P0321
PowertrainIgnition/Distributor Engine Speed Input Circuit Range/Performance
Usually a small job, often just a £30 to £80 sensor and an hour's labour, but you shouldn't ignore it because the car can cut out on you. The ECU watches the crankshaft position sensor to time the spark and injection, and when that signal goes erratic or drops out of its expected window, it throws P0321. On a lot of cars it sits in the same family as the more common P0335, so don't be surprised if both show up together.
ⓘ Information only. This page provides general educational information about fault code P0321. 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 P0321 mean?
P0321 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Ignition/Distributor Engine Speed Input Circuit Range/Performance.
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:
- • Long cranking before it catches, or the odd refusal to start at all
- • Engine cutting out at idle or low revs, sometimes restarting fine a minute later
- • Rough running and misfire you can feel through the seat
- • Flat spots and hesitation when you put your foot down
- • Engine warning light on, often the first thing you notice
- • A sudden stall while driving, which is the symptom that makes this code worth taking seriously
Possible causes
Causes commonly associated with P0321, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Failing crankshaft position sensor, the usual suspect. They get heat-soaked over the years and start dropping their signal when hot, which is why so many of these faults are intermittent
- 2. Damaged or corroded wiring and connectors at the sensor plug, common where the loom runs near the gearbox or down by the block and cops road salt
- 3. Worn or oil-contaminated reluctor ring (tone wheel) on the crank, so the sensor reads a dirty or uneven pattern
- 4. Poor earth or a loose pin in the connector causing a dropout under vibration
- 5. A camshaft sensor playing up on engines where the ECU cross-references the two signals
- 6. Electromagnetic interference upsetting the signal, something a few older VAG petrol engines were known for
- 7. A failed ECM, but this is rare and the last thing to suspect, not the first
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 stored codes, not just this one. A P0335 or a cam sensor code (P0340) alongside P0321 points you straight at the timing signal circuit and tells you a lot before you touch a spanner
- 2. Get to the sensor and check the connector and wiring properly. Unplug it, look for green corrosion, broken pins, oil contamination, and chafed insulation where the loom rubs the block
- 3. Back-probe the connector and check the signal with a multimeter or a scope. Most crank sensors are either inductive (an AC voltage that climbs with cranking speed) or Hall-effect (a switching square wave). Compare against the manual figures for your engine
- 4. Wiggle-test the loom and connector with the engine running, or warm the car up if the fault only shows when hot. Intermittent dropouts are nearly always heat or vibration related
- 5. Inspect the reluctor ring for missing teeth, debris, or oil if you can see it, especially if the car has a known oil leak in that area
- 6. If the wiring and signal check out but the code keeps coming back, fit a quality sensor and clear the adaptations. Replacing it blind without checking the loom first is how people end up buying two sensors
Common questions about P0321
Can I keep driving the car like this? +
I wouldn't make a habit of it. The crank signal is what the ECU uses to fire the engine, so when it goes erratic the car can stall without warning, which is no joke pulling out at a junction or sat in fast motorway traffic. If it's running well enough to get home or to a garage, fine, but don't plan a long trip on it. Park it and sort the fault if it's already cutting out.
Is this going to be an MOT problem? +
Not the code itself, the tester can't read your stored faults. What fails you is the engine warning light being on at the time of the test, which counts as a major defect. Fix the cause, clear the light, drive a few miles so it stays off, then go for the MOT. If you turn up with the MIL glowing you'll fail before they even start the emissions check.
What's the damage to put it right? +
For a straightforward sensor swap at an independent you're usually looking at £80 to £180 all in, the part being £30 to £80 and the rest labour depending on how buried it is. A main dealer will often be £200 to £350 for the same job with their hourly rate and a genuine sensor. If the fault turns out to be wiring or a corroded connector, a decent garage can repair that for similar money. The bills only climb if the reluctor ring is worn, since that's a much bigger job.
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 →