P0337
PowertrainCrankshaft Position Sensor Circuit A Low Input
Most of the time this turns out to be the crank sensor itself going weak, or its wiring getting cooked by engine heat or soaked in oil from a leaking seal. The ECU watches the voltage signal coming back from the crankshaft position sensor as the engine spins, and P0337 means that signal dropped lower than the module expects to see. Since the ECU uses that signal to time the spark and the fuel, a dodgy reading here can make the car a pig to start or stall it dead.
ⓘ Information only. This page provides general educational information about fault code P0337. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0337 mean?
P0337 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Crankshaft Position Sensor Circuit A Low Input.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine turns over fine but won't fire up, or takes several goes before it catches
- • Engine warning light on the dash, sometimes with the car dropping into limp mode
- • Rough, shaky idle that you can feel through the wheel and the seat
- • Random stalling, usually worst at idle or pulling away from a junction
- • Flat spots and hesitation when you put your foot down
- • Rev counter sitting dead or flickering while you're cranking, a classic crank sensor tell
Possible causes
Causes commonly associated with P0337, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Crankshaft position sensor on its way out, the usual culprit. They sit in a hot, dirty spot and the signal weakens as they age
- 2. Wiring or connector at the sensor damaged, corroded, or contaminated. Oil from a leaking crank seal or rocker cover wicking into the plug is very common and gives exactly this low-voltage symptom
- 3. Weak or flat battery dragging system voltage down during cranking, which can make a healthy sensor read low and trip the code
- 4. Tired starter motor turning the engine too slowly for the sensor to produce a clean signal
- 5. Sensor sitting at the wrong air gap, or knocked out of alignment with the reluctor wheel after recent work
- 6. Chipped or missing teeth on the crank reluctor ring, which messes up the pattern the ECU is reading
- 7. Faulty ECU or a calibration that's out of date, rare but worth a thought once everything else checks out
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Pull all the stored codes and write down what's there alongside the P0337. Companion codes like P0335 or P0339 point at the same circuit and help you build the picture
- 2. Get your hands on the sensor and its connector. Look for melted insulation, green corrosion on the pins, and oil in the plug. An oil-soaked connector is a frequent cause and a cheap fix
- 3. Check battery voltage and watch what it does on cranking. If it sags badly the sensor isn't getting a fair chance, sort the battery and starter before condemning anything else
- 4. Back-probe the connector and confirm you've got the reference voltage the manufacturer specs, usually around 5 volts. No reference, you've got a wiring or ECU problem upstream
- 5. Measure the sensor's resistance with a multimeter and hold it against the workshop figures. Way out of range and the sensor's scrap
- 6. If you've got a scope, watch the waveform while the engine cranks. A clean, repeating signal with proper peaks tells you the sensor and trigger wheel are doing their job; a ragged or low trace doesn't
Common questions about P0337
Can I carry on driving while it's showing this code? +
I wouldn't bank on it. The whole point of the crank sensor signal is to keep the spark and fuel timed, so a car throwing P0337 can stall on you without warning, sometimes mid-roundabout. If it's running rough or cutting out, get it home and leave it. If it's currently driving normally and only the light is on, treat it as borrowed time and get it looked at before you find yourself stranded.
Is this going to be an MOT problem? +
The code on its own isn't an MOT line item, but a lit engine warning light is. The MOT now includes a check on the MIL, so if that lamp is glowing when the tester plugs in or eyeballs the dash, expect a fail. Fix the cause, clear the code, and let the light stay off through a drive cycle before you book it in.
What sort of money am I looking at to sort it? +
The sensor itself is usually cheap, often £20 to £80 for a decent aftermarket or OE part. At an independent garage you're typically looking at £80 to £200 all in once you add an hour or so of labour, more if the sensor's awkward to get at. A main dealer will push that toward £250 to £400. If the real fault is damaged wiring rather than the sensor, repairs can climb a bit depending on how much loom has to come apart.
How do I work out whether it's the sensor, the wiring, or just the battery on my car? +
Start with the cheap stuff. Test the battery and watch its voltage on cranking, because a tired battery will mimic a sensor fault and you don't want to buy parts you didn't need. Then get the connector off and inspect it, oil or corrosion in there points straight at wiring rather than the sensor. If the battery's healthy and the plug is clean and dry, measure the reference voltage and the sensor's resistance against spec. A sensor that's out of range is your answer; correct resistance but a bad signal on a scope usually means the trigger wheel or the loom.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →