GM Service Manual Online
For 1990-2009 cars only

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 Descriptors

DTC P0A84: Hybrid Battery Pack Cooling Fan Control Circuit Low Voltage

DTC P0A85: Hybrid Battery Pack Cooling Fan Control Circuit High Voltage

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Cooling fan tach feedback

P0A84

P0A84

P0A85

P0A84, P0A85

Circuit/System Description

The battery energy control module (BECM) monitors the cooling fan tach circuit to detect if the fan speed is slower or faster than the commanded state. If a failure is detected, the appropriate DTC will set.

Conditions for Running the DTC

The engine is running.

Conditions for Setting the DTC

P0A84

    • Fan control feedback is less than 5 percent.
    • Fan state is ON.

P0A85

    • Fan control feedback is greater than 95 percent.
    • Fan state is ON.
    • Fan command is less than 80 percent.

Action Taken When the DTC Sets

The hybrid system is not affected.

Conditions for Clearing the DTC

The fan speed control feedback is normal.

Reference Information

Schematic Reference

Hybrid Cooling Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Starter Generator Control Module Cooling System Description and Operation

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

Special Tools

J 35616 GM Approved Terminal Test Kit

Circuit/System Verification

Warning: To help avoid personal injury, be careful when working in the vicinity of the generator battery disconnect control module. Internal components will still be live, 36V potential, even when the cover has been opened or removed.

  1. Verify the DTC is set current, clear the DTC.
  2. Ignition ON, using the scan tool special function command the hybrid cooling fan ON and OFF several times.
  3. If the hybrid battery pack cooling fan operates as commanded and the DTC resets, continue with Circuit/System Testing.
    If the hybrid pack cooling fan does not operate as commanded , replace the hybrid battery pack cooling fan.

Circuit/System Testing

Note: In order to avoid damaging BECM X1 and X2 connector terminals, the proper test probes should be used. The proper test probes are as follows:

    • J-35616-65B for female terminals
    • J-35616-64B for male terminals
  1. Ignition OFF, disconnect the cooling fan harness connector. Refer to Hybrid Battery Service Disconnect/Connect.
  2. Disconnect BECM harness connector X2.
  3. Test the fan tach feedback circuit X2 connector terminal 11 to cooling fan harness connector terminal 4 for a short to voltage or a short to ground.
  4. If the circuit test normal replace the BECM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Generator Battery Vent Fan Replacement
    •  Control Module References for BECM replacement, setup, and programming