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.
    • Inspect cruise control cable adjustment, should have minimum slack.
    • Inspect for stored Diagnostic Trouble Codes (DTCs) in the PCM.
    • 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 A Cruise Control System Check ?

--

Go to Step 2

Go to Cruise Control System Check

2

  1. Turn OFF the ignition.
  2. Disconnect the cruise control module.
  3. Turn the ignition to the RUN position.
  4. Probe the ignition positive voltage circuit of the cruise control module harness connector with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

--

Go to Step 3

Go to Step 36

3

Probe the ignition positive voltage circuit of the cruise control module harness connector with a test lamp that is connected to the ground circuit of the cruise control module harness connector.

Does the test lamp illuminate?

--

Go to Step 4

Go to Step 37

4

  1. Turn OFF the cruise control.
  2. Probe the cruise control module harness connector, on/off switch, set/coast switch, and the resume/accelerate switch signal circuits with a test lamp that is connected to a good ground.

Does the test lamp illuminate on any of the signal circuits?

--

Go to Step 16

Go to Step 5

5

  1. Turn ON the cruise control switch.
  2. Probe the cruise control module harness connector on/off switch 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 17

6

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

Does the test lamp illuminate?

--

Go to Step 7

Go to Step 19

7

  1. Probe the cruise control module harness connector resume/accelerate switch 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 20

8

Probe the cruise control module harness connector Abs/TCC, release 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 21

9

Press the brake pedal while monitoring the test lamp.

Does the test lamp illuminate?

--

Go to Step 22

Go to Step 10

10

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

Does the test lamp illuminate?

--

Go to Step 23

Go to Step 11

11

Press the brake pedal while monitoring the test lamp.

Does the test lamp illuminate?

--

Go to Step 12

Go to Step 24

12

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

Does the test lamp illuminate?

--

Go to Step 25

Go to Step 13

13

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

Does the test lamp illuminate?

--

Go to Step 14

Go to Step 26

14

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 15

Go to Step 27

15

Check the speedometer for proper operation.

Does the speedometer operate properly?

--

Go to Step 28

Go to Speedometer and/or Odometer Inoperative

16

Test the signal circuit that illuminated the test lamp for a short to voltage.

Did you find and correct the condition?

--

Go to Step 43

Go to Step 34

17

Test the cruise control on switch signal circuit for an open or a high resistance and the set/coast and resume/accel signal circuits for a short to ground.

Did you find and correct the condition?

--

Go to Step 43

Go to Step 18

18

Test the ignition positive voltage circuit for an open or high resistance between the IP junction block and the cruise control switch.

Did you find and correct the condition?

--

Go to Step 43

Go to Step 34

19

Test the cruise control set/coast signal circuit for an open or a high resistance.

Did you find and correct the condition?

--

Go to Step 43

Go to Step 34

20

Test the cruise control resume/accelerate signal circuit for an open or a high resistance.

Did you find and correct the condition?

--

Go to Step 43

Go to Step 34

21

Test the cruise control release switch signal circuit for an open or a high resistance.

Did you find and correct the condition?

--

Go to Step 43

Go to Step 29

22

Test the cruise control release switch signal circuit for a short to voltage.

Did you find and correct the condition?

--

Go to Step 43

Go to Step 29

23

Test the stoplamp switch signal circuit for a short to voltage.

Did you find and correct the condition?

--

Go to Step 43

Go to Step 30

24

Test the stoplamp switch signal circuit for an open or a high resistance.

Did you find and correct the condition?

--

Go to Step 43

Go to Step 30

25

Test the cruise inhibit signal circuit for a short to ground.

Did you find and correct the condition?

--

Go to Step 43

Go to Step 33

26

Test the cruise inhibit signal circuit for an open, a high resistance, or a short to voltage.

Did you find and correct the condition?

--

Go to Step 43

Go to Step 33

27

Test the cruise engaged signal circuit for an open, a high resistance, or a short to voltage.

Did you find and correct the condition?

--

Go to Step 43

Go to Step 33

28

Test the speed sensor circuit for an open or a high resistance between the PCM and cruise control module.

Did you find and correct the condition?

--

Go to Step 43

Go to Step 35

29

Inspect the cruise control release switch for proper adjustment. Refer to Brake Release Switch Adjustment .

Did you find and correct the condition?

--

Go to Step 43

Go to Step 31

30

Inspect the stoplamp switch for proper adjustment. Refer to Stop Lamp Switch Adjustment in Hydraulic Brakes.

Did you find and correct the condition?

--

Go to Step 43

Go to Step 32

31

Inspect for poor connections at the harness connector of the cruise control release switch.

Did you find and correct the condition?

--

Go to Step 43

Go to Step 38

32

Inspect for poor connections at the harness connector of the stoplamp switch.

Did you find and correct the condition?

--

Go to Step 43

Go to Step 39

33

Inspect for poor connections at the harness connector of the PCM.

Did you find and correct the condition?

--

Go to Step 43

Go to Step 40

34

Inspect for poor connections at the harness connector of the cruise control switch.

Did you find and correct the condition?

--

Go to Step 43

Go to Step 39

35

Inspect for poor connections at the harness connector of the cruise control module.

Did you find and correct the condition?

--

Go to Step 43

Go to Step 42

36

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 43

--

37

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

Did you complete the repair?

--

Go to Step 43

--

38

Replace the cruise control release switch. Refer to Brake Release Switch Replacement .

Did you complete the replacement?

--

Go to Step 43

--

39

Replace the stop lamp switch. Refer to Stop Lamp Switch Replacement in Hydraulic Brakes.

Did you complete the replacement?

--

Go to Step 43

--

40

Replace the PCM. Refer to Powertrain Control Module Replacement/Programming in Engine Controls.

Did you complete the replacement?

--

Go to Step 43

--

41

Replace the cruise control switch. Refer to Multifunction Turn Signal Lever Replacement - On Vehicle .

Did you complete the replacement?

--

Go to Step 43

--

42

Replace the cruise control module. Refer to Cruise Control Module Replacement .

Did you complete the replacement?

--

Go to Step 43

--

43

Operate the vehicle within the conditions for cruise control operation.

Does the cruise control system operate correctly?

--

System OK

Go to Step 2