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For 1990-2009 cars only

DTC P0568 8.1L

Circuit Description

The cruise control set/coast switch is an input to the throttle actuator control (TAC) module. The TAC module uses the cruise control set/coast switch signal circuit in order to detect when the driver has requested to set the vehicle speed or to decelerate the vehicle speed. The TAC module detects a voltage signal on the cruise control set/coast switch signal circuit when the switch is applied. The TAC module sends a serial data signal to the powertrain control module (PCM) via the serial data circuit. This DTC sets if the PCM receives a serial data signal from the TAC module indicating that voltage is present on the cruise control set/coast switch signal circuit for longer than 90 seconds.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0568 (8.1L) Cruise Control Set Switch Circuit

Conditions for Running the DTC

    • The ignition is ON.
    • The cruise control switch is ON.

Conditions for Setting the DTC

The PCM receives a serial data signal from the TAC module indicating that the set/coast switch is ON for longer than 90 seconds.

Action Taken When the DTC Sets

    • The PCM stores the DTC information into memory when the diagnostic runs and fails.
    • The malfunction indicator lamp (MIL) will not illuminate.
    • The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records.
    • The cruise control system is disabled.

Conditions for Clearing the MIL/DTC

    • A last test failed, or the current DTC, clears when the diagnostic runs and does not fail.
    • A history DTC clears after 40 consecutive warm-up cycles, if failures are not reported by this or any other emission related diagnostic.
    • Use a scan tool in order to clear the MIL/DTC.

Diagnostic Aids

Ensure that the set/coast switch is not stuck or sticking in the engaged position.

For an intermittent condition, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Test Description

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

  1. This step determines if a condition is present.

Step

Action

Yes

No

Schematic Reference : Cruise Control Schematics

Connector End View Reference: Powertrain Control Module Connector End Views in Engine Controls - 8.1L

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. 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 Set/Coast Switch parameter in the powertrain control module (PCM) data list.

Does the Cruise Set/Coast Switch parameter display On?

Go to Step 3

Go to Diagnostic Aids

3

  1. Turn OFF the ignition.
  2. Disconnect the cruise control switch.
  3. Turn ON the ignition, with the engine OFF.
  4. With the scan tool, observe the Cruise Set/Coast Switch parameter in the PCM data list.

Does the Cruise Set/Coast Switch parameter display On?

Go to Step 4

Go to Step 5

4

Test the cruise control set/coast 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 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 and Connector Repairs in Wiring Systems.

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 throttle actuator control (TAC) 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 9

Go to Step 7

7

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

Did you complete the replacement?

Go to Step 9

--

8

Replace the cruise control switch. Refer to Turn Signal Multifunction Switch Replacement in Steering Wheel and Column.

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 Running the DTC.

Does the DTC reset?

Go to Step 2

System OK

DTC P0568 6.6L and 7.8L

Circuit Description

The cruise control set/coast switch is an input to the engine control module (ECM). The ECM monitors the cruise control set/coast switch signal circuit in order to detect when the driver has requested to set the vehicle speed or to allow the vehicle to coast. The ECM detects a voltage signal on the cruise control set/coast switch signal circuit when the switch is applied. This DTC sets if the ECM detects that voltage is present on the cruise control set/coast switch signal circuit for longer than 90 seconds.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0568 (6.6L and 7.8L) Cruise Control Set Switch Circuit

Conditions for Running the DTC

    • The ignition is ON.
    • The cruise switch is ON.

Conditions for Setting the DTC

The ECM detects the set/coast switch is ON for longer than 90 seconds.

Action Taken When the DTC Sets

    • The ECM stores the DTC information into memory when the diagnostic runs and fails.
    • The malfunction indicator lamp (MIL) will not illuminate.
    • The ECM records the operating conditions at the time the diagnostic fails. The ECM stores this information in the Failure Records.
    • The cruise is disabled.

Conditions for Clearing the MIL/DTC

    • A last test failed, or the current DTC, clears when the diagnostic runs and does not fail.
    • A history DTC clears after 40 consecutive warm-up cycles, if failures are not reported by this or any other emission related diagnostic.
    • Use a scan tool in order to clear the MIL/DTC.

Diagnostic Aids

    • Inspect for a set/coast switch stuck in the engaged position or the signal circuit is shorted to voltage.
    • For an intermittent, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Test Description

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

  1. This step determines if a condition is present.

Step

Action

Yes

No

Schematic Reference: Cruise Control Schematics

Connector End View Reference: Engine Control Module Connector End Views in Engine Controls - 6.6L (LLY), or Engine Control Module Connector End Views in Engine Controls - 7.8L

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. 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 Set/Coast Switch parameter in the powertrain control module (PCM) Engine 1 Data, data list.

Does the Cruise Set/Coast Switch parameter display On?

Go to Step 3

Go to Diagnostic Aids

3

  1. Turn OFF the ignition.
  2. Disconnect C1 of the engine control module (ECM).
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a test lamp between the cruise control set/coast switch signal circuit and a good ground.

Does the test lamp illuminate?

Go to Step 4

Go to Step 6

4

Test the cruise control set/coast 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 9

Go to Step 5

5

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 9

Go to Step 7

6

Inspect for poor connections at the harness connector of the ECM. 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 9

Go to Step 8

7

Replace the cruise control switch. Refer to Turn Signal Multifunction Switch Replacement in Steering Wheel and Column.

Did you complete the replacement?

Go to Step 9

--

8

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

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 Running the DTC.

Does the DTC reset?

Go to Step 2

System OK