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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2005 🢒 TopKick C-Series (Conventional) C4/C5 🢒 Accessories 🢒 Cruise Control 🢒 Cruise Control Inoperative/Malfunctioning

Cruise Control Inoperative/Malfunctioning 6.6L

Diagnostic Aids

To avoid a misdiagnosis, inspect for the following:

    • Proper operation of the stop lamps--Refer to Exterior Lighting Systems Description and Operation in Lighting Systems.
    • Proper operation of the clutch system, if equipped with a manual transmission--Refer to Clutch System Description and Operation in Clutch.
    • The throttle linkage is not binding.

Electromagnetic interference (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).
    • The vehicle is not in PARK, REVERSE, NEUTRAL, or 1st gear.
    • The system voltage is between 12-16 volts.

Step

Action

Yes

No

Schematic Reference: Cruise Control Schematics

Connector End View Reference: Engine Control Module Connector End Views in Engine Controls - 6.6L (LLY)

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2
  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Turn the cruise control On/Off switch OFF.
  4. With the scan tool, observe the Cruise On/Off Switch parameter in the powertrain control module (PCM) Engine Data 1 data list.

Does the Cruise On/Off Switch parameter display Off?

Go to Step 3

Go to Step 6

3
  1. Turn the cruise control On/Off switch ON.
  2. With the scan tool, observe the Cruise On/Off Switch parameter.

Does the Cruise On/Off Switch parameter display On?

Go to Step 4

Go to Step 10

4
  1. With the scan tool, observe the Cruise Set/Coast Switch parameter in the PCM Engine Data 1 data list.
  2. Turn the cruise control On/Off switch ON.
  3. Press and hold the cruise control Set/Coast switch.

Does the Cruise Set/Coast Switch parameter display On?

Go to Step 5

Go to Step 7

5
  1. With the scan tool, observe the Cruise Resume/Accel. Switch parameter in the PCM data list.
  2. Press and hold the Resume/Accel switch.

Does the Cruise Resume/Accel. Switch parameter display On?

Go to Step 9

Go to Step 8

6
  1. Turn OFF the ignition.
  2. Disconnect the cruise control switch.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a test lamp between the cruise control on switch signal circuit and a good ground.

Does the test lamp illuminate?

Go to Step 11

Go to Step 20

7
  1. Turn OFF the ignition.
  2. Disconnect the cruise control switch.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a 3-ampere fused jumper between the cruise control set/coast switch signal circuit and the ignition 3 voltage circuit.
  5. With the scan tool, observe the Cruise Set/Coast Switch parameter.

Does the Cruise Set/Coast Switch parameter display On?

Go to Step 20

Go to Step 15

8
  1. Turn OFF the ignition.
  2. Disconnect the cruise control switch.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a 3-ampere fused jumper between the cruise control resume/accel switch signal circuit and the ignition 3 voltage circuit.
  5. With the scan tool, observe the Cruise Resume/Accel. Switch parameter.

Does the Cruise Resume/Accel. Switch parameter display On?

Go to Step 20

Go to Step 16

9
  1. With the scan tool, observe the TCC Cruise Brake Pedal parameter in the PCM Engine Data 1 data list.
  2. Depress the brake pedal.

Does the TCC Cruise Brake Pedal parameter display Applied?

Go to Diagnostic Aids

Go to Step 17

10
  1. Turn OFF the ignition.
  2. Disconnect the cruise control switch.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a test lamp between the ignition 3 voltage circuit and a good ground.

Does the test lamp illuminate?

