- 14+ yearshands-on experience
- 24/7emergency callouts
- Insuredpublic liability cover
- Upfront priceagreed before work starts
What a diagnostic check actually involves
Plugging a code reader into your car's diagnostic port is the start of a diagnosis, not the end of it. The car's control units, for the engine, gearbox, ABS, airbags and body electrics, store fault codes when something is out of range. But a fault code tells you which system or circuit has a problem, not which part has failed.
For example, a code saying the engine is running lean could be caused by an air leak, a faulty sensor, a fuel delivery problem or a wiring fault. Replacing the sensor named in the code is a common and expensive guess. A proper diagnosis combines:
- Reading stored and pending fault codes from every control unit, not just the engine
- Live data, watching sensor readings while the engine runs to see what's actually happening
- Freeze-frame data, the conditions recorded at the moment the fault was logged
- Physical and electrical testing of the suspect components, wiring and connections
The goal is to find the cause once, so you only pay for the part that's actually faulty.
Common warning lights and what to do
As a general rule, red warning lights mean stop as soon as it's safe, and amber lights mean get it checked soon. Your handbook is the final word for your car.
| Warning light | What it usually means | What to do |
|---|---|---|
| Engine management (amber, steady) | An engine or emissions fault has been logged | Get it diagnosed soon. Driving gently is usually OK. |
| Engine management (flashing) | Often a misfire, which can damage the catalytic converter | Reduce speed and stop when safe |
| Oil pressure (red) | Low oil pressure | Stop the engine as soon as it's safe |
| Temperature (red) | Engine overheating | Stop and switch off. Don't open a hot coolant cap. |
| Battery (red) | Charging system fault | Limited driving time. See our battery light guide. |
| Brake (red) | Low brake fluid or a brake system fault | Don't drive until checked |
| ABS (amber) | The anti-lock system is disabled | Normal brakes work, ABS may not. Get it checked. |
| Airbag (amber or red) | An airbag system fault | Airbags may not deploy in a crash. Get it checked. |
| DPF (amber, diesel) | Particulate filter is filling up | See our DPF cleaning page |
| Glow plug (diesel, flashing) | Often an engine fault on many diesels | Get it diagnosed soon |
Electrical faults
Electrical problems are often intermittent, which makes them hard to pin down at a busy garage where the car is looked at for ten minutes. Typical faults we trace include:
- Batteries that go flat overnight because something is drawing power
- Faulty sensors and the wiring to them
- Central locking, electric window and lighting faults
- Corroded connectors and poor earth connections
- Faults that only appear when the engine is warm or after rain
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Warning lights and your MOT
An engine management light that stays on is an MOT failure, and so are ABS and airbag warning lights that indicate a fault. Clearing the code with a cheap reader doesn't fix anything: the light comes back, and the car's readiness monitors can show that codes were recently cleared. It's always cheaper to find and fix the cause.
What we'll be upfront about
Our diagnostic equipment covers the vast majority of makes and models on UK roads. Many faults can be fixed on the same visit once they're found, such as a sensor, connector or component swap. A small number of jobs, like some manufacturer-specific software updates or programming, can only be done with dealer systems. If your fault falls into that category, we'll tell you as soon as we know, rather than charge you to find out.
What it costs
Tell us your registration and what the car is doing, including any warning lights, and we'll give you a price for the diagnosis before we arrive. Once we've found the cause, you get a clear explanation and a price for the repair, and you decide whether to go ahead.
Want more detail? Read what a mobile car diagnostic check includes.
Other services
Where we work
We're based in Small Heath, Birmingham, and come to you across the West Midlands, including these areas:
Frequently asked questions
What does a diagnostic check actually find?
It reads stored fault codes from the engine, gearbox, ABS, airbag and other control units, and looks at live sensor data while the engine runs. Combined with physical testing, that pinpoints the actual cause rather than guessing from a code.
Can I just clear the warning light myself?
You can clear a code, but the fault is still there, so the light will come back. A lit engine management light is also an MOT failure, so it's worth finding the cause.
Is it safe to drive with the engine management light on?
A steady amber light usually means you can drive gently until it's checked. A flashing light often means a misfire, so reduce speed and stop when it's safe. Red warning lights mean stop.
Will you fix the fault on the same visit?
Often, yes. Many faults are a sensor, connector or component that can be replaced on the spot. If parts need ordering, you'll get a clear explanation and a price first.
Do you cover hybrid vehicles?
Our equipment covers the vast majority of makes and models, including many hybrids. Send your registration and we'll confirm before booking.