P1EF7 – Battery Charger Control Module Ignition On/Start Switch Circuit High Voltage (GM)

By Reinier (Contact Me)
Last Updated 2023-10-02
Automobile Repair Shop Owner

Manufacturer Specific Definitions for P1EF7

Table of Contents

1. What Does Code P1EF7 Mean?
2. Where is the P1EF7 sensor located?
3. What are the common causes of code P1EF7?
4. What are the symptoms of code P1EF7?
5. Get Help with P1EF7

What Does Code P1EF7 Mean?

WARNING: The information provided here is intended to be purely informational to non-professional mechanics and, it should therefore NOT be used as the basis for attempts to diagnose the causes of trouble code P1EF7 or ANY other trouble codes that are related to code P01EF7. The potential to suffer serious or even fatal electrocution while working on hybrid vehicles is extremely high, so be sure to seek professional assistance from suitably qualified and certified persons to diagnose and resolve trouble code P1EF7 and its related codes.  

OBD II fault code P1EF7  is a manufacturer-specific trouble code that is defined by carmaker Chevrolet as P1EF7 – “Battery Charger Control Module Ignition On/Start Switch Circuit High Voltage “  and is set on Chevrolet hybrid models when the BCM (Body Control Module) detects an abnormally high voltage or current in the system that controls the starting circuits of the vehicle’s internal combustion engine.

Since the internal combustion engines on most hybrid hybrids do not have conventional starter motors anymore, the engine is rotated by the MG (Motor Generator) until it starts and runs smoothly. However, this starting system is fairly complicated, and several enabling conditions must be met or satisfied before the BCM will activate the engine’s starting circuits.

We need not delve into the complexities of these enabling conditions here, but suffice it to say that the BCM controls the engine’s starting circuits. Thus, when all required enabling conditions are met, the BCM applies a current to the engine’s starting relay when the vehicle’s power mode status is “ON”, or when the vehicle is in Service Mode.

In practice, the hybrid power train’s control module #2 monitors the status of the vehicle power mode, and when all enabling conditions are met, the start signal is transmitted via a high-speed serial communications network to the-

• battery charger control module
• A/C compressor
• battery energy control module
• fuel pump control module

–  and the Transmission Control Module (TCM). It is worth pointing out that the battery charger control module is perhaps the most important of the components/systems listed above because while control module #2 is the host control module that records and stores trouble codes originating in many hybrid systems, control module #2 does not have diagnostic abilities.

As a matter of priority, the battery charger control module has the ability to run diagnostic tests not only on the high-voltage battery pack but also on the internal combustion engine’s starting circuits. These tests involve monitoring the HV battery pack’s internal temperature and the flow of currents and voltages throughout the battery pack.

From the above, it should be clear that if defects or malfunctions exist in the HV battery pack’s circuits and internals, starting the engine could potentially cause serious damage to the HV battery and its overall charging system. Thus, in the context of trouble code P1EF7, the battery charger control module monitors all relevant circuits for abnormal voltages and currents,and when it detects an abnormal voltage or current, such as might be caused by a short circuit to B+ (battery positive) in the system, it will set code P1EF7.

Note that while the battery control module will set code P1EF7 when it detects an abnormal voltage or current three consecutive times, it will not take any kind of action, such as disabling the internal combustion engine’s starting circuits. Nonetheless, the battery charger control module will set multiple additional trouble codes at the same time as setting P1EF7, one or more of which may initiate actions that could prevent the engine from starting, depending on the nature of the problem.

Where is the P1EF7 sensor located?

This image shows the location (arrowed) of the motor/generator in the transaxle of a 2016 Chevrolet Volt hybrid that serves as both a starter motor and a traction motor to propel the vehicle.

Be aware that this transaxle does not contain any user-serviceable parts and therefore, no attempt should be made to access any of the transaxle’s internal parts by persons who are not trained, qualified, and certified to perform repairs on Chevrolet hybrid vehicles.

What are the common causes of code P1EF7?

The causes of trouble code P1EF7 could be many and varied, but could include one or more of the following-

• Defective, corrupted, or malfunctioning control module #2
• Damaged, shorted, disconnected, burnt, or corroded wiring or electrical connector in the wiring harness associated with control module #2
• Control module #2 is active when it should not be
• The vehicle power mode status is “OFF”
• Ignition output is not active, and a short circuit to battery positive is detected three consecutive times

What are the symptoms of code P1EF7?

Common symptoms of trouble code P1EF7 could include the following-

• Stored trouble code and possibly an illuminated warning light
• Depending on both the vehicle and the nature of the problem, the following additional trouble codes may be present along with P1EF7 – P15B9, P15BA, P1A5E, P1A5F, P1EF6, P1EF7, P2534 or P2535
• The vehicle may not power “ON” or crank the engine

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