P1491 — 11 documented meanings by make

P1491 does not mean the same thing on every car — manufacturers reuse the number for different faults. 15 makes document it: Audi, Chrysler, Citroen, Ford, Honda, Isuzu, Mazda, Mercedes-Benz, Nissan, Peugeot, Saab, SEAT, Skoda, Subaru, Volkswagen. Find your make below.

P1491 on Audi, SEAT, Skoda, Volkswagen

On Audi, SEAT, Skoda, Volkswagen vehicles P1491 is documented as: Activated charcoal filter system solenoid 2, N333, open circuit. P1491 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 Audi, SEAT, Skoda, Volkswagen codes:

P1491 on Chrysler

On Chrysler vehicles P1491 is documented as: Radiator fan relay control circuit. P1491 points at cooling system. The standard definition names the system involved; which part inside it has actually failed is what the checks below establish, cheapest first.

Related Chrysler codes:

P1491 on Citroen, Mazda, Peugeot

On Citroen, Mazda, Peugeot vehicles P1491 is documented as: Secondary switch solenoid circuit.

Related Citroen, Mazda, Peugeot codes:

P1491 on Ford

On Ford vehicles P1491 is documented as: Evaporative emission system vacuum cut/bypass solenoid malfunction. P1491 is stored when the ECU sees malfunction on evaporative emissions system. 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: Fuel cap not sealing or the wrong cap fitted; Cracked or perished breather hose; Purge valve stuck open; Charcoal canister split; Leaking tank seal around the pump flange.

Check first, cheapest first:

1. Refit the fuel cap firmly, clear the code and drive for a few days — a surprising share of these are the cap
2. Inspect the visible EVAP hoses for cracks and loose clamps
3. Command the purge valve with a scanner and listen for it clicking
4. Smoke-test the system if the simple checks find nothing — a small leak is very hard to see

Related Ford codes:

P1491 on Honda

On Honda vehicles P1491 is documented as: Exhaust gas recirculation, exhaust gas recirculation valve insufficient lift. P1491 points at EGR system. 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: Valve stuck with carbon deposits; Cooler blocked or leaking; Vacuum or electrical control fault; Position sensor reading wrongly.

Check first, cheapest first:

1. Remove the valve and inspect for carbon — cleaning fixes a large share of these
2. Command the valve with a scanner and watch whether it moves
3. Check the vacuum line or electrical connector depending on the type fitted
4. Replace the valve if it will not move when commanded and cleaned

Related Honda codes:

P1491 on Isuzu

On Isuzu vehicles P1491 is documented as: EFG valve lift insufficient detected.

Related Isuzu codes:

P1491 on Mercedes-Benz

On Mercedes-Benz vehicles P1491 is documented as: Refrigerant pressure in air-conditioning system too high. P1491 is stored when the ECU sees signal too high on air conditioning / climate. 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 Mercedes-Benz codes:

P1491 on Nissan

On Nissan vehicles P1491 is documented as: Vacuum cut/bypass valve.

Related Nissan codes:

P1491 on Saab

On Saab vehicles P1491 is documented as: Evaporative emission system, fuel level sensor; Evaporative emission system, tank pressure sensor. P1491 points at evaporative emissions system. 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 cap not sealing or the wrong cap fitted; Cracked or perished breather hose; Purge valve stuck open; Charcoal canister split; Leaking tank seal around the pump flange.

Check first, cheapest first:

1. Refit the fuel cap firmly, clear the code and drive for a few days — a surprising share of these are the cap
2. Inspect the visible EVAP hoses for cracks and loose clamps
3. Command the purge valve with a scanner and listen for it clicking
4. Smoke-test the system if the simple checks find nothing — a small leak is very hard to see

Related Saab codes:

P1491 on Subaru

On Subaru vehicles P1491 is documented as: PCV (blow-by) malfunction. P1491 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 Subaru 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 P1491 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.