AutoCodes – Generic – P078C

P078C Code - Shift Timing Solenoid 'B' Low

Quick Answer

The Transmission Control Module (TCM) monitors the Shift Timing Solenoid 'B' circuit. Common causes include Faulty Shift Timing Solenoid 'B', Shift Timing Solenoid 'B' harness is open or shorted, Shift Timing Solenoid 'B' 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: P078C indicates Shift Timing Solenoid 'B' Low.
Common causes: Common causes include Faulty Shift Timing Solenoid 'B', Shift Timing Solenoid 'B' harness is open or shorted, Shift Timing Solenoid 'B' 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 1,637

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, 2019

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P078C Description

The Transmission Control Module (TCM) monitors the Shift Timing Solenoid 'B' circuit. The TCM sets the OBDII code when the Shift Timing Solenoid 'B' is out of factory specifications.

OBDII Code P078C - Shift Timing Solenoid 'B' Low - AutoCodes.com — P078C Code - Shift Timing Solenoid 'B' Low

What does this mean?

What are the Possible Causes of the DTC P078C?

Faulty Shift Timing Solenoid 'B'
Shift Timing Solenoid 'B' harness is open or shorted
Shift Timing Solenoid 'B' circuit poor electrical connection

How to Fix the DTC P078C?

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 P078C 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 P078C Code

1. What does the OBDII code P078C mean?

P078C indicates that the transmission control module (TCM) has detected a low electrical signal from Shift Timing Solenoid 'B', which helps regulate gear shifting in the transmission.

2. What are the common symptoms of a P078C code?

Symptoms may include harsh or delayed shifting, transmission slipping, poor acceleration, reduced fuel economy, and the illumination of the Check Engine Light.

3. What causes the P078C code to appear?

Common causes include a faulty Shift Timing Solenoid 'B', damaged wiring or connectors, low or contaminated transmission fluid, or an issue with the TCM.

4. Can I drive with a P078C code?

While the vehicle may still be drivable, continuing to drive with this code can cause further transmission damage. It’s best to address the problem as soon as possible.

5. How do I diagnose the P078C code?

Diagnosis involves checking the transmission fluid level and condition, inspecting wiring and connectors for damage, testing the solenoid for proper function, and using a scan tool to monitor TCM signals.

6. How can I fix the P078C code?

Repairs may include replacing Shift Timing Solenoid 'B', repairing or replacing damaged wiring or connectors, flushing and refilling the transmission fluid, or reprogramming or replacing the TCM.

7. How much does it cost to repair a P078C code?

Repair costs vary but typically range from $200 to $500 for solenoid replacement, depending on labor rates and vehicle type. Additional costs may apply if further repairs are needed.

8. Can low transmission fluid cause the P078C code?

Yes, low or contaminated transmission fluid can cause the solenoid to malfunction, leading to the P078C code.

9. How do I prevent the P078C code from recurring?

Regular transmission maintenance, including fluid changes and inspections for wiring issues, can help prevent the code from recurring.

10. Does the P078C code always require solenoid replacement?

Not always. The issue could be due to wiring problems, fluid issues, or a fault in the TCM, so proper diagnosis is essential before replacing the solenoid.