How to reset Check Engine via OBD-II
LLCAR Editorial · published
Read the codes and save the available freeze frame. After fixing the cause, erase the codes with a compatible OBD-II scanner and read them again immediately. If the fault remains or returns, the control unit may record the code again and turn the light back on.
When the reset should wait
If the light is on steadily, save the diagnostic data and start checking. If you plan an inspection at a service shop, leave the codes in memory until the inspection. The technician may ask you to clear them as part of diagnostics after saving the readings. What a steady or flashing Check Engine means.
Four steps via OBD-II
- 1. ReadGet the control unit's response
- 2. SaveRecord the codes and freeze frame
- 3. ClearAfter fixing the cause
- 4. Re-readCheck the fresh response
- Read the engine codes with the car stationary. Connect a compatible scanner. See the car's and scanner's instructions for the ignition position and connection conditions. Make sure the device received a response from the control unit. How to connect ELM327 to your phone.
- Save the full list of codes and their statuses. Take a screenshot. If a freeze frame is available, save it too. It may contain RPM, temperature, load and other parameters at the moment the fault was recorded. Note the mileage and the conditions when the light came on. How to read codes from your phone.
- Clear the codes after fixing the cause. On a compatible scanner the command may be called "Erase codes" or Clear DTCs. Clearing may remove stored codes, the freeze frame and self-test results.
- Re-read the codes and check the fresh response. Make sure the scanner confirmed the clear and received a new response from the control unit. If the connection dropped, restore it and read the codes again first. Then watch the light and the codes under the conditions specified in the car's manual.
Why Check Engine came back
The control unit runs its self-tests again. Some run immediately; others need a certain temperature, load or driving mode. If the problem shows up under acceleration, the light may come on specifically during acceleration. Save the new code and freeze frame and compare the conditions with the earlier record. This makes it easier for the technician to reproduce the symptom.
What scanner statuses mean
| Mark | What it means |
|---|---|
| Pending Pending code | The control unit noticed a deviation. Additional conditions may be required for confirmation. Such a code can be visible with the light off. |
| Permanent Permanent code | On cars that support this mode, the clear command does not remove it. The control unit clears the code itself after the required test. |
| Readiness Readiness | Shows which self-tests have completed. After clearing, some tests may again wait for the right conditions, even if the light has gone off. |
Can you do it without a scanner
After the cause is fixed, the light may go off on its own once the car completes the required test. The stored code sometimes remains accessible. Disconnecting the battery terminal to force a reset is not a good idea. It can reset the readiness of self-tests, while a permanent code will persist. Use a compatible scanner for reading and controlled clearing. How to choose an ELM327 adapter.
How LLCAR tells a recurring code apart
In the Android build of LLCAR AI0.19, three fresh complete readings of the same mode without the code allow the next appearance to be treated as a new episode. Communication failures or repeats of an old response do not count toward these readings. This is a rule for displaying a recurring event in the app. The outcome of a repair is judged from the car's fresh data and the test conditions.