P1A59

DTC P1A59

Diagnostic Instructions

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



DTC Descriptor
DTC P1A59
- Hybrid Battery Pack Voltage




Circuit/System Description

The engine control module (ECM) monitors while deviation of the voltage across the battery pack is checked using the 3 module voltage sensors. If one module within the battery pack is not within the expected value, it will manifest itself in a high Delta V SOH (state of health).


Conditions for Running the DTC

The engine is running.


Conditions for Setting the DTC

Maximum module voltage - minimum module voltage is greater than 0.75 volts for 6 seconds.


Action Taken When the DTC Sets

The hybrid system is disabled.


Conditions for Clearing the DTC

Module voltage deviation returns to less than or equal to 0.75 volts.


Reference Information
Schematic Reference

Hybrid Energy Storage Schematics ()
Connector End View Reference

Component Connector End Views (Connector Views)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information
Special Tools

J 35616 GM Approved Terminal Test Kit


Circuit/System Verification

Observe the scan tool BECM Hybrid Battery 1, Hybrid Battery 2 and Hybrid Battery 3 parameters while road testing the vehicle. The voltage difference between the battery voltages should be within 0.75 volts.


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.


Caution: 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.


Important: In order to avoid damaging BECM X1 and X2 connector terminals, the proper test probes should be used. The proper test probes are as follows:



* J-35616-65B for female terminals
* J-35616-64B for male terminals


1. Verify the DTC is set as current.
2. Measure the voltage of each battery module, the voltages should be within 1.0 volt.

• If greater than specified value, replace the battery pack.

3. Disconnect harness connector X1 from the BECM. Refer to Hybrid Battery Service Disconnect/Connect ().
4. Test for 1.3-1.7k ohms between the following circuits.

* X1 terminal 1 to ring terminal 7
* X1 terminal 11 to ring terminal 6
* X1 terminal 2 to ring terminal 5
* X1 terminal 12 to ring terminal 4


• If not within specified range, replace the voltage sensor harness assembly.

5. If all circuits test normal, replace the BECM.



Repair Instructions

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

* Generator Battery Temperature Sensor Wiring Harness Replacement ()
* Generator Battery Replacement ()
* Control Module References (Programming and Relearning) for BECM replacement, setup, and programming