Go to Step 12

Go to Step 18

11

Test the cruise control on switch signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 25

Go to Step 21

12

Test the cruise control on switch signal circuit for the following:

    • An open
    • A high resistance
    • A short to ground

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 25

Go to Step 13

13

Test the cruise control resume/accel 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 25

Go to Step 14

14

Test the cruise control set/coast 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 25

Go to Step 20

15

Test the cruise control set/coast switch signal circuit for an 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 25

Go to Step 21

16

Test the cruise control resume/accel switch signal circuit for an 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 25

Go to Step 21

17

Test the torque converter clutch (TCC)/Brake switch signal circuit for the following:

    • An open
    • A high resistance
    • A short to ground

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 25

Go to Step 19

18

Repair the following in the ignition 3 voltage circuit:

    • An open
    • A high resistance
    • A short to ground

Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 25

--

19

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 25

Go to Step 22

20

Inspect for poor connections at the harness connector of the cruise control 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 25

Go to Step 23

21

Inspect for poor connections at the harness connector of the engine control module (ECM). 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 25

Go to Step 24

22

Replace the stop lamp switch. Refer to Stop Lamp Switch Replacement in Lighting Systems.

Did you complete the replacement?

Go to Step 25

--

23

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 25

--

24

Replace the ECM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 25

--

25

Operate the vehicle within the conditions for cruise control operation.

Does the cruise control system operate properly?

System OK

Go to Step 2

Cruise Control Inoperative/Malfunctioning 7.8L

Diagnostic Aids

To avoid a misdiagnosis, inspect for the following conditions:

    • Proper operation of the stop lamps--Refer to Exterior Lighting Systems Description and Operation in Lighting Systems.
    • Proper operation of the clutch system, if equipped with a manual transmission--Refer to Clutch System Description and Operation in Clutch.
    • The throttle linkage is not binding.

Electromagnetic interference (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).
    • The vehicle is not in PARK, REVERSE, NEUTRAL, or 1st gear.
    • The system voltage is between 12-16 volts.

Step

Action

Yes

No

Schematic Reference: Cruise Control Schematics

Connector End View Reference: Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2
  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Turn the cruise control On/Off switch OFF.
  4. With the scan tool, observe the Cruise On/Off Switch parameter in the powertrain control module (PCM) Engine Data 1 data list.

Does the Cruise On/Off Switch parameter display Off?

Go to Step 3

Go to Step 6

3
  1. Turn the cruise control On/Off switch ON.
  2. With the scan tool, observe the Cruise On/Off Switch parameter.

Does the Cruise On/Off Switch parameter display On?

Go to Step 4

Go to Step 10

4
  1. With the scan tool, observe the Cruise Set/Coast Switch parameter in the PCM Engine Data 1 data list.
  2. Turn the cruise control On/Off switch ON.
  3. Press and hold the cruise control Set/Coast switch.

Does the Cruise Set/Coast Switch parameter display On?

Go to Step 5

Go to Step 7

5
  1. With the scan tool, observe the Cruise Resume/Accel. Switch parameter in the PCM data list.
  2. Press and hold the Resume/Accel switch.

Does the Cruise Resume/Accel. Switch parameter display On?

Go to Step 9

Go to Step 8

6
  1. Turn OFF the ignition.
  2. Disconnect the cruise control switch.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a test lamp between the cruise control on switch signal circuit and a good ground.

Does the test lamp illuminate?

Go to Step 11

Go to Step 20

7
  1. Turn OFF the ignition.
  2. Disconnect the cruise control switch.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a 3-amp fused jumper between the cruise control set/coast switch signal circuit and the ignition 1 voltage circuit.
  5. With the scan tool, observe the Cruise Set/Coast Switch parameter.

Does the Cruise Set/Coast Switch parameter display On?

Go to Step 20

Go to Step 15

8
  1. Turn OFF the ignition.
  2. Disconnect the cruise control switch.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a 3-amp fused jumper between the cruise control resume/accel switch signal circuit and the ignition 3 voltage circuit.
  5. With the scan tool, observe the Cruise Resume/Accel. Switch parameter.

Does the Cruise Resume/Accel. Switch parameter display On?

Go to Step 20

Go to Step 16

9
  1. With the scan tool, observe the Stoplamp Pedal Switch parameter in the PCM Engine Data 1 data list.
  2. Depress the brake pedal.

Does the Stoplamp Pedal Switch parameter display Applied?

