circuit), 2. Disconnect the TAC module. Did the test lamp go OFF when the TAC module was disconnected? Go to Step 30 Go to Step Replace the fuse for the cruise control circuit. 2. Push the Cruise Set/Coast switch ON. Did the fuse open when the switch was pushed in? Go to Step 14 Go to Step 13 Push the Cruise Resume/Accel switch ON. 13 Did the fuse open when the switch was pushed in? Go to Step 14 Go to Diagnostic Aids 14 Repair the grounded circuit between the TAC module and the Cruise Control Lever. Refer to Wiring Repairs. System OK Turn ON the ignition, with the engine 4. Probe the cruise ignition feed circuit, fuse side of the circuit, using a test lamp that is connected to a good ground. Does the test lamp illuminate? Go to Step 16 Go to Step Probe the cruise ON/OFF signal circuit (TAC module side of the circuit), using a fused jumper wire that is connected to B+. 2. With a scan tool, monitor the Cruise

6 Switch parameter. 16 Does the scan tool display Cruise Switch as ON? Go to Step 28 Go to Step Disconnect the TAC module. 2. Check the continuity of the Cruise ON/OFF signal circuit using a DMM. Is continuity indicated? Go to Step 27 Go to Step Repair the Cruise ON/OFF signal circuit for an open. Refer to Wiring Repairs. System OK Turn ON the ignition, with the engine 4. Probe the Cruise Set/Coast signal circuit (TAC Module side) using a fused jumper wire that is connected to B+. 5. With a scan tool, monitor the Cruise Set/Coast parameter. Does the scan tool display the Cruise Set/Coast parameter as ON when the voltage was applied? Go to Step 28 Go to Step Disconnect the TAC module. 2. Check the continuity of the Cruise Set/Coast signal circuit using a DMM. Is continuity indicated? Go to Step 27 Go to Step Repair the Cruise Set/Coast signal circuit for an open. Refer to Wiring Repairs. System OK Turn ON the ignition, with the engine 4. Probe the Cruise Resume/Accel signal circuit (TAC Module side) using a fused jumper wire that is connected to B+. 5. With a scan tool, monitor the Cruise Resume/Accel parameter. Does the scan tool display the Cruise Resume/Accel parameter as ON when the voltage was applied? Go to Step 28 Go to Step Disconnect the TAC module. 2. Check continuity of the Cruise Resume/Accel signal circuit using a DMM. Is continuity indicated? Go to Step 27 Go to Step 24

7 Repair the Cruise Resume/Accel signal circuit for an open. Refer to Wiring Repairs. Repair the open circuit between the Cruise Control Lever and the fuse block. Refer to Wiring Repairs. 1. Repair the grounded circuit between the Cruise Control Lever and the TAC module. Refer to Wiring Repairs. 2. Replace the fuse. 1. Inspect the circuit for a short to ground. 2. If a problem is found repair as necessary. Refer to Wiring Repairs. Did you find and correct the condition? Replace the Cruise Control Lever (multifunction lever). 1. Check for poor connections at the TAC module. 2. If a problem is found repair as necessary. Refer to Testing for Intermittent and Poor Connections. Did you find and correct the condition? Replace the TAC module. Refer to Accelerator Controls Pedal Replacement. 1. Repair the grounded circuit between the Cruise Control Lever and the fuse. Refer to Wiring Repairs. 2. Replace the fuse. System OK System OK System OK System OK Go to Step 29 System OK System OK Go to Step 30 System OK System OK

SCHEMATIC AND ROUTING DIAGRAMS

2004 ACCESSORIES & EQUIPMENT Cruise Control - Corvette SCHEMATIC AND ROUTING DIAGRAMS CRUISE CONTROL SCHEMATICS Fig. 1: Cruise Control Switch, Throttle Actuator Control Motor And Cruise Control Release