P034A code meaning
Crankshaft Position Sensor - Crankshaft Start Position Incorrect
Powertrain system Generic code P03xx codes Check engine light
What P034A means
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.
P034A at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 3 hours
- Clears after repairAfter a drive cycle
Symptoms of P034A
- Check engine light on
- Start-stop restricted or off
- Delayed or rough autostart
- Rarely stalling after an autostart
Common causes of P034A
- Most 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
- Less likelyEngine module software
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Crankshaft position sensorCrankshaft tone wheