Lost Communication With Engine Control Module A
What it means
The control units in the car exchange data over an internal network, and this code means another unit, such as the transmission computer or instrument cluster, has stopped receiving messages from the engine computer. The cause can be as simple as a weak battery or as serious as damaged wiring or a failed engine computer.
Symptoms
- Car will not start or stalls suddenly.
- Several warning lights on at once.
- Gauges dead or moving erratically.
- Transmission in limp mode.
- Scan tool cannot communicate with the engine computer.
Possible causes
- Weak battery or loose terminals causing low voltage.
- Blown fuse or failed relay feeding the engine computer.
- Damaged ground connection for the engine computer.
- Damaged network wiring or corroded connector.
- Water entering the engine computer or its connector.
- Internal engine computer failure.
How to diagnose and fix
- Check the battery and terminals and confirm healthy voltage.
- Check the fuses and relay supplying the engine computer.
- Inspect and clean ground connection points.
- Inspect the engine computer connector for water or corrosion.
- Have an auto electrician test the network wiring and its resistance.
- Do not replace the engine computer until power, ground and wiring are confirmed good, as it usually needs programming.
Repair cost
Costs start with a battery or fuse and rise if network wiring must be repaired or the engine computer replaced and programmed.
Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Frequently asked questions
Is it safe to drive with this code?
If the car stalls or behaves unpredictably, do not drive it, because stalling on the road is dangerous. Have it towed or inspected where it is.
Can the battery really be the cause?
Yes. Low voltage is one of the most common causes of communication codes, so always check the battery and connections before any costly repair. Never unplug or reconnect computer connectors with the ignition on.
This guide is for information only and does not replace an inspection by a qualified technician. If the fault involves brakes, steering, engine temperature, electrics or refrigerant, do not attempt the repair yourself.
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