Is it safe to drive with this code?

Driving may be possible for short distances, but the transmission may shift roughly or unpredictably, and continued driving could potentially cause further damage to transmission components. Limiting driving until diagnosed is advisable—see our disclaimer for guidance on seeking professional assessment.

The code itself won't directly cause MOT failure, but what matters is whether the malfunction indicator lamp is illuminated at the time of test. If the MIL is on, the vehicle may fail the emissions portion of the test—see our disclaimer for MOT-specific guidance.

Roughly how much does it cost to fix?

Repair costs typically fall in the low to mid three-figure range at an independent garage, depending on whether it's a simple wiring fix or requires solenoid replacement. Costs vary significantly based on whether diagnostics reveal just an electrical fault (lower end) or necessitate solenoid and fluid replacement (higher end). Main dealer rates may push costs toward the high three-figure range.

Can low transmission fluid cause this code?

While low or contaminated transmission fluid can affect solenoid performance, P078D specifically indicates an electrical circuit voltage issue rather than a hydraulic problem. However, checking fluid condition is often part of proper diagnostic procedure, as degraded fluid can contribute to solenoid electrical faults over time.

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← All fault codes | Gearbox

P078D

Powertrain

Shift Timing Solenoid B High

The engine control unit has detected that the shift timing solenoid B circuit is reading higher voltage than expected, which may indicate an electrical fault or solenoid issue in the transmission control system.

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ⓘ Information only. This page provides general educational information about fault code P078D. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.

Recommended next steps

Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.

What does P078D mean?

P078D is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Shift Timing Solenoid B High.

This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.

About Gearbox codes

Gearbox (transmission) codes report faults from the transmission control module: solenoid issues, fluid pressure problems, slipping clutches on dual-clutch boxes, and torque converter faults. Many trigger limp mode that locks the gearbox into a single forward gear.

P078D is one of 643 codes in this category. Browse all Gearbox codes →

What we know about P078D specifically

We record the SAE J2012 standardised definition and the system this code belongs to, but we have not yet published detailed driver-reported symptoms, common causes, or step-by-step diagnostic guidance for P078D.

Rather than invent that information by generating generic content from a template, we leave it out. For specific guidance, the most reliable sources are:

•your vehicle's own service manual or manufacturer-specific technical bulletins
•a qualified mechanic with a manufacturer-level diagnostic tool
•a marque specialist familiar with your make and model

Codes nearby

Codes adjacent to P078D in the P-code series. Many fault codes appear together with their neighbours because they relate to the same circuit or component.

P078A Shift Timing Solenoid B Malfunction

P078B Shift Timing Solenoid B Range/Performance

P078C Shift Timing Solenoid B Low

P078E Shift Timing Solenoid B Intermittent

P0790 Normal/Performance Switch Circuit Malfunction

P0791 Intermediate Shaft Speed Sensor Circuit Malfunction

Other Gearbox codes

Other fault codes in the same system as P078D. The ones with detailed guides have plain-English explanations, symptoms, causes, and diagnostic steps.

P0700

Transmission Control System Malfunction Detailed guide

P0701

Transmission Control System Range/Performance

P0702

Transmission Control System Electrical

P0703

Torque Converter/Brake Switch B Circuit

P0704

Clutch Switch Input Circuit Malfunction

P0705

Transmission Range Sensor Circuit Malfunction (PRNDL Input)

Spotted an issue or have something to add? Mechanics, technicians, and drivers who have first-hand experience with P078D can submit a correction or expansion. We review every submission before publishing, mechanic submissions are prioritised.

Information only, not professional advice

The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →

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