P1645 — 11 documented meanings by make

P1645 does not mean the same thing on every car — manufacturers reuse the number for different faults. 14 makes document it: Audi, Chrysler, Citroen, Ford, Honda, Hyundai, Kia, Lexus, Mazda, Peugeot, SEAT, Skoda, Toyota, Volkswagen. Find your make below.

P1645 on Audi, SEAT, Volkswagen

On Audi, SEAT, Volkswagen vehicles P1645 is documented as: Drive train data bus, no messages from four-wheel drive control unit. P1645 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, Volkswagen codes:

P1645 on Chrysler

On Chrysler vehicles P1645 is documented as: Wait to start light (glow plug display).

Related Chrysler codes:

P1645 on Citroen

On Citroen vehicles P1645 is documented as: Speed limiter fault (LVV); Fuel pump resistor switch circuit; Acceleration pedal point of resistance information. P1645 is stored when the ECU sees below threshold 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: The monitored part has degraded rather than failed; An upstream fault is loading the part beyond its design; Sensor used to judge the threshold is itself inaccurate; Normal wear reaching the end of its service life.

Check first, cheapest first:

1. Fix any other stored codes first — this class is very often a consequence, not a cause
2. Verify the sensors that judge the threshold before replacing the expensive part
3. Check for leaks or restrictions that would make a healthy part read as failed
4. Compare readings before and after the component
5. Replace the component once it is proven to be the one that has degraded

Related Citroen codes:

P1645 on Ford, Mazda

On Ford, Mazda vehicles P1645 is documented as: Fuel pump resistor switch circuit. P1645 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 Ford, Mazda codes:

P1645 on Honda

On Honda vehicles P1645 is documented as: MOTFSB signal.

Related Honda codes:

P1645 on Hyundai

On Hyundai vehicles P1645 is documented as: Capacitor 1 voltage, booster voltage too high/low. P1645 is stored when the ECU sees signal too low 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: 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 Hyundai codes:

P1645 on Kia

On Kia vehicles P1645 is documented as: Capacitor 1V malfunction. P1645 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 Kia codes:

P1645 on Lexus

On Lexus vehicles P1645 is documented as: Body ECU malfunction. P1645 is stored when the ECU sees malfunction on control module. 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 Lexus codes:

P1645 on Peugeot

On Peugeot vehicles P1645 is documented as: Speed limiter fault (LVV); Acceleration pedal point of resistance information. P1645 is stored when the ECU sees below threshold 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: The monitored part has degraded rather than failed; An upstream fault is loading the part beyond its design; Sensor used to judge the threshold is itself inaccurate; Normal wear reaching the end of its service life.

Check first, cheapest first:

1. Fix any other stored codes first — this class is very often a consequence, not a cause
2. Verify the sensors that judge the threshold before replacing the expensive part
3. Check for leaks or restrictions that would make a healthy part read as failed
4. Compare readings before and after the component
5. Replace the component once it is proven to be the one that has degraded

Related Peugeot codes:

P1645 on Skoda

On Skoda vehicles P1645 is documented as: Drive train data bus, no messages from 4WD control unit. P1645 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 Skoda codes:

P1645 on Toyota

On Toyota vehicles P1645 is documented as: Body ECU. P1645 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 Toyota 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 P1645 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.