GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The cruise control switch is an input to the engine control module (ECM). The ECM monitors the cruise control switch signal circuit in order to detect when a cruise control function has been requested. The ECM detects a specific voltage signal on the cruise control set/coast and resume/accelerate switch signal circuit when a cruise control function switch is activated, with each switch having a different predetermined voltage value.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0568 Cruise Control Set Switch Circuit

Conditions for Setting the DTC

    • The engine is running.
    • Battery voltage is greater than 7.9956 voltage.
    • The ECM detects the switch is switching too quickly or stuck for too long.

Action Taken When the DTC Sets

    • The malfunction indicator lamp (MIL) will not illuminate.
    • The ECM will record operating conditions at the time the diagnostic fail. This information will be stored in the Freeze Frame and Failure Records buffers.
    •  A history DTC is stored.
    • The A/C compressor operation will be disabled while the low voltage indication exists.

Conditions for Clearing the MIL/DTC

    • A history DTC will clear after 40 consecutive warm-up cycles without a fault.
    • DTCs can be cleared by using the scan tool.
    • Disconnecting the ECM battery feed for more than 10 seconds

Diagnostic Aids

Perform the following in order to avoid misdiagnosis:

    • Rotate the steering wheel to both steering stops and activate each cruise control switch separately. With a scan tool, observe the associated cruise control switch parameter. This will help eliminate the possibility of an internally open or shorted contact coil.
    • Ensure that the resume/accel switch is not stuck or sticking in the engaged position.

Test Description

The number below refers to the step number on the diagnostic table.

  1. This step determines if condition is present.

Step

Action

Yes

No

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

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

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

Go to Step 3

Go to Diagnostic Aids

3

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

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

Go to Step 4

Go to Step 5

4

Test the cruise control resume/accel switch signal circuit for a short to voltage.

Did you find and correct the condition?

Go to Step 9

Go to Step 6

5

Inspect for poor connections at the harness connector of the cruise control switch. Refer to Testing for Intermittent Conditions and Poor Connections .

Did you find and correct the condition?

Go to Step 9

Go to Step 8

6

Inspect for poor connections at the harness connector of the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections .

Did you find and correct the condition?

Go to Step 9

Go to Step 7

7

Replace the ECM. Refer to Control Module References for ECM replacement, setup, and programming.

Did you complete the replacement?

Go to Step 9

--

8

Replace the cruise control switch.

Did you complete the replacement?

Go to Step 9

--

9

  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Setting the DTC.

Does the DTC reset?

Go to Step 2

System OK