Mobile Car Diagnostics

A warning light tells you the car has recorded a fault. It does not tell you what is broken. Mobile car diagnostics means we come to the car with the equipment to read what the engine management system has stored, interpret it properly, and work out what is actually causing the problem.

Reading a fault code takes seconds. Understanding it takes longer, and that is the part that matters. A code will usually point at a circuit or a system rather than a component, and several different faults can produce the same code.

A proper diagnostic runs roughly like this:

• Read the stored and pending fault codes across the car’s modules
• Look at live sensor data while the engine is running, rather than codes alone
• Check the wiring, connectors and earths in the circuit the code points to
• Test the suspected component before condemning it
• Clear the codes and confirm the fault does not return

That last step matters. A fault that has been cleared but not fixed will come back, usually at a worse moment.

A common example is an oxygen sensor code. It can mean the sensor has failed, but it can equally mean there is an exhaust leak upstream, a wiring fault, or a fuelling problem the sensor is correctly reporting. Replacing the sensor on the strength of the code alone fixes the fault perhaps half the time, and you have still paid for the part.

This is the main reason we test before replacing. It is slower on the day and cheaper overall.

• Engine management and check engine lights
• ABS and traction control warnings
• Airbag and SRS lights
• Intermittent non-starting and flat batteries that keep recurring
• Misfires, rough running and poor starting
• Electrical faults with no warning light at all
• Charging system and alternator problems

Electrical faults with no code stored are the ones garages tend to struggle with, because there is nothing to read. Those come down to testing the circuit properly.

Intermittent faults are often the hardest to reproduce, and a car that has been driven across town to a garage has frequently stopped doing the thing you wanted looked at. Testing where the car normally sits, in the condition it normally sits in, gives a better chance of catching it. Cold-start faults are the clearest case of this.

We carry out diagnostics across South London and Surrey, including Croydon, Epsom and Kingston.

Related work: auto electrical repairs and mobile car battery replacement, which is where a surprising number of electrical faults end up. The full list of services covers the rest.

Tell us the make, model and registration, which lights are on, and what the car is doing that made you call. If the fault only happens under particular conditions, say so, because that shapes how we test it.