Diagnostic Instructions
DTC Descriptors
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 output commanded on.
Conditions for Setting the DTC
P1A8B 00
42-volt circuit temperature is greater than 105°C (221°F).
P1A8B 11
42-volt circuit temperature is greater than 115°C (239°F).
P1A8C
42-volt circuit temperature is greater than 125°C (257°F).
Action Taken When the DTC Sets
P1A8B
| • | DTC P1A8B is a Type C DTC. |
| • | The HPCM stores the DTC information in memory when the diagnostic runs and fails. |
P1A8C
| • | DTC P1A8C is a Type C DTCs. |
| • | The HPCM stores the DTC information in memory when the diagnostic runs and fails. |
| • | The APM will shut down 42-volt conversion. |
Conditions for Clearing the DTC
P18AB
DTC P1A8B is a Type C DTC.
P1A8B 00
42-volt circuit temperature is less than 90°C (194°F).
P1A8B 11
42-volt circuit temperature is less than 100°C (212°F).
P1A8C
| • | DTC P1A8C is a Type C DTC. |
| • | 42-volt circuit temperature is less than 110°C (230°F). |
Diagnostic Aids
| • | DTC C0561 76 may be set. |
| • | 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 |
Reference Information
Schematic Reference
Hybrid Controls Schematics
Connector End View Reference
Component Connector End Views
Description and Operation
Drive Motor Generator Control Module Description and Operation
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References
for scan tool information
Circuit/System Verification
Inspect for DTC P0AF7.
| ⇒ | If the DTC is not set, continue to Circuit/System Testing. |
Circuit/System Testing
- Place the vehicle in Park and start the engine.
- Place the steering wheel in the centered position. Do not rotate the steering wheel.
- Observe the 42V Circuit Current parameter in the APM data list on the scan tool.
| ⇒ | If the 42V Circuit Current parameter is greater than 0.5 amps with no steering input, replace the power steering control module (PSCM). |
- Rapidly rotate the steering wheel to the left and right while observing the 42V Circuit Current parameter.
| ⇒ | If the 42V Circuit Current parameter is greater than 40 amps, replace the PSCM. |
| ⇒ | If the 42V Circuit Current parameter is less than 40 amps, replace the APM. |
Repair Instructions
Perform the
Diagnostic Repair Verification
after completing the diagnostic procedure.
Control Module References
for APM or PSCM replacement, setup, and programming
