Buick Regal Owners & Service Manuals

Buick Regal: DTC P12A6

Diagnostic Instructions

  • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
  • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
  • Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC P12A6

Fuel Pump Driver Control Module Enable Circuit Performance

Diagnostic Fault Information

Engine Controls and Fuel - 2.0L (LTG)

Circuit/System Description

The engine control module (ECM) provides ignition voltage to the fuel pump driver control module whenever the engine is cranking or running. The control module enables the fuel pump driver control module as long as the engine is cranking or running, and ignition system reference pulses are received.

While this enable voltage is being received, the fuel pump driver control module supplies a varying voltage to the in-tank fuel pump module in order to maintain the desired fuel line pressure.

Conditions for Running the DTC

  • The ignition voltage is greater than 7 V.
  • The DTC runs continuously when the condition above is met.

Conditions for Setting the DTC

The ECM state of the fuel pump enable circuit does not match the state of the fuel pump enable circuit sensed by the fuel pump driver control module for 0.5 s.

Action Taken When the DTC Sets

DTC P12A6 is a Type A DTC.

Conditions for Clearing the DTC

DTC P12A6 is a Type A DTC.

Reference Information

Schematic Reference

Engine Controls Wiring Schematics (LTG)

Connector End View Reference

Component Connector End View Index

Description and Operation

Fuel System Description

Electrical Information Reference

  • Circuit Testing
  • Connector Repairs
  • Testing for Intermittent Conditions and Poor Connections
  • Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Ignition ON.

2. Verify that DTC P12A6 is not set.

  • If the DTC is set

Refer to Circuit/System Testing.

  • Go to next step: If the DTC is not set

3. Verify the parameters listed below do not display Malfunction when commanding the Fuel Pump Enable On and Off with a scan tool.

  • Fuel Pump Enable Circuit Low Voltage Test Status
  • Fuel Pump Enable Circuit Open Test Status
  • Fuel Pump Enable Circuit High Voltage Test Status
  • If Malfunction is displayed

Refer to Circuit/System Testing.

  • Go to next step: If Malfunction is not displayed

4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

5. Verify the DTC does not set.

  • If the DTC sets

Refer to Circuit/System Testing.

  • Go to next step: If the DTC does not set

6. All OK.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the K111 Fuel Pump Driver Control Module.

2. Ignition ON for 10 s.

3. Verify that a test lamp does not illuminate between the control circuit terminal 2 and ground.

  • If the test lamp illuminates
  1. Ignition OFF, remove the test lamp, disconnect the harness connector at the K20 Engine Control Module, ignition ON.
  2. Test for less than 1 V between the control circuit and ground.
    • If 1 V or greater, repair the short to voltage on the circuit.
    • If less than 1 V, replace the K20 Engine Control Module.
  • Go to next step: If the test lamp does not illuminate

4. Remove the test lamp.

5. Verify the scan tool Fuel Pump Enable Circuit Low Voltage Test Status parameter is OK when commanding the Fuel Pump Enable On with a scan tool.

  • If OK is not displayed
  1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module.
  2. Test for infinite resistance between the control circuit and ground.
    • If less than infinite resistance, repair the short to ground on the circuit.
    • If infinite resistance, replace the K20 Engine Control Module.
  • Go to next step: If OK is displayed

6. Install a 3 A fused jumper wire between the control circuit terminal 2 and ground.

7. Verify the scan tool Fuel Pump Enable Circuit Low Voltage Test Status parameter is Malfunction when commanding the Fuel Pump Enable On with a scan tool.

If Malfunction is not displayed

  1. Ignition OFF, remove the jumper wire, disconnect the harness connector at the K20 Engine Control Module.
  2. Test for less than 2 Ω in the control circuit end to end.
    • If 2 Ω or greater, repair the open/high resistance in the circuit.
    • If less than 2 Ω, replace the K20 Engine Control Module.

Go to next step: If Malfunction is displayed

8. Replace the K111 Fuel Pump Driver Control Module.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  • Fuel Pump Power Control Module Replacement (AWD) or Fuel Pump Power Control Module Replacement (FWD)
  • Control Module References for ECM replacement, setup, and programming

DTC P135A

Diagnostic Instructions

  • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
  • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
  • Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC P135A

Ignition Coil Supply Voltage Circuit Bank 1

Diagnostic Fault Information

Engine Controls and Fuel - 2.0L (LTG)

Circuit/System Description

The ignition system uses an individual ignition coil for each cylinder. The engine control module (ECM) monitors the ignition voltage from the fuse to the individual coils.

Conditions for Running the DTC

  • Delay starting at ignition On for 5 engine revolutions.
  • Ignition Run/Crank relay voltage is greater than 5 V
  • PT relay voltage is greater than 11 V

The DTC runs continuously when the above conditions are met.

Conditions for Setting the DTC

The ECM detects less than 2.5 V on the ignition coil supply voltage circuit.

Action Taken When the DTC Sets

DTC P135A is a Type B DTC.

Conditions for Clearing the DTC

DTC P135A is a Type B DTC.

Reference Information

Schematic Reference

Engine Controls Wiring Schematics (LTG)

Connector End View Reference

Component Connector End View Index

Description and Operation

Electronic Ignition System Description

Electrical Information Reference

  • Circuit Testing
  • Connector Repairs
  • Testing for Intermittent Conditions and Poor Connections
  • Wiring Repairs

Scan Tool Reference

Control Module References

Circuit/System Verification

1. Ignition ON.

2. Verify the scan tool Ignition Coil Supply Voltage parameter displays ON.

  • If ON is not displayed

Refer to Circuit/System Testing.

  • Go to next step: If ON is displayed

3. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

4. Verify the DTC does not set.

  • If the DTC sets

Refer to Circuit/System Testing.

  • Go to next step: If the DTC does not set

5. All OK.

Circuit/System Testing

1. Ignition OFF, disconnect the X1 harness connector at the K20 Engine Control Module.

2. Connect a 3 A fused jumper wire between the control circuit terminal 67 and ground, ignition ON.

3. Verify a test lamp illuminates between the ignition circuit terminal 51 and ground.

  • If the test lamp does not illuminate and the circuit fuse is good
  1. Ignition OFF, remove the test lamp.
  2. Test for less than 2 Ω in the ignition circuit end to end.
    • If 2 Ω or greater, repair the open/high resistance in the circuit.
    • If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.
  • If the test lamp does not illuminate and the circuit fuse is open

NOTE: The ignition circuit may supply voltage to other components.

Make sure to test all circuits and components for a short to ground that share the ignition circuit.

  1. Ignition OFF, remove the test lamp, and disconnect all components on the circuit.
  2. Test for infinite resistance between the ignition circuit and ground.
    • If less than infinite resistance, repair the short to ground on the circuit.
    • Go to next step: If infinite resistance
  3. Replace the fuse, ignition ON.
  4. Verify the fuse is good after connecting each of the components one at a time.
    • If the fuse opens, replace the component that opens the fuse when connected.
    • If the fuse is good, all OK.
  • Go to next step: If the test lamp illuminates

4. Replace the K20 Engine Control Module.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

  • Ignition Coil Replacement
  • Control Module References for engine control module replacement, programming, and setup

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