AutoCodes – GMC – C0166 GMC

C0166 GMC Code - TCS Priming Line Valve Circuit Malfunction

Quick Answer

The Master Cylinder Isolation Valve, or TCS Prime Valve Solenoid circuits are supplied with battery power when the ignition is in the RUN position. Common causes include Faulty TCS Prime Valve Solenoid, TCS Prime Valve Solenoid harness is open or shorted, TCS Prime Valve Solenoid 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: C0166 GMC indicates TCS Priming Line Valve Circuit Malfunction.
Common causes: Common causes include Faulty TCS Prime Valve Solenoid, TCS Prime Valve Solenoid harness is open or shorted, TCS Prime Valve Solenoid 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.

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Code Popularity 954

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 May 08, 2020

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code C0166 GMC Description

The Master Cylinder Isolation Valve, or TCS Prime Valve Solenoid circuits are supplied with battery power when the ignition is in the RUN position. The Electronic Brake Control Module (EBCM) controls the valve functions by grounding the circuit when necessary.

OBDII Code C0166 GMC - TCS Priming Line Valve Circuit Malfunction - AutoCodes.com — C0166 GMC Code - TCS Priming Line Valve Circuit Malfunction

What does this mean?

What are the Possible Causes of the DTC C0166 GMC?

Faulty TCS Prime Valve Solenoid
TCS Prime Valve Solenoid harness is open or shorted
TCS Prime Valve Solenoid circuit poor electrical connection

How to Fix the DTC C0166 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 C0166 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.

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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 C0166 GMC Code

1. What does the OBDII code C0166 mean on a GMC vehicle?

C0166 indicates a malfunction in the Traction Control System (TCS) priming line valve circuit, which is part of the vehicle's stability and traction control system.

2. What are the common symptoms of the C0166 code on a GMC?

Symptoms may include the ABS or TCS warning lights illuminating, reduced traction or stability control performance, and difficulty maintaining vehicle stability during slippery conditions.

3. What causes the C0166 code to appear?

Common causes include a faulty TCS priming line valve, damaged wiring or connectors in the valve circuit, or a malfunctioning ABS control module.

4. Can I still drive my GMC with the C0166 code?

You can drive the vehicle, but it is not recommended as the ABS and traction control systems may not function properly, increasing the risk of skidding or loss of control in certain situations.

5. How do I diagnose the cause of the C0166 code?

Start by checking the wiring and connectors for damage or corrosion, then test the TCS priming line valve for proper operation. If no issues are found, inspect the ABS control module.

6. How do I fix the C0166 code on my GMC?

Repairs may involve replacing the TCS priming line valve, repairing or replacing damaged wiring or connectors, or replacing the ABS control module if it's determined to be faulty.

7. How much does it cost to repair the C0166 code?

Repair costs vary depending on the exact issue, but replacing a TCS priming line valve can cost $150-$300, while ABS control module replacement may range from $500-$1,200.

8. Can a bad wheel speed sensor cause the C0166 code?

A bad wheel speed sensor is unlikely to directly cause this code, as it specifically relates to the TCS priming line valve circuit. However, other related issues may coexist.

9. How can I prevent the C0166 code from returning?

Regularly inspect and maintain the ABS and traction control system components, including wiring and connectors. Address any warning lights or performance issues promptly.

10. Will clearing the C0166 code with a scan tool fix the problem?

Clearing the code may turn off the warning light temporarily, but the issue will likely return unless the underlying problem is properly diagnosed and repaired.