P12A8

DTC P12A8

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

* Review Strategy Based Diagnosis Strategy Based Diagnosis for a overview of the diagnostic approach.

* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors

DTC P12A8
- Fuel Pump Control Signal Message Counter Incorrect

Circuit/System Description

The fuel pump power control module is constantly sending serial data messages to the ECM regarding the operating state of the fuel pump power control system. These messages are sent in a continuously repeating series of rolling counts with associated password protect samples and each count/sample is assigned a value. When the ECM determines that too many of the counts/samples contain an error value, the ECM sets DTC P12A8.

Conditions for Running the DTC

* The ignition voltage is greater than 9 V.

* The engine run time is greater than 0.5 s.

* No other CAN errors are present.

* The DTC runs continuously when the above conditions are met.

Conditions for Setting the DTC

The ECM detects that 64 of 80 counts/samples contain an error value.

Action Taken When the DTC Sets

DTC P12A8 is a Type A DTC.

Conditions for Clearing the DTC

DTC P12A8 is a Type A DTC.

Diagnostic Aids

An intermittent fault in the CAN circuits will cause the ECM to set DTC P12A8.

Reference Information

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References Control Module References for scan tool information

Circuit/System Verification

Note:

* DTC P12A8 is an informational DTC.

* Diagnose all other engine control module DTCs prior to DTC P12A8.

1. Verify there are no other engine control module or communication DTCs set.

• If a DTC is set
Refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle

• If a DTC is not set

2. Complete the diagnosis by looking for an intermittent CAN circuit fault. Refer to Scan Tool Does Not Communicate with High Speed GMLAN Device Scan Tool Does Not Communicate with High Speed GMLAN Device.

• If an intermittent CAN circuit fault is found
Refer to Circuit/System Testing.

• If an intermittent CAN circuit fault is not found

3. All OK.

Circuit/System Testing

1. Verify that no other DTCs are set except for DTC P12A8.

• If any other DTCs are set
Refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle.

• If only DTC P12A8 is set

2. Replace the K27 Fuel Pump Power Control Module.

3. Verify the DTC does not set while operating the vehicle within the Conditions for Running the DTC.

• If DTC sets
Replace the K20 Engine Control Module.

• If DTC does not set

4. All OK.

Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests after completing the repair.

* Fuel Pump Power Control Module Replacement Fuel Pump Power Control Module Replacement

* Control Module References Control Module References for Engine Control Module replacement, programming, and setup.