P1A8B

DTC P1A8B or P1A8C

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 P1A8B 00
- 42 Volt Inverter Temperature High

DTC P1A8B 11
- 42 Volt Inverter Temperature High

DTC P1A8C
- 42 Volt Inverter Overtemperature

Circuit/System Description

The Accessory Power Module (APM) controls the energy flowing between the high voltage (300 volt) direct current (DC) and intermediate voltage (42 volt) DC to support the Electric Power Steering (EPS). The APM receives a 42 volt enable command from the Hybrid Powertrain Control Module (HPCM) over the high speed hybrid GMLAN communication circuit. APM functions will run only when the APM Enable is active on the high speed hybrid GMLAN communication circuit.

Heat is generated in the 42 volt APM circuit solely through the demand for use of the EPS. The Engine Control Module (ECM) measures the temperature of the Power Electronics Cooling Loop and commands the flow of 2 electrical coolant pumps. The APM transfers heat in the 42 volt circuit to the APM Heat Plate which is then dissipated at the Power Electronics Front End Heat Exchanger.

Based on the severity of an overheat condition in the 42 volt circuit, the APM will make decisions ranging from notification of an over temperature condition to the EPS to completely shutting down the 42 volt power conversion.

Conditions for Running the DTC

APM 42 volt enable message active.

Conditions for Setting the DTC

* DTC P1A8B 00 - 42 volt circuit temperature is greater than 105°C (221°F).
* DTC P1A8B 11 - 42 volt circuit temperature is greater than 115°C (239°F).
* DTC P1A8C - 42 volt circuit temperature is greater than 125°C (257°F).

Action Taken When the DTC Sets

* The HPCM stores the DTC information in memory when the diagnostic runs and fails.
* DTC P1A8C - the APM will shut down 42 volt conversion.

Conditions for Clearing the DTC

* DTC P1A8B 00 - 42 volt circuit temperature is less than 90°C (194°F).
* DTC P1A8B 11 - 42 volt circuit temperature is less than 100°C (212°F).
* DTC P1A8C - 42 volt circuit temperature is less than 110°C (230°F).

Diagnostic Aids

This DTC could be caused by a possible power electronics cooling system failure due to the following:

* Restricted radiator air flow or coolant fans inoperative.
* Restricted power electronics coolant flow or contaminated coolant.
* Inoperative power electronics cooling system water pump.

Circuit/System Verification

1. Verify that the ECM is commanding the electronics cooling pumps correctly.
2. Verify that the electronics cooling flow is OK.
3. Verify that the 42 volt temperature circuit in the APM is reading correctly.
4. Verify that the EPS system is not drawing excessive (> 40 Amps) 42 volt current or 42 volt current continuously.

Circuit/System Testing

1. Start the engine.
2. While stationary (vehicle not moving), rotate the steering wheel rapidly left and right and observe the 42 volt Current and 42 volt Temperature.

Repair Instructions

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