GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC P42 Commercial Chassis 🢒 DTC 🢒 DTC P0568 Cruise Control Set Switch Circuit

Object Number: 226924 Size: MF
Engine Controls Components L57 EFI
Engine Controls (Cell 22: Fuel Controls 5)
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The cruise Set/Coast switch is an input to the fuel control portion of the PCM. These inputs allow the PCM to control and hold a requested speed. A Cruise Set/Coast switch sends an ignition voltage signal to the PCM when the Set/Coast switch is ON.

Conditions for Setting the DTC
    • The cruise switch is OFF.
    • The ignition voltage on the Resume switch signal circuit.

or

    • The cruise switch is ON.
    • The Resume switch is ON for longer than 25.5 seconds.

Action Taken When the DTC Sets
    • The PCM will not illuminate the Malfunction Indicator Lamp (MIL).
    • The PCM records the operating conditions at the time the diagnostic fails. This information stores in the Failure Records.

Conditions for Clearing the MIL/DTC
    • A History DTC will clear after forty consecutive warm-up cycles that the diagnostic does not fail (the coolant temperature has risen 5°C (40°F) from the start up coolant temperature and the engine coolant temperature exceeds 71°C (160°F) during that same ignition cycle).
    • Use of a Scan tool will clear the DTC codes.

Diagnostic Aids

If the Set/Coast switch is stuck in the ON position or the driver is holding the Set/Coast switch ON for longer than 25.5 seconds, DTC P0568 will set. DTC P0568 only checks the signal circuit for a short to voltage.

Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

  1. This step determines if the signal circuit is shorted to voltage.

    2.

  2. This step determines if the PCM or the switch is malfunctioning.

Step

Action

Value(s)

Yes

No

1

Important: Before clearing any DTCs, use the Scan Tool Capture Info to save freeze frame and failure records for reference, as the Scan Tool loses data when using the Clear Info function.

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2
  1. Connect the Scan Tool.
  2. Turn the ignition ON with the engine OFF.
  3. Turn the cruise switch OFF.

Does the Scan Tool display the Set switch ON?

--

Go to Step 3

Go to Step 4

3
  1. Turn the ignition ON.
  2. Disconnect the PCM brown 24 way connector.
  3. Probe the Set switch signal circuit at the PCM harness with a test light connected to the chassis ground.

Is the test light ON?

--

Go to Step 5

Go to Step 6

4

The DTC is intermittent. If no additional DTCs are stored, refer to Diagnostic Aids. If any additional DTCs were stored, refer to the applicable DTC table(s) first.

Are there any additional DTCs stored?

--

Go to the Applicable DTC Table

Go to Diagnostic Aids

5
  1. The Resume switch signal circuit is shorted to voltage.
  2. Repair as necessary.

Is the action complete?

--

Go to Step 8

--

6

Replace the PCM.

Important: The new PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming .

Is the action complete?

--

Go to Step 7

--

7
  1. Using the Scan Tool, clear the DTCs.
  2. Start engine and idle at normal operating temperature.
  3. Select DTC, Specific, then enter the DTC number which was set.
  4. Operate the vehicle, within the Conditions for Setting this DTC, until the Scan Tool indicates the diagnostic Ran.

Does the Scan Tool indicate the diagnostic Passed?

--

Go to Step 8

Go to Step 2

8

Does the Scan Tool display any additional undiagnosed DTCs?

--

Go to the Applicable DTC Table

System OK