Battery and electrics
What happens if I disconnect the battery: are the codes erased?
On many cars, yes: removing the battery erases the engine ECU's codes and turns the light off, but also the freeze frame data, the readiness monitors and some learned values. On others the codes live in permanent memory, and on all of them the light comes back on if the fault is still there.
Reviewed by Daniel Morales, founder of Reprorace SL, on
What else is lost when the battery is disconnected?
Depending on the car, the radio, the clock, the one-touch windows, the sunroof and the idle and transmission adaptations. Some need a procedure to get them back.
Cars with start-stop and a battery sensor may need the new battery to be registered with a diagnostic tool after replacement.
Is it a bad idea to do it to turn the light off?
Yes. It fixes nothing, it erases the clues to the fault and the incomplete monitors give the clearing away at an inspection or a sale.
Disconnecting with the ignition on or the engine running can also damage the electronics; always follow the owner's manual.
How do I replace the battery without losing anything?
Read and write down the codes first. Many shops use a memory saver connected to the OBD port or the terminals so the car never loses power.
Then let the car relearn over a few days of driving and check that no new codes appear.
General guidance only: every manufacturer and model has its own details. Always follow your vehicle's manual and, if in doubt, ask a workshop.
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Learn more
See what your car is saying
The ECO-LITE keeps the codes read before you disconnect the battery in your account, and afterwards shows you how the monitors complete.
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Frequently asked questions
How long must it stay disconnected to clear codes?
It depends on the car; do not do it to clear faults: write them down and clear them with a scanner.
Are ABS and airbag codes erased?
Usually not: those modules keep their codes in permanent memory.
Can the car run oddly afterwards?
For a while, yes: rough idle or harsh shifts until it relearns. If it persists, have it checked.