Is it safe to drive with this code?

Driving may be possible in the short term, but many vehicles will enter limp mode to protect the gearbox, which restricts performance and can make motorway driving unsafe. Prolonged operation with incompatible software may cause additional stress on transmission components. For full context on liability, see our site disclaimer.

It may affect your MOT outcome if the malfunction indicator lamp is illuminated at the time of the test, as an active dashboard warning can constitute a Major defect under MOT regulations. What matters is the lamp's status during inspection—refer to our disclaimer for guidance.

Roughly how much does it cost to fix?

Costs vary widely depending on the repair required. A straightforward software reflash at an independent garage often falls into the low three-figure range, while main-dealer diagnostics and programming can reach the mid three-figure band. If a module requires replacement and reprogramming, expect high three-figure to four-figure sums, as specialist equipment and VIN coding are usually needed. Labour rates differ significantly between independent workshops and franchised dealers.

Can I just clear the code and keep driving?

Clearing the fault code without addressing the underlying software mismatch will typically cause U0304 to return immediately or after a short drive cycle. The modules will continue to detect the incompatibility each time they attempt to communicate, so a proper reflash or module replacement is usually necessary for a lasting repair.

Professional mechanic working in workshop

← All fault codes | Gearbox

U0304

Network

Software Incompatibility With Gear Shift Control Module "A"

The engine control module and gear-shift control module are running mismatched software versions and cannot communicate properly.

garage.co.uk

Need a garage?

Compare quotes from verified UK garages near you.

→

car.co.uk

Sell your car

We specialise in problem cars: warning lights, faults, high mileage. Fair instant offer.

→

trader.co.uk

List your car

Free private listing. Reach thousands of UK buyers, no fees.

→

ⓘ Information only. This page provides general educational information about fault code U0304. 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 U0304 mean?

U0304 is a Network (CAN bus, module communications) fault code. It indicates: Software Incompatibility With Gear Shift Control Module "A".

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.

U0304 is one of 643 codes in this category. Browse all Gearbox codes →

What we know about U0304 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 U0304.

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 U0304 in the U-code series. Many fault codes appear together with their neighbours because they relate to the same circuit or component.

U0300 Internal Control Module Software Incompatibility

U0302 Software Incompatibility With Transmission Control Module

U0303 Software Incompatibility With Transfer Case Control Module

U0305 Software Incompatibility With Cruise Control Module

U0306 Software Incompatibility With Fuel Injector Control Module

U0307 Software Incompatibility With Glow Plug Control Module

Other Gearbox codes

Other fault codes in the same system as U0304. 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 U0304 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 →

✎

Help us improve the U0304 page

Spotted an error, missing detail, or have first-hand experience to add? Tell us, we review every submission.