P1A21

DTC P1A21

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 P1A21
- Hybrid Battery Contactor Control Sequence Incorrect

Circuit/System Description

The hybrid powertrain control module (HPCM) controls the operation of the high voltage (HV) contactor relays through communication with the battery energy control module (BECM). The HPCM utilizes a pulse width modulated (PWM) circuit and a redundant GM LAN message to command the HV contactor relays Open and Closed. Under normal operating conditions, the BECM opens and closes the HV contactor relays based only upon the HPCM command. This diagnostic identifies when the BECM has opened the HV contactor relays when the HPCM is commanding them closed.

Conditions for Running the DTC

* The vehicle power mode is RUN.
* Accessory voltage is 9-18 volts.
* The vehicle has passed a successful precharge and the High Voltage contactor relays have been closed this ignition.
* The HPCM is commanding the BECM to keep the HV contactor relays closed.

Conditions for Setting the DTC

The BECM reports that the contactor relays are open.

Action Taken When the DTC Sets

DTC P1A21 is a Type A DTC.

Conditions for Clearing the DTC

DTC P1A21 is a Type A DTC.

Diagnostic Aids

The BECM will set contactor status to OPEN when the PWM duty cycle is 65-75 percent. The BECM will set contactor status to CLOSED when the PWM duty cycle is 25-35 percent. The BECM will set contactor status to INVALID when the PWM duty cycle is out of the ranges specified for open and closed. The frequency of the PWM signal must be between 247 Hz to 253 Hz to be valid.

Circuit/System Verification

1. Ignition ON, observe the DTC information with a scan tool. DTC P1A21 should not set.
2. Ignition ON, with a scan tool the monitor hybrid battery contactor commanded PWM. The contactor commanded PWM should be 30 percent.
3. Operate the vehicle within the Conditions for Running the DTCs. You may also operate the vehicle within the conditions that you observed from the Freeze Fame/Failure Records data.

Circuit/System Testing

Verify that DTCs P1AE4, P0A80, P1ABE, or P1A0C are not set.

If any of the listed DTCs are set, repair them first. Refer to Diagnostic Trouble Code (DTC) List - Vehicle. Diagnostic Trouble Code Descriptions
If all circuits test normal, replace the BECM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair. Verification Tests