U0100 OBD-II code — what it means and what to check
ℹ Guidance only — not a substitute for inspectionEnter the trouble codes from your scanner to see what each one means, how urgent it is, and which checks to do first.
Your codes, interpreted
What this means
⚠ Have this looked at now. At least one code you entered should not be left until the next service.
What to doArrange a workshop inspection now, and keep journeys short and local until then.
Your codes
- U0100 — Vehicle network (service now). A control module has lost communication with the engine computer over the vehicle's data network. This is a fault in the network or the power feeding it, not usually in any one module.
Checks to do first, in order
- Check the battery and its terminals first — low voltage and corroded terminals are the most common cause by a wide margin.
- Read all stored codes: companion codes usually name which module dropped off.
- Inspect the wiring loom for chafing or pinched wires, particularly anywhere recent work was done.
- Have the network resistance measured across pins 6 and 14 of the diagnostic socket — about 60 ohms is normal, and a very different reading points at the wiring or a terminating resistor.
- Suspect a module itself only once power, earth and wiring are ruled out.
Codes this tool cannot interpret
How this result was reached
- Interpretations cover standardised codes only, and describe what a code means rather than what is wrong with your specific vehicle.
- A stored code identifies the circuit or system reporting a fault. It does not identify the failed part — a sensor commonly reports a problem it did not cause.
- Reviewed by Project Owner on 2026-08-26.
- This tool covers a reviewed subset of standardised codes. A code it does not recognise is reported as undocumented rather than guessed at.