GM Service Manual Online
For 1990-2009 cars only

Diagnostic Aids

Important: Perform the following in order to avoid misdiagnosis.

    • Inspect for proper operation of brake lamps.
    • Inspect throttle linkage for mechanical binding which could cause the system to malfunction.
    • When testing vehicles equipped with steering wheel controls, the steering wheel must be rotated to each stop position while testing the cruise control switch signal circuits. This will ensure the integrity of the SIR coil.
    • Inspect for stored Diagnostic Trouble Codes (DTCs) in the PCM.
    • Electromagnetic interference (EMI) on the speed sensor signal circuit may cause erratic cruise control operation.

Conditions for Enabling Cruise Control

    • When vehicle speed is more than 40 km/h (25 mph)
    • When PARK, REVERSE, NEUTRAL, or 1st gear is not indicated
    • When an over/undercharged battery condition does not exist
    • With normal engine RPM
    • Without high engine RPM (fuel cut-off)

Step

Action

Value(s)

Yes

No

Schematic Reference: Cruise Control Schematics

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

Does the test lamp illuminate?

--

Go to Step 3

Go to Step 35

3

Connect the test lamp between the ignition 3 voltage circuit and the ground circuit of the cruise control module.

Does the test lamp illuminate?

--

Go to Step 4

Go to Step 36

4

Turn the cruise control On/Off switch OFF.

Does the test lamp illuminate on any of the circuits?

--

Go to Step 15

Go to Step 5

5

  1. Turn ON the ignition, with the engine OFF.
  2. Turn ON the cruise control.
  3. Probe the cruise control on signal circuit with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

--

Go to Step 6

Go to Step 16

6

  1. Probe the cruise control set/coast signal circuit with a test lamp that is connected to a good ground.
  2. Press and hold the SET/COAST switch.

Does the test lamp illuminate?

--

Go to Step 7

Go to Step 18

7

  1. Probe the cruise control resume/accelerate signal circuit with a test lamp that is connected to a good ground.
  2. Press and hold the RESUME/ACCEL switch.

Does the test lamp illuminate?

--

Go to Step 8

Go to Step 19

8

Probe the TCC/Brake switch signal circuit with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

--

Go to Step 9

Go to Step 20

9

Probe the stop lamp switch signal circuit with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

--

Go to Step 22

Go to Step 10

10

Press the brake pedal while monitoring the test lamp.

Does the test lamp illuminate?

--

Go to Step 11

Go to Step 23

11

Probe the cruise control inhibit signal circuit with a test lamp that is connected to B+.

Does the test lamp illuminate?

--

Go to Step 12

Go to Step 25

12

Use a scan tool in order to command the cruise inhibit/enable OFF.

Does the test lamp illuminate?

--

Go to Step 24

Go to Step 13

13

Probe the cruise control engaged signal circuit with a DMM that is connected to a good ground.

Does the voltage measure near the specified value?

B+

Go to Step 14

Go to Step 26

14

Check the speedometer for proper operation.

Does the speedometer operate properly?

--

Go to Step 27

Go to Speedometer and/or Odometer Inaccurate or Inoperative in Instrument Panel, Gages and Console

15

Test the circuit that illuminated the test lamp 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 42

Go to Step 33

16

Test the cruise control on signal circuit for an open or a high resistance and the cruise control set/coast, resume/accel signal circuits 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 42

Go to Step 17

17

Test the ignition positive voltage circuit of the cruise control switch for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 42

Go to Step 33

18

Test the cruise control set/coast 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 42

Go to Step 33

19

Test the cruise control resume/accelerate 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 42

Go to Step 33

20

Test the TCC/Brake 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 42

Go to Step 28

21

Test the TCC/Brake 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 42

Go to Step 28

22

Test the stop lamp 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 42

Go to Step 29

23

Test the stop lamp 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 42

Go to Step 29

24

Test the cruise control inhibit 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 42

Go to Step 32

25

Test the cruise control inhibit signal circuit for an open, a high resistance, 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 42

Go to Step 32

26

Test the cruise control engaged signal circuit for an open, a high resistance, 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 42

Go to Step 32

27

Test the speed sensor circuit for an open or a high resistance between the cruise control module and the powertrain control module (PCM). Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 42

Go to Step 32

28

Inspect the TCC/Brake switch for proper adjustment. Refer to Stop Lamp Switch Adjustment in Lighting Systems.

Did you find and correct the condition?

--

Go to Step 42

Go to Step 30

29

Inspect the stop lamp switch for proper adjustment. Refer to Stop Lamp Switch Adjustment in Lighting Systems.

Did you find and correct the condition?

--

Go to Step 42

Go to Step 31

30

Inspect for poor connections at the harness connector of the TCC/Brake 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 42

Go to Step 37

31

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 42

Go to Step 38

32

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 42

Go to Step 39

33

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 42

Go to Step 40

34

Inspect for poor connections at the harness connector of the cruise control 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 42

Go to Step 41

35

Repair the ignition positive voltage circuit of the cruise control module. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 42

--

36

Repair the ground circuit of the cruise control module. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 42

--

37

Replace the TCC/Brake switch. Refer to Stop Lamp Switch Replacement in Lighting Systems.

Did you complete the replacement?

--

Go to Step 42

--

38

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

Did you complete the replacement?

--

Go to Step 42

--

39

Important: The PCM must be reprogrammed after replacement.

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 42

--

40

Replace the cruise control switch. Refer to Steering Wheel Control Switch Assembly Replacement in Steering Wheel and Column.

Did you complete the replacement?

--

Go to Step 42

--

41

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

Did you complete the replacement?

--

Go to Step 42

--

42

Operate the vehicle within the conditions for cruise control operation.

Does the cruise control system operate correctly?

--

System OK

Go to Step 2