P1931 — 3 documented meanings by make

P1931 does not mean the same thing on every car — manufacturers reuse the number for different faults. 6 makes document it: Audi, Ford, Mazda, SEAT, Skoda, Volkswagen. Find your make below.

P1931 on Audi, SEAT, Skoda, Volkswagen

On Audi, SEAT, Skoda, Volkswagen vehicles P1931 is documented as: Cooling fan control unit false function. P1931 points at control module. The standard definition names the system involved; which part inside it has actually failed is what the checks below establish, cheapest first.

Related Audi, SEAT, Skoda, Volkswagen codes:

P1931 on Ford

On Ford vehicles P1931 is documented as: Fuel additive pump control circuit/open. P1931 is stored when the ECU sees open circuit 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: Broken wire, most often at a flex point such as a door hinge or engine mount; Corroded or pushed-back terminal in the connector; Blown fuse on the supply side; Component failed with an internally open winding or element.

Check first, cheapest first:

1. Check the relevant fuse first — it is the cheapest thing that produces this code
2. Unplug and inspect both halves of the connector for corrosion and terminal fit
3. Continuity-test the wire end to end while flexing the loom by hand
4. Measure the component itself against its specification
5. Repair the break or replace the component, whichever the measurement points to

Related Ford codes:

P1931 on Mazda

On Mazda vehicles P1931 is documented as: Fuel additive pump control circuit high. P1931 is stored when the ECU sees signal too high 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: 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 Mazda 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 P1931 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.