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 P0A38: Starter/Generator Temperature Sensor Circuit Low Voltage

DTC P0A39: Starter/Generator Temperature Sensor Circuit High Voltage

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Signal

P0A38

P0A39

P0A39

--

Low reference

--

P0A39

--

--

Circuit/System Description

The starter/generator control module (SGCM) monitors to detect if the motor generator temperature sensor is shorted to ground, shorted to voltage or open.

Conditions for Running the DTC

The engine is running.

Conditions for Setting the DTC

P0A38

    • Sensor output voltage less than 0.2 volt for 1 second.
    • Temperature is greater than 215°C (419°F) for 1 second.

P0A39

    • Sensor output voltage greater than 3.95 volts for 1 second.
    • Temperature is less than -20°C (-4°F) for 1 second.

Action Taken When the DTC Sets

P0A38, P0A39

Hybrid system torque will be limited to 50 percent

Conditions for Clearing the DTC

P0A38, P0A39

The MGU temperature sensor returns normal range for 10 seconds

Diagnostic Aids

P0A38

Possible internal temperature sensor signal circuit short to ground.

P0A39

Possible internal temperature sensor signal circuit short to voltage or open.

Reference Information

Schematic Reference

Hybrid Controls Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Starter/Generator 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

Circuit/System Testing

  1. Ignition OFF, disconnect harness connectors from the SGCM. Refer to Generator Control Module Replacement.
  2. Test for 120-125 k ohms between the signal circuit SGCM X2 terminal 2 and the low reference circuit X2 terminal 14.
  3. If not within the specified range , test the signal circuit for short to ground or the signal circuit shorted to the low reference circuit.
    If the circuits test normal, replace the SGCM.
  4. Disconnect the connectors at the MGU. Refer to Generator with Starter Replacement.
  5. Test for less than 1 ohm between the SGCM X2 connector terminal 2 and the MGU X1 connector terminal G.
  6. If greater than the specified value, test the signal circuit for an open/high resistance or short to voltage.
  7. Test for less than 1 ohm between SGCM X2 connector terminal 14 and the MGU X1 connector terminal F.
  8. If greater than the specified value, repair the open/high resistance.
  9. If circuits test normal, replace the MGU.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Generator with Starter Replacement for MGU replacement
    •  Control Module References for SGCM replacement, setup, and programming