The amber engine-shaped warning light (also called the MIL or check engine light) means the engine control unit has detected a fault that may affect emissions or how the engine runs. Any OBD2 scanner can switch it off, but if you don't fix the cause, it will come back on. The key is to read the fault properly before you clear it.
Steady or flashing light
- Steady: a fault has been stored. You can keep driving with care until it is diagnosed, but don't leave it too long.
- Flashing: usually means a serious misfire that can damage the catalytic converter. Take it easy on the engine and get it checked as soon as possible. We explain it in P0300 code: misfire detected.
Safety: if the light is flashing, or you notice strong jerking, a burning smell or loss of power, stop the car somewhere safe. Carrying on like that can damage the catalytic converter and other components.
Step by step: reading and clearing the fault
- Find the OBD2 port, usually under the steering wheel, and plug in the tool's cable with the engine off.
- Turn the ignition on without starting. That is what iCarsoft recommends for reading and clearing codes: ignition on, engine off.
- Identify the vehicle by VIN or manually. For a quick emissions read you can use the generic OBD2/EOBD menu; to reach every system, use the make-specific diagnostics.
- Read the codes from the engine control unit. Note down each code (for example P0420 or P0171) and its description. Check the pending codes too: they are faults that have been detected but have not yet turned the light on.
- Save the freeze frame before clearing. It is the engine data at the moment the fault appeared: temperature, revs, load, speed. If you clear first, you lose it.
- Fix the cause. Look at the live data and check connectors, sensors and hoses. A code does not always point to the faulty part, but to the symptom the control unit picked up.
- Clear the codes using the erase faults option and confirm.
- Switch the ignition off, wait and switch it back on. Start the engine and check that the light goes out after the dash's initial bulb check.
- Do a mixed drive cycle (town and open road), then read the faults again along with the readiness monitor status (I/M Readiness).
How to read a fault code
OBD2 codes have one letter and four digits. The letter tells you the system: P for powertrain (engine and transmission), B for body, C for chassis and U for network communication between control units. If the first digit is 0, the code is generic and means the same on every make; if it is 1, it is manufacturer-specific and it is worth reading its description on the tool using make-specific diagnostics. The engine warning light mainly responds to P codes.
Why the light comes back on
If the fault is real, the control unit detects it again on the next cycle and turns the light back on. There are also physical faults that won't clear while they are still present; in its FAQs, iCarsoft points out that permanent hardware faults must be repaired before they can be cleared, and that some systems such as the airbag may need extra steps.
| What you see | What it usually means |
|---|---|
| The code clears and stays away | A one-off glitch, or already fixed |
| It clears and returns after a few miles | The cause is still there: it needs diagnosing |
| It won't clear | A fault present right now, or a hardware failure |
| Light off but pending codes stored | Fault detected once, not yet confirmed |
Before your roadworthiness test: clearing faults just before the inspection (NCT, MOT or your country's equivalent) resets the emissions monitors. Many test centres check whether they are complete and note it on the result. Clear the codes in good time and drive the car for several days before you go.
Which iCarsoft tools clear the engine warning light
Every iCarsoft diagnostic tool reads and clears engine codes. The difference is what else they can do:
- CR Pro: every system on 58 makes and all ten OBD2 test modes (read and clear codes, pending codes, I/M Readiness, live data, freeze frame, O2 sensor test, on-board monitors, EVAP system and vehicle information).
- CR Pro+: the same, plus bidirectional control to activate components and confirm the fault.
- CR Max: a 7" tablet with 50 service functions, comfortable for following live data.
- VAWS V2.0 and other single-brand tools: every system on one make or group. You will find them under single-brand diagnostic tools.
If you just want to know what is wrong with your car and switch the light off once it is fixed, any of them will do. If you plan to diagnose in depth, have a look at our CR Pro vs CR Pro+ comparison.
The most searched-for codes
If your scan shows P0420, read what the P0420 code means. If it is P0300 or a P030X, see our guide to misfire codes. And if the light on your dash is not the engine light but the service reminder, what you need is a service reset.
