Buick Regal: Malfunction Indicator Lamp (MIL) Diagnosis

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.

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.

Diagnostic Aids

If the condition is intermittent, move the related harnesses and connectors while monitoring the scan tool MIL control circuit status parameters. Perform this test with the ignition ON and the engine OFF, and with the engine running. The MIL control circuit status parameters change from OK or Not Run to Malfunction if there is a condition with a circuit or a connection.

Reference Information

Schematic Reference

• Engine Controls Wiring Schematics (LTG)
• Instrument Cluster Wiring Schematics

Connector End View Reference

Component Connector End View Index

Electrical Information Reference

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

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

NOTE: Any MIL requesting DTCs that may be set should be diagnosed first.

1. Ignition ON.

2. Verify the parameters listed below do not display Malfunction when commanding the Malfunction Indicator Lamp On and Off with a scan tool.

• The MIL Control Circuit Low Voltage Test Status
• The MIL Control Circuit Open Test Status
• The MIL Control Circuit High Voltage Test Status
• If Malfunction is displayed

Refer to Circuit/System Testing.

• Go to next step: If Malfunction is not displayed

3. Engine running.

4. Verify the parameters listed below do not display Malfunction when commanding the Malfunction Indicator Lamp On and Off with a scan tool.

• The MIL Control Circuit Low Voltage Test Status
• The MIL Control Circuit Open Test Status
• The MIL Control Circuit High Voltage Test Status
• If Malfunction is displayed

Refer to Circuit/System Testing.

• Go to next step: If Malfunction is not displayed

5. Verify the malfunction indicator lamp turns ON and OFF when commanding the Malfunction Indicator Lamp On and Off with a scan tool.

• If the malfunction indicator lamp does not turn ON and OFF

Refer to Circuit/System Testing.

• Go to next step: If the malfunction indicator lamp turns ON and OFF

6. All OK.

Circuit/System Testing

1. Ignition OFF.

2. Disconnect the X1 harness connector at the K20 Engine Control Module.

3. Ignition ON, verify the malfunction indicator lamp does not illuminate.

• If the malfunction indicator lamp illuminates

1. Test for infinite resistance between the control circuit terminal X1 71 and ground.
   • If less than infinite resistance, repair the short to ground in the circuit.
   • If infinite resistance, replace the P16 Instrument Cluster.

• Go to next step: If the malfunction indicator lamp does not illuminate

4. Connect a 3 A fused jumper wire between the control circuit terminal X1 71 and ground.

5. Verify the malfunction indicator lamp illuminates.

• If the malfunction indicator lamp illuminates

Replace the K20 Engine Control Module.

• If the malfunction indicator lamp does not illuminate

1. Test for less than 1 V between the control circuit terminal X1 71 and ground.
   • If 1 V or greater, repair the short to voltage on the circuit.
   • Go to next step: If less than 1 V
2. Ignition OFF.
3. 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.
   • Go to next step: If less than 2 Ω.

6. Ignition OFF, disconnect the X1 harness connector at the instrument cluster.

7. Ignition ON, verify a test lamp illuminates between the ignition voltage circuit terminal 8 and ground.

• If the test lamp does not illuminate and the circuit fuse is open

1. Ignition OFF.
2. Test for infinite resistance between the ignition voltage circuit and ground.
   • If less than infinite resistance, repair the short to ground on the circuit.

• If the test lamp does not illuminate and the circuit fuse is good

1. Ignition OFF.
2. Test for less than 2 Ω in the ignition voltage circuit end to end.
   • If 2 Ω or greater, repair the open/high resistance in the circuit.

• Go to next step: If the test lamp illuminates

8. Replace the P16 Instrument Cluster.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

• Instrument Cluster Replacement
• Control Module References for control module replacement. programming, and setup

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