C1123 — 5 documented meanings by make

C1123 does not mean the same thing on every car — manufacturers reuse the number for different faults. 6 makes document it: Ford, Mazda, Mercedes-Benz, Opel / Vauxhall, Subaru, Suzuki. Find your make below.

C1123 on Ford, Mazda

On Ford, Mazda vehicles C1123 is documented as: Vehicle speed sensor failure. C1123 is stored when the ECU sees malfunction on vehicle speed signal. That describes how the circuit is behaving, not which part has failed — the wiring, the connector and the component itself can all produce it, which is why the checks below start with the cheapest.

Usually one of: Wiring or connector fault in the circuit; Component failed electrically; Supply or ground problem feeding the circuit; Controlling module fault, though this is the least common of the four.

Check first, cheapest first:

1. Read all stored codes — a general fault code is often the symptom of a more specific one
2. Inspect the connector and wiring for the named component
3. Check supply and ground at the component
4. Measure the component against specification
5. Replace the component once wiring and supply are ruled out

Related Ford, Mazda codes:

C1123 on Mercedes-Benz

On Mercedes-Benz vehicles C1123 is documented as: AIRMATIC: fault in component B24/6 (accelerator sensor). C1123 is stored when the ECU sees malfunction on the circuit named in the code. That describes how the circuit is behaving, not which part has failed — the wiring, the connector and the component itself can all produce it, which is why the checks below start with the cheapest.

Usually one of: Wiring or connector fault in the circuit; Component failed electrically; Supply or ground problem feeding the circuit; Controlling module fault, though this is the least common of the four.

Check first, cheapest first:

1. Read all stored codes — a general fault code is often the symptom of a more specific one
2. Inspect the connector and wiring for the named component
3. Check supply and ground at the component
4. Measure the component against specification
5. Replace the component once wiring and supply are ruled out

Related Mercedes-Benz codes:

C1123 on Opel / Vauxhall

On Opel / Vauxhall vehicles C1123 is documented as: No vehicle speed signal. C1123 points at vehicle speed signal. The standard definition names the system involved; which part inside it has actually failed is what the checks below establish, cheapest first.

Related Opel / Vauxhall codes:

C1123 on Subaru

On Subaru vehicles C1123 is documented as: Vehicle speed sensor circuit. C1123 points at vehicle speed signal. The standard definition names the system involved; which part inside it has actually failed is what the checks below establish, cheapest first.

Related Subaru codes:

C1123 on Suzuki

On Suzuki vehicles C1123 is documented as: Vehicle speed sensor circuit signal no input, 30 seconds or more. C1123 points at vehicle speed signal. The standard definition names the system involved; which part inside it has actually failed is what the checks below establish, cheapest first.

Related Suzuki codes:

Which one is yours

A generic OBD reader gives you the number, not which of these meanings your manufacturer assigned to it. To get to the specific one:

1. Use a brand-specific scanner — VCDS for VAG, INPA or ISTA for BMW, XENTRY for Mercedes, Forscan for Ford. It shows the manufacturer's own text rather than the generic one.
2. Read all stored codes together — the neighbouring ones usually point at which system is involved and narrow the list.
3. Check freeze-frame data: the RPM, temperature and load at the moment it triggered indicate which system was active.
4. If you have no brand scanner, tell me the make and model below and I will tell you which of these applies to your car.

Code family

C1xxx is suspension, steering, active systems.

Severity

Suspension or steering — on active systems (ESP, air suspension) the code usually comes from a sensor, not the part itself.

That is what holds for C1123 in general. From here it depends on your engine — tell me which car it is and what it does, and I will give you the steps for it: real procedures, torque figures and diagrams instead of general advice.