P034ACrankshaft Position Sensor - Crankshaft Start Position Incorrect
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- Engines with start-stop or hybrid autostart store the crankshaft rest position when the engine stops, so that they can inject and fire correctly at once on restart. This needs a direction-sensing crank sensor, because a cylinder under compression can push the crankshaft backwards after shut-off. On restart the module compares the stored position with the one actually measured after the reference gap. GM sets P034A when they differ by more than 2 teeth in 2 of 3 autostarts or by at least 1 tooth in 4 of 5, after two trips; the diesel already at more than 1 tooth in 1 of 3. The check is suspended while a crank sensor fault is present. Result: start-stop is restricted, restarts take longer with conventional synchronisation, and the autostart may be rough.
- What you may notice
- Check engine light on
- Start-stop restricted or off
- Delayed or rough autostart
- Rarely stalling after an autostart
- Likely causes
- LikelyDirection-sensing crankshaft position sensor faulty or aged
- PossibleInterference pulses in the sensor circuit during shut-off
- PossibleAir gap or tone wheel – teeth not detected at low speed
- RareEngine module software
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €80 – €500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.