P1231 — 11 documented meanings by make

P1231 does not mean the same thing on every car — manufacturers reuse the number for different faults. 13 makes document it: Audi, Chevrolet (Daewoo), Chevrolet (USA), Citroen, Ford, Mazda, Mitsubishi, Opel / Vauxhall, Peugeot, Saab, SEAT, Skoda, Volkswagen. Find your make below.

P1231 on Audi, SEAT, Skoda, Volkswagen

On Audi, SEAT, Skoda, Volkswagen vehicles P1231 is documented as: Injector cylinder 7, N85, short circuit to ground. P1231 is stored when the ECU sees short to ground on fuel injector (cylinder 7). 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 insulation chafed through where the loom passes a bracket or edge; Water or salt in a connector bridging the signal pin to the body; The component itself shorted internally; A harness pinched during earlier repair work.

Check first, cheapest first:

1. Unplug the component and re-read the code — if it changes, the fault is in the component, not the wiring
2. Inspect the loom where it passes metal edges, brackets and hinges
3. Open the connector and check for green corrosion or moisture
4. Measure resistance from the signal pin to a body ground; near-zero confirms the short
5. Repair the harness section, or replace the component if it shorted internally

Related Audi, SEAT, Skoda, Volkswagen codes:

P1231 on Chevrolet (Daewoo)

On Chevrolet (Daewoo) vehicles P1231 is documented as: Fuel pump relay, high voltage. P1231 is stored when the ECU sees signal too high on fuel supply. 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: Open ground for the sensor, letting the signal float up; Signal line shorted to a supply voltage; Sensor failed open, which the module reads as maximum; Connector fault interrupting the return path.

Check first, cheapest first:

1. Read the live value and compare with what the conditions should produce
2. Check the sensor ground continuity back to the module
3. Unplug the sensor: if the reading changes, the wiring is intact and the sensor is suspect
4. Inspect the connector for corrosion or a spread terminal
5. Replace the sensor once ground and signal wiring are confirmed good

Related Chevrolet (Daewoo) codes:

P1231 on Chevrolet (USA)

On Chevrolet (USA) vehicles P1231 is documented as: Injector circuit, cylinder 4 intermittent. P1231 is stored when the ECU sees intermittent fault on fuel injector (cylinder 4). 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: Connector that loses contact with vibration or temperature; Wire broken inside its insulation, making contact only sometimes; Corrosion that conducts until it gets wet or hot; Component failing only under load or at temperature.

Check first, cheapest first:

1. Wiggle-test the loom and connector with live data on screen — the fault has to be caught while it is happening
2. Check freeze-frame data for the conditions that trigger it (temperature, load, speed)
3. Inspect connectors for spread terminals and green corrosion
4. Where possible, monitor the circuit over a drive rather than at idle
5. Replace only the part you have actually seen misbehave

Related Chevrolet (USA) codes:

P1231 on Citroen, Mazda

On Citroen, Mazda vehicles P1231 is documented as: Fuel pump secondary circuit low, high speed. P1231 is stored when the ECU sees signal too low on fuel supply. 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: High resistance in the supply or ground path, dragging the signal down; Corroded connector adding resistance the module reads as a low reading; Sensor drifted out of tolerance with age; Partial short to ground somewhere in the signal line.

Check first, cheapest first:

1. Read the live value on a scanner and compare with a known-good reading
2. Clean and re-seat the connector, then re-test before replacing anything
3. Check the ground point for that circuit — a poor ground causes this far more often than a bad sensor
4. Measure the sensor against specification with the connector back-probed
5. Replace the sensor only once the wiring and ground have been ruled out

Related Citroen, Mazda codes:

P1231 on Ford

On Ford vehicles P1231 is documented as: Fuel pump secondary circuit low, high speed (VLCM). P1231 is stored when the ECU sees signal too low on fuel supply. 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: High resistance in the supply or ground path, dragging the signal down; Corroded connector adding resistance the module reads as a low reading; Sensor drifted out of tolerance with age; Partial short to ground somewhere in the signal line.

Check first, cheapest first:

1. Read the live value on a scanner and compare with a known-good reading
2. Clean and re-seat the connector, then re-test before replacing anything
3. Check the ground point for that circuit — a poor ground causes this far more often than a bad sensor
4. Measure the sensor against specification with the connector back-probed
5. Replace the sensor only once the wiring and ground have been ruled out

Related Ford codes:

P1231 on Mitsubishi

On Mitsubishi vehicles P1231 is documented as: Trustful check active stability control.

Related Mitsubishi codes:

P1231 on Opel / Vauxhall

On Opel / Vauxhall vehicles P1231 is documented as: Fuel pump relay, contact problem; Compressed natural gas relay, open circuit; Compressed natural gas relay circuit, high/low voltage. P1231 points at fuel supply. The standard definition names the system involved; which part inside it has actually failed is what the checks below establish, cheapest first.

Usually one of: Fuel filter blocked; Pump worn and no longer making pressure; Pressure regulator faulty; Wiring or relay fault to the pump; Blocked strainer in the tank.

Check first, cheapest first:

1. Measure actual fuel pressure against specification — this code is about pressure, so guessing without a gauge wastes parts
2. Replace the fuel filter if it is due; it is the cheapest thing in the circuit
3. Check the pump relay and its supply voltage
4. Listen for the pump priming when the ignition is switched on
5. Replace the pump once the filter, wiring and regulator are ruled out

Related Opel / Vauxhall codes:

P1231 on Peugeot

On Peugeot vehicles P1231 is documented as: Control Sleeve Sensor Malfunction. P1231 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 Peugeot codes:

P1231 on Saab

On Saab vehicles P1231 is documented as: Throttle position sensor 1 and 2 circuit, sum out of range, no limp home. P1231 is stored when the ECU sees range or performance on throttle body or pedal position (sensor 1). 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: Sensor reading is inside its electrical range but does not match reality; Contamination or deposits changing what the sensor sees; A mechanical fault upstream that the sensor is correctly reporting; Sensor drifted with age without failing outright.

Check first, cheapest first:

1. Compare the live value against a second sensor or a known-good figure — this code is about plausibility, not a dead circuit
2. Look for the mechanical cause first: leaks, restrictions or wear that would genuinely produce this reading
3. Clean the sensor if it is the type that fouls
4. Check freeze-frame data to see under what conditions it triggered
5. Replace the sensor only after the mechanical side is ruled out

Related Saab 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

P1xxx is manufacturer-specific code (VW/Audi, BMW, Mercedes, Toyota etc. have different meanings for the same code number).

Severity

Manufacturer-specific codes need a brand scanner (VCDS for VAG, INPA for BMW, STAR for Mercedes).

That is what holds for P1231 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.