Diagnostics basics
Can I diagnose my car myself?
Yes, up to a point: with an OBD reader you can read the trouble codes, the data from when the fault happened and live data, and from that tell which system is failing and how urgent it is. What you usually cannot tell is which exact part is bad without workshop tests. Use it to arrive informed, not to replace parts blindly.
Reviewed by Daniel Morales, founder of Reprorace SL, on
What can I do with a reader?
Read and note the trouble codes, with their status (pending or confirmed) and the freeze frame from when they were stored. Look up each code in a glossary to understand which system it affects.
Look at simple live data, such as engine temperature or battery voltage, and check the basics: the fuel cap, fluid levels with the engine cold, visibly loose connectors or a loose hose.
Why doesn't a code say which part to replace?
The code says which test failed, not what made it fail. A P0171 (system too lean) can come from a vacuum leak, a dirty airflow sensor or low fuel pressure.
So replacing the part the code names, and nothing else, often ends up costly. A workshop confirms the cause with measurements, tests and the manufacturer's service information.
When is it better not to touch anything?
If the check engine light flashes, the red oil, temperature or brake lights come on, or there is smoke or a burning smell, stop and get help: this is not the time to diagnose.
Do not clear airbag, brake or steering faults to get rid of a warning, and do not do coding or programming unless you know what you are doing: that is where you can leave the car worse off.
General guidance only: every manufacturer and model has its own details. Always follow your vehicle's manual and, if in doubt, ask a workshop.
Related
Related trouble codes
- P0420Catalyst system (bank 1): efficiency below threshold
- P0171Mixture too lean (bank 1)
- P0300Random or multiple cylinder misfire detected
Related symptoms
- Engine warning light on and steady: what it means and what to do
- Flashing engine warning light: what it means and what to do
Learn more
See what your car is saying
With the ECO-LITE you see the car's codes and data in your account and, if you need it, your workshop reviews them remotely and tells you whether the car needs to come in.
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Frequently asked questions
Do I need to know mechanics to read trouble codes?
No. Reading the code and understanding which system it affects is within anyone's reach; the repair is another matter.
Can I clear the codes myself?
You can, but write them down first. Clearing does not repair anything: if the cause remains, the light comes back. You also lose the fault data and the inspection monitors.
Will what I read help at the workshop?
Yes: arriving with the codes and the freeze frame saves diagnostic time.