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 P1A97: Starter/Generator Control Module Hybrid Battery Voltage Sense Circuit Low Voltage

DTC P1A98: Starter/Generator Control Module Hybrid Battery Voltage Sense Circuit High Voltage

Circuit/System Description

The starter/generator control module (SGCM) monitors the hybrid battery system voltage for a low and high condition to detect the failure of the 36-volt output voltage sensor that is below or above a valid range.

Conditions for Running the DTC

P1A97, P1A98

The engine is running.

Conditions for Setting the DTC

P1A97

    • Sensor signal is less than 0.2 volt for continuous 20 ms.
    • Sensor signal is less than 0.2 volt for 20 ms and 36-volt battery voltage is greater than 5 volts for 20 ms.

P1A98

Sensor output voltage less than 4 volts and 36-volt battery voltage is greater than 5 volts for 20 ms.

Action Taken When the DTC Sets

P1A97, P1A98

    • Stop PWM (MGU shutdown).
    • APM PWM off.

Conditions for Clearing the DTC

P1A97, P1A98

Closes 30 seconds after cycle wake up signal.

Diagnostic Aids

P1A97

Possible internal sensor shorted.

P1A98

Possible internal sensor 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 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. With a scan tool, clear the DTC.
  2. Ignition OFF, wait 30 seconds.
  3. Ignition ON, operate the vehicle within the Conditions for Running the DTC.
  4. If the DTC resets, replace the SGCM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for SGCM replacement, setup, and programming