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.
   • 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).

Step

Action

Value(s)

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. Turn OFF the ignition.
  2. Disconnect the cruise control module.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the ignition positive voltage circuit of the cruise control module with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

--

Go to Step 3

Go to Step 29

3

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

Does the test lamp illuminate?

--

Go to Step 4

Go to Step 30

4

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

Does the test lamp illuminate on any of the circuits?

--

Go to Step 14

Go to Step 5

5

  1. Turn ON the ignition, with the engine OFF.
  2. Turn ON the cruise control switch.
  3. Probe the cruise control on/off 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 15

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 17

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 18

8

Probe the TCC/Brake 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 19

9

Press the brake pedal while monitoring the test lamp.

Does the test lamp illuminate?

--

Go to Step 20

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 21

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 22

12

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 13

Go to Step 23

13

Check the speedometer for proper operation.

Does the speedometer operate properly?

--

Go to Step 24

Go to Symptoms - Instrument Panel, Gages and Console in Instrument Panel, Gages and Console

14

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 35

Go to Step 27

15

Test the cruise control on switch signal circuit for a open, high resistance or short to ground 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 35

Go to Step 16

16

Test the ignition positive voltage circuit for a open, high resistance or short to ground between the cruise control module and the cruise control switch. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 35

Go to Step 27

17

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 35

Go to Step 27

18

Test the cruise control resume/accelerate 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 35

Go to Step 27

19

Test the TCC/Brake 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 35

Go to Step 25

20

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 35

Go to Step 25

21

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 35

Go to Step 25

22

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 35

Go to Step 25

23

Test the cruise control engaged signal circuit for an open, a high resistance, or a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 35

Go to Step 26

24

Test the speed sensor circuit for a open, high resistance or short to ground between the cruise control module and Instrument Cluster. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 35

Go to Step 26

25

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 35

Go to Step 31

26

Inspect for poor connections at the harness connector of the VCM. 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 35

Go to Step 34

27

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 35

Go to Step 32

28

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 35

Go to Step 33

29

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 35

--

30

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

Did you complete the repair?

--

Go to Step 35

--

31

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

Did you complete the replacement?

--

Go to Step 35

--

32

Replace the multifunction turn signal lever. Refer to Multifunction, Turn Signal, and Hazard Switch Replacement - On Vehicle in Steering Wheel and Column - Tilt.

Did you complete the replacement?

--

Go to Step 35

--

33

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

Did you complete the replacement?

--

Go to Step 35

--

34

Important: The PCM must be reprogrammed after replacement. Refer to Powertrain Control Module Programming in Engine Controls.

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

Did you complete the replacement?

--

Go to Step 35

--

35

Operate the vehicle within the conditions for cruise control operation.

Does the cruise control system operate correctly?

--

System OK

Go to Step 2