AutoCodes – Generic – B0978

B0978 Code - Accessory Indicator Control Circuit

Quick Answer

The Ignition Mode Switch has 3 LEDs that indicate the vehicle power mode. Common causes include Faulty Ignition Mode Switch, Ignition Mode Switch harness is open or shorted, Ignition Mode Switch circuit poor electrical connection. 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: B0978 indicates Accessory Indicator Control Circuit.
Common causes: Common causes include Faulty Ignition Mode Switch, Ignition Mode Switch harness is open or shorted, Ignition Mode Switch circuit poor electrical connection.
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.

Save to My Repairs My Repairs

AI answers can be wrong. Verify repairs with testing. Open full chat

Code Popularity 1,136

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 Mar 11, 2021

Description
Possible Causes
How To Fix
Cost to Diagnose
Comments
Add Comment

💬 Need more help? Ask Coddy for instant answers — it's free!

Code B0978 Description

The Ignition Mode Switch has 3 LEDs that indicate the vehicle power mode. When the vehicle is in the Off mode, the Off LED may illuminate. Pressing the lower button of the ignition mode switch, the vehicle enters the accessory mode and ACC LED will illuminate. Keeping the lower button pressed for about 5-6 seconds, the vehicle enters run mode with the engine off and the START LED will illuminate. All these LEDs have the voltage supplied from the Body Control Module (BCM) through the ignition mode switch supply voltage circuit. The ground path for each LED is controlled by the BCM.

OBDII Code B0978 - Accessory Indicator Control Circuit - AutoCodes.com — B0978 Code - Accessory Indicator Control Circuit

What does this mean?

What are the Possible Causes of the DTC B0978?

Faulty Ignition Mode Switch
Ignition Mode Switch harness is open or shorted
Ignition Mode Switch circuit poor electrical connection
Faulty Body Control Module (BCM)

How to Fix the DTC B0978?

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 B0978 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 B0978 code?

Need more information on how to fix the B0978 code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the B0978 code diagnosed by a professional: Find a repair shop in your area

Information for Specific Makes

B0978 Buick — Accessory Indicator Control Circuit
B0978 Cadillac — Accessory Indicator Control Circuit
B0978 Chevrolet — Accessory Indicator Control Circuit
B0978 GMC — Accessory Indicator Control Circuit

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.