AutoCodes – Buick – P0C78 Buick

P0C78 Buick 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 Buick 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 1,057

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

What does this mean?

What are the Possible Causes of the DTC P0C78 Buick?

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 Buick?

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 Buick 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 Buick 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 Buick Code

1. What are the common symptoms of OBDII code P0C78 in a Buick hybrid/EV vehicle?

- Common symptoms include reduced power, poor fuel economy, and the vehicle going into a reduced propulsion mode.

2. What does the OBDII code P0C78 in a Buick hybrid/EV indicate?

- The code indicates that the hybrid/EV battery system precharge time is too long, leading to potential performance issues.

3. What are the possible causes of OBDII code P0C78 in a Buick hybrid/EV?

- Possible causes include a faulty precharge relay, issues with the high voltage interlock circuit, or problems with the battery management system.

4. How can I diagnose the OBDII code P0C78 in a Buick hybrid/EV?

- A thorough diagnostic scan using an OBDII scanner capable of reading hybrid/EV codes can help pinpoint the exact cause of the issue.

5. What are some repair tips for fixing OBDII code P0C78 in a Buick hybrid/EV?

- Repair tips may include checking and replacing the precharge relay, inspecting the high voltage interlock circuit for faults, and ensuring proper functioning of the battery management system.

6. Can driving with OBDII code P0C78 in a Buick hybrid/EV cause further damage?

- Driving with this code may lead to reduced performance and fuel efficiency, so it's advisable to address the issue promptly to prevent potential damage to the hybrid/EV system.

7. How much does it typically cost to repair OBDII code P0C78 in a Buick hybrid/EV?

- Repair costs can vary depending on the exact cause of the issue, but they may range from a few hundred to over a thousand dollars, including parts and labor.

8. Is it safe to continue driving my Buick hybrid/EV with OBDII code P0C78 present?

- It is not recommended to drive the vehicle with this code present, as it may lead to further performance issues and potentially cause damage to the hybrid/EV system.

9. Can a DIY enthusiast repair OBDII code P0C78 in a Buick hybrid/EV?

- While some basic diagnostics can be done by DIY enthusiasts, repairing this code often requires specialized knowledge and tools, so it's best to consult a professional technician.

10. How often does OBDII code P0C78 occur in Buick hybrid/EV vehicles?

- The occurrence of this code can vary, but it is not uncommon in older or higher mileage Buick hybrid/EV models experiencing issues with the battery system precharge time.