A fault code doesn’t yet mean the unit or sensor itself is faulty: often it’s the plug and connector leading to it.
Possible causes
- Power or ground of this control unit (fuse)
- CAN bus connector or wire
- The control unit itself
- Low battery voltage
What you can do yourself
- Check the battery and terminals: at low voltage control units lose communication.
- Check this control unit’s fuses.
Stop and don’t drive on if:
- The instrument panel went dark or many warning lights came on at once
- Power steering is gone or the brakes don’t work as usual
OOleg’s tip: check the connector
Often the cause is simple — there is no contact in the connector (plug). Look at the connector from the back: remove the rubber seal and you will see whether a wire is corroded or has come off completely. Corrosion shows up as green deposits. Ideally, gently pull each wire towards you one at a time: a sound wire stays in place, while a corroded one simply comes off — it needs to be repaired.
Unplug and inspect connectors with the ignition off.
OOleg’s tip: don’t pressure-wash the engine
Never wash the engine with a Kärcher (a pressure washer), steam or anything like that — there’s a special foam cleaner for that. Once the rubber seals in the connectors have dried out, moisture gets inside and the sensor connectors and the computer (ECU) connector rot.
OA case from Oleg’s practice
- Cadillac CTS Coupe 2011 Cranks but won’t start; code U0100 — lost communication with the engine control module. The cause was corroded wiring that disrupted power and communication with the ECU. We repaired that section and cleaned the contacts — it started, communication is back. How it went ↗
On Oleg’s website:Car wiring repair ↗
The explanation comes from the error code reference in the AvtoElektrik PRO app.