P0A4B

DTC P0A4B

Diagnostic Instructions

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

DTC Descriptor

DTC P0A4B
- Starter/Generator Position Sensor Circuit

Circuit/System Description

The motor generator unit (MGU) position sensor is used for determining motor control of the MGU. The motor control consists of the angular position and speed of the MGU. The rotor is bolted on the MGU shaft, the stator is bolted on the MGU bracket and the sensor circuit is soldered on the motor control board in the starter/generator control module (SGCM). The SGCM monitors the position sensor circuit to detect a converter error (loss of speed signal or tracking).

Conditions for Running the DTC

The engine is running.

Conditions for Setting the DTC

R/D converter error (loss of signal or tracking) for 100 ms

Action Taken When the DTC Sets

Stop PWM (MGU shutdown)

Conditions for Clearing the DTC

Clears 30 seconds after cycle wake up signal.

Diagnostic Aids

* Possible sensor cable short to ground, short to voltage or open
* Possible MGU or SGCM fault
* Possible wiring harness fault

Circuit/System Testing

Caution: To help avoid personal injury, additional precautions must be taken prior to working on the generator control module or the generator starter. After removing the 36V battery cables from the generator battery, remove both engine wiring harness connectors from the generator control module. Wait at least 5 minutes and then remove the generator control module cover. Verify voltage levels at all 36V, 12V, and 3-phase connections, are less than 3 volts using a DMM before proceeding.

1. Disconnect the MGU X2 and the SGCM X2 connectors.
2. Test the circuits in the SGCM to MGU Terminal Reference Table as indicated below. Also check these circuits for short to ground.

^ If any of the circuits are not within specification, check for an open/high resistance or short to ground.

3. Reconnect SGCM connector X2.
4. Test the circuits in the MGU to SGCM Specification Table to ground as indicated below.

^ If any of the circuits are not within the specified range, replace the SGCM.

5. Reconnect the MGU X2 connector and disconnect the SGCM X2 connector. Refer to Generator with Starter Replacement and Generator Control Module Replacement.
6. Test the circuits in the SGCM to MGU Specification Table as indicated below.

^ If all circuits test normal, replace the MGU.














Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

* Generator with Starter Replacement for MGU replacement