Go to Diagnostic Aids

Go to Step 17

10
  1. Turn OFF the ignition.
  2. Disconnect the cruise control switch.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a test lamp between the ignition 1 voltage circuit and a good ground.

Does the test lamp illuminate?

Go to Step 12

Go to Step 18

11

Test the cruise control on switch signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 25

Go to Step 21

12

Test the cruise control on switch signal circuit for the following:

    • An open
    • A high resistance
    • A short to ground

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 25

Go to Step 13

13

Test the cruise control resume/accel 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 25

Go to Step 14

14

Test the cruise control set/coast 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 25

Go to Step 20

15

Test the cruise control set/coast switch signal circuit for an 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 25

Go to Step 21

16

Test the cruise control resume/accel switch signal circuit for an 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 25

Go to Step 21

17

Test the stop lamp switch signal circuit for the following:

    • An open
    • A high resistance
    • A short to ground

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 25

Go to Step 19

18

Repair the following in the ignition 1 voltage circuit:

    • An open
    • A high resistance
    • A short to ground

Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 25

--

19

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 25

Go to Step 22

20

Inspect for poor connections at the harness connector of the cruise control 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 25

Go to Step 23

21

Inspect for poor connections at the harness connector of the engine control module (ECM). 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 25

Go to Step 24

22

Replace the stop lamp switch. Refer to Stop Lamp Switch Replacement in Lighting Systems.

Did you complete the replacement?

Go to Step 25

--

23

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 25

--

24

Replace the ECM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 25

--

25

Operate the vehicle within the conditions for cruise control operation.

Does the cruise control system operate properly?

System OK

Go to Step 2

Cruise Control Inoperative/Malfunctioning 8.1L

Diagnostic Aids

Perform the following in order to avoid a misdiagnosis:

    • Inspect for proper operation of the stop lamps. Refer to Exterior Lighting Systems Description and Operation in Lighting Systems.
    • Electromagnetic interference (EMI) on the vehicle speed sensor signal circuit may cause erratic cruise control operation.

For an intermittent condition, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Conditions for Enabling Cruise Control
    • The vehicle speed is greater than 40 km/h (25 mph).
    • The vehicle is not in PARK, REVERSE, NEUTRAL, or 1st gear.
    • The system voltage is within 12-16 volts.

Test Description

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

  1. This step tests the center high mounted stop lamp (CHMSL) supply voltage/stop lamp supply voltage circuit for an open or a high resistance between the stop lamp switch and the throttle actuator control (TAC) module.

    2.

  2. This step tests the cruise control set/coast switch signal circuit for an open or a high resistance.

    3.

  3. This step tests the cruise control resume/accel switch signal circuit for an open or a high resistance.

    4.

  4. This step tests the ignition 1 voltage circuit for an open, a short to ground, or a high resistance.

    5.

  5. DTCs will set in the powertrain control module (PCM) when you perform this table.

Step

Action

Yes

No

Schematic Reference : Cruise Control Schematics

Connector End View Reference: Powertrain Control Module Connector End Views in Engine Controls - 8.1L

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2
  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Turn the cruise control On/Off switch OFF.
  4. With the scan tool, observe the Cruise On/Off Switch parameter in the powertrain control module (PCM) Cruise Control Data data list.

Does the Cruise On/Off Switch parameter display Off?

Go to Step 4

Go to Step 3

3
  1. Turn OFF the ignition.
  2. Disconnect the cruise control switch.
  3. Turn ON the ignition, with the engine OFF.
  4. With the scan tool, observe the Cruise On/Off Switch parameter.

Does the Cruise On/Off Switch parameter display Off?

Go to Step 22

Go to Step 13

4
  1. Turn the cruise control On/Off switch ON.
  2. With the scan tool, observe the Cruise On/Off Switch parameter.

Does the Cruise On/Off Switch parameter display On?

Go to Step 5

Go to Step 11

5
  1. With the scan tool, observe the Cruise Set/Coast Switch parameter in the PCM Cruise Control Data data list.
  2. Turn the cruise control On/Off switch On.
  3. Press and hold the cruise control Set/Coast button.

Does the Cruise Set/Coast Switch parameter Display On?

Go to Step 6

Go to Step 9

6
  1. With the scan tool, observe the Cruise Resume/Accel. Switch parameter in the PCM Cruise Control Data data list.
  2. Press and hold the Resume/Accel switch.

Does the Cruise Resume/Accel. Switch parameter Display On?

Go to Step 7

Go to Step 10

7

Do the stop lamps operate properly?

Go to Step 8

Go to Stop Lamps Inoperative in Lighting Systems

8

  1. With the scan tool, observe the Stoplamp Pedal Switch parameter in the PCM Cruise Control Data data list.
  2. Depress and hold the brake pedal.

Does the Stoplamp Pedal Switch parameter Display Applied?

Go to Diagnostic Aids

Go to Step 21

9

  1. Turn OFF the ignition.
  2. Disconnect the cruise control switch.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a 3-ampere fused jumper between the cruise control set/coast switch signal circuit and the ignition 1 voltage circuit.
  5. With the scan tool, observe the Cruise Set/Coast Switch parameter.

Does the Cruise Set/Coast Switch parameter Display On?

Go to Step 22

Go to Step 19

10

  1. Turn OFF the ignition.
  2. Disconnect the cruise control switch.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a 3-ampere fused jumper between the cruise control resume/accel switch signal circuit and the ignition 1 voltage circuit.
  5. With the scan tool, observe the Cruise Resume/Accel. Switch parameter.

Does the Cruise Resume/Accel. Switch parameter Display On?

Go to Step 22

Go to Step 20

11

  1. Turn OFF the ignition.
  2. Disconnect the cruise control switch.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a test lamp between the ignition 1 voltage circuit and a good ground.

Does the test lamp illuminate?

Go to Step 12

Go to Step 15

12
  1. Connect a 3-ampere fused jumper between the ignition 1 voltage circuit and the cruise control on switch signal circuit.
  2. With the scan tool, observe the Cruise On/Off Switch parameter.

Does the Cruise On/Off Switch parameter display On?

Go to Step 22

Go to Step 18

13

Test the cruise control on switch signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 29

Go to Step 14

14
  1. Turn OFF the ignition.
  2. Disconnect C1 of the throttle actuator control (TAC) module.
  3. Turn ON the ignition, with the engine OFF.
  4. With the scan tool, observe the Cruise On/Off Switch parameter.

Does the Cruise On/Off Switch parameter display On?

Go to Step 24

Go to Step 23

15

Test the cruise control set/coast 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 29

Go to Step 16

16

Test the cruise control resume/accel 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 29

Go to Step 17

17

Test the cruise control on 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 29

Go to Step 25

18

Test the cruise control on switch signal circuit for an 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 29

Go to Step 23

19

Test the cruise control set/coast switch signal circuit for an 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 29

Go to Step 23

20

Test the cruise control resume/accel switch signal circuit for an 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 29

Go to Step 23

21

Test the center high mounted stop lamp (CHMSL) supply voltage/stop lamp supply voltage circuit for an open or a high resistance between the stop lamp switch and the TAC module. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 29

Go to Step 23

22

Inspect for poor connections at the harness connector of the cruise control 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 29

Go to Step 26

23

Inspect for poor connections at the harness connector of the TAC 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 29

Go to Step 27

24

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 29

Go to Step 28

25

Repair the following in the ignition 1 voltage circuit:

    • An open
    • A high resistance
    • A short to ground

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 29

--

26

Replace the cruise control switch. Refer to Turn Signal Multifunction Switch Replacement in Steering Wheel and Column.

Did you complete the replacement?

Go to Step 29

--

27

Replace the TAC module. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 29

--

28

Replace the PCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 29

--

29

  1. Use the scan tool in order to clear the PCM DTCs.
  2. Operate the vehicle within the conditions for cruise control operation.

Does the cruise control system operate properly?

System OK

Go to Step 2