AutoCodes – GMC – P0C78 GMC

P0C78 GMC Code - Hybrid/EV Battery System Precharge Time Too Long

Quick Answer

The hybrid battery system voltage is controlled by two high voltage contactors. Common causes include Faulty Hybrid/EV Battery Pre-Charge Resistor, Faulty Starter/Generator Control Module, Starter/Generator Control Module harness is open or shorted. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means: P0C78 GMC indicates Hybrid/EV Battery System Precharge Time Too Long.
Common causes: Common causes include Faulty Hybrid/EV Battery Pre-Charge Resistor, Faulty Starter/Generator Control Module, Starter/Generator Control Module harness is open or shorted.
Severity: High - diagnose this code as soon as possible.
Can I drive?: Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

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Code Popularity 635

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on Nov 21, 2019

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P0C78 GMC Description

The hybrid battery system voltage is controlled by two high voltage contactors. The high voltage contactors allow the high voltage DC batteries to be connected to the vehicle or safely contain the high voltage DC within the Hybrid/EV Battery Pack assembly. Of the two contactors, one is a pre-charge contactor and the other is the primary contactor. The two contactors are closed in a specific sequence by the Starter/Generator Control Module. The pre-charge contactor is closed first. This causes high voltage to flow through the pre-charge resistor, allowing system voltage to build slowly. Once the system voltage has raised and stabilized, the primary contactor is closed. Both contactors are controlled by the Starter/Generator Control Module. The Starter/Generator Control Module supplies B+ to each contactor at all times. When the contactors are to be closed, the Starter/Generator Control Module will provide a ground to the contactor through a low side driver.

OBDII Code P0C78 GMC - Hybrid/EV Battery System Precharge Time Too Long - AutoCodes.com — P0C78 GMC Code - Hybrid/EV Battery System Precharge Time Too Long

What does this mean?

What are the Possible Causes of the DTC P0C78 GMC?

Faulty Hybrid/EV Battery Pre-Charge Resistor
Faulty Starter/Generator Control Module
Starter/Generator Control Module harness is open or shorted
Starter/Generator Control Module circuit poor electrical connection

How to Fix the DTC P0C78 GMC?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0C78 GMC code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

Need more information about the P0C78 GMC code?

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About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about P0C78 GMC Code

1. What are the common symptoms of OBDII code P0C78 in a GMC vehicle?

- Common symptoms include the check engine light illuminating, reduced hybrid/EV system performance, and potential difficulty starting the vehicle.

2. What causes the OBDII code P0C78 "Hybrid/EV Battery System Precharge Time Too Long" in a GMC vehicle?

- The code is typically triggered by issues with the hybrid/EV battery system precharge circuit, such as a faulty precharge relay, wiring issues, or a malfunctioning battery pack.

3. How can I diagnose the OBDII code P0C78 in my GMC vehicle?

- Diagnosing this code usually involves using an OBDII scanner to retrieve the specific fault code, inspecting the hybrid/EV battery system components, and testing the precharge circuit for proper functionality.

4. What are the repair options for fixing OBDII code P0C78 in a GMC vehicle?

- Repair options may include replacing a faulty precharge relay, repairing damaged wiring, or addressing any issues with the hybrid/EV battery pack. It's recommended to consult a professional mechanic for an accurate diagnosis and repair.

5. Can I continue driving my GMC vehicle with OBDII code P0C78 present?

- It's not advisable to continue driving the vehicle with this code active, as it can lead to further damage to the hybrid/EV system components and potentially affect the vehicle's performance and safety.

6. How much does it typically cost to repair OBDII code P0C78 in a GMC vehicle?

- The repair costs can vary depending on the exact cause of the code and the needed repairs. It's recommended to obtain a diagnosis from a qualified mechanic to get an accurate estimate.

7. Are there any preventive maintenance steps to avoid OBDII code P0C78 in a GMC vehicle?

- Regularly inspecting and maintaining the hybrid/EV battery system components, including the precharge circuit, can help prevent issues that may trigger this code. Following the manufacturer's recommended maintenance schedule is also important.

8. Can I reset the OBDII code P0C78 in my GMC vehicle using an OBDII scanner?

- While resetting the code may temporarily turn off the check engine light, it's essential to address the underlying issue causing the code to prevent it from reoccurring. Simply resetting the code without proper diagnosis and repair is not a permanent solution.

9. Is OBDII code P0C78 specific to GMC vehicles, or can it occur in other makes and models?

- This particular OBDII code is specific to GMC vehicles, particularly those with hybrid or electric powertrains. However, similar issues related to the hybrid/EV battery system precharge circuit can occur in other makes and models as well.

10. How long does it typically take to repair OBDII code P0C78 in a GMC vehicle?

- The repair time can vary depending on the complexity of the issue and the availability of parts. Some repairs may be completed in a few hours, while more extensive repairs could take longer. It's best to consult with a mechanic for a more accurate time estimate.