For 1990-2009 cars

### Diagnostic Aids

Important: Perform the following in order to avoid misdiagnosis.

• | Inspect for proper operation of brake lamps and clutch switch, if equipped.

• | EMI on the speed sensor signal circuit may cause erratic cruise control operation.

### Conditions for Enabling Cruise Control

The vehicle speed is greater than 40 km/h (25 mph).

### Test Description

The numbers below refer to step numbers on the diagnostic table.

1. The TAC module and PCM receive brake pedal position from the stop lamp interface module, regardless of how many stop lamp switches the vehicle is equipped with.

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: Cruise Control Schematics
1 | Did you perform A Diagnostic System Check - Cruise Control? | Go to Step 2 | Go to Diagnostic System Check - Cruise Control
2 |

1. Connect a scan tool.
2. Observe the Cruise On switch parameter in the throttle actuator control (TAC) module data list.
3. Turn ON the cruise control switch.

Did the scan tool parameter change state?

Go to Step 3

Go to Step 17

3 |

1. Observe the cruise control Set/Coast parameter in the TAC module data list.
2. Press the cruise control Set button.

Did the cruise control Set/Coast parameter change state?

Go to Step 4

Go to Step 20

4 |

1. Observe the cruise control Resume/Accelerate parameter in the TAC module data list.
2. Press the Resume/Accelerate switch.

Did the cruise control Resume Accelerate parameter change state?

Go to Step 5

Go to Step 21

5 |

1. Observe the stop lamp pedal switch parameter in the TAC module data list.
2. Press the brake pedal.

Did the stop lamp pedal switch parameter change state?

Go to Step 11

Go to Step 6

6 |

1. Turn OFF the ignition.
2. Disconnect the stop lamp interface module.
3. Turn ON the ignition, with the engine OFF.
4. Probe the stop lamp interface module harness connector ignition positive voltage circuit with a test lamp connected to a good ground.

Does the test lamp illuminate?

Go to Step 7

Go to Step 30

7 | Probe the stop lamp interface module harness connector ignition positive voltage circuit with a test lamp connected to the ground circuit of the stop lamp interface module. Does the test lamp illuminate? | Go to Step 8 | Go to Step 31
8 | Probe the stop lamp interface module harness connector stop lamp signal circuit, from the stop lamp switch, with a test lamp connected to a good ground. Does the test lamp illuminate? | Go to Step 22 | Go to Step 9
9 | Press the brake pedal. Does the test lamp illuminate? | Go to Step 24 | Go to Step 10
10 |

1. Turn OFF the ignition.
2. Disconnect the stop lamp switch harness connector.
3. Turn ON the ignition, with the engine OFF.
4. Probe the stop lamp switch harness connector ignition positive voltage circuit with a test lamp connected to a good ground.

Go to Step 23

Go to Step 32

11 |

1. Observe the TCC/Brake pedal switch parameter in the PCM data list.
2. Press the brake pedal.

Did the TCC/Brake pedal switch parameter change state?

Go to Step 15

Go to Step 12

12 |

1. Turn OFF the ignition.
2. Disconnect the stop lamp interface module harness connector.
3. Probe the brake switch signal circuit with a test lamp connected to battery voltage.

Does the test lamp illuminate?

Go to Step 13

Go to Step 14

13 |

1. Press the brake pedal.
2. Observe the test lamp.

Does the test lamp illuminate?

Go to Step 27

Go to Step 25

14 |

1. Turn OFF the ignition.
2. Disconnect the stop lamp switch harness connector.
3. Probe the stop lamp switch harness connector ground circuit with a test lamp connected to battery positive.

Does the test lamp illuminate?

Go to Step 26

Go to Step 33

15 | Is the vehicle equipped with a manual transmission? | Go to Step 16 | Go to Step 39
16 |

1. Observe the clutch pedal position (CPP) switch parameter in the PCM data list.
2. Press the clutch pedal.

Did the CPP switch parameter change state?

Go to Step 39

Go to Step 18

17 |

1. Turn OFF the ignition.
2. Disconnect the multifunction turn signal lever.
3. Turn ON the ignition, with the engine OFF.
4. Probe the cruise control switch ignition positive voltage circuit with a test lamp connected to a good ground.

Does the test lamp illuminate?

Go to Step 19

Go to Step 29

18 |

1. Turn OFF the ignition.
2. Disconnect the clutch pedal position (CPP) switch.
3. Turn ON the ignition, with the engine OFF.
4. Probe the CPP switch ignition positive voltage circuit with a test lamp connected to a good ground.

Does the test lamp illuminate?

Go to Step 28

Go to Step 34

19 | Test the cruise control ON switch signal circuit for a open, high resistance, short to ground or short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 45 | Go to Step 37
20 | Important: On vehicles equipped with upfitter equipment, the upfitter wiring harness must be tested. Test the cruise control Set/Coast signal circuit for a open, high resistance, short to ground or short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 45

Go to Step 37

21 | Important: On vehicles equipped with upfitter equipment, the upfitter wiring harness must be tested. Test the cruise control Resume/Accelerate signal circuit for a open, high resistance, short to ground or short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 45

Go to Step 37

22 | Test the stop lamp switch signal circuit between the stop lamp switch and the interface module for a short to battery positive. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 45 | Go to Step 35
23 | Test the stop lamp switch signal circuit between the stop lamp switch and the interface module for a open or a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 45 | Go to Step 35
24 | Test the stop lamp switch signal circuit between the TAC module and stop lamp interface module for a open, high resistance, short to ground or a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 45 | Go to Step 38
25 | Test the TCC/Brake switch signal circuit between the PCM and stop lamp interface module for a open, high resistance, short to ground or short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 45 | Go to Step 38
26 | Test the brake switch signal circuit for a open, high resistance or short to battery positive. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 45 | Go to Step 35
27 | Test the brake switch signal circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 45 | Go to Step 35
28 | Test the CPP switch signal circuit for a open, high resistance, short to ground or short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 45 | Go to Step 36
29 | Important: On vehicles equipped with upfitter equipment, the ignition positive voltage circuit to the PTO switch must be tested. Repair the open, high resistance or short to ground in the multifunction turn signal lever ignition positive voltage circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 45

--

30 | Repair the open, high resistance or short to ground in the stop lamp interface module ignition positive voltage circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 45 | --
31 | Repair the open, high resistance or short to battery positive in the stop lamp interface module ground circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 45 | --
32 | Important: On vehicles equipped with upfitter equipment, all stop lamp switch ignition positive voltage circuits must be tested. Repair the open, high resistance or short to ground in the stop lamp switch battery positive voltage circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 45

--

33 | Repair the open, high resistance or short to voltage in the stop lamp switch ground circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 45 | --
34 | Repair the open, high resistance or short to ground in the CPP switch battery positive voltage circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 45 | --
35 | Inspect for poor connections at the harness connector of the stop lamp switch. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 45 | Go to Step 40
36 | Inspect for poor connections at the harness connector of the CPP switch. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 45 | Go to Step 41
37 | Inspect for poor connections at the harness connector of the multifunction turn signal lever. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 45 | Go to Step 42
38 | Inspect for poor connections at the harness connector of the stop lamp interface module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 45 | Go to Step 43
39 | Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 45 | Go to Step 44
40 | Replace the stop lamp switch. Refer to Stop Lamp Switch Replacement in Hydraulic Brakes. Did you complete the replacement? | Go to Step 45 | --
41 | Replace the CPP switch. Refer to Clutch Pedal Position Switch Replacement in Clutch. Did you complete the replacement? | Go to Step 45 | --
42 | Replace the multifunction turn signal lever. Refer to Turn Signal Multifunction Switch Replacement in Steering Wheel and Column. Did you complete the replacement? | Go to Step 45 | --
43 | Replace the stop lamp switch interface module. Did you complete the replacement? | Go to Step 45 | --
44 | Important: The PCM must be reprogrammed after replacement. Refer to Powertrain Control Module Programming in Engine Controls - 8.1L. Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls - 8.1L. Did you complete the replacement? | Go to Step 45 | --
45 | Operate the vehicle with in the conditions for cruise control operation. Does the cruise control system operate properly? | System OK | Go to Step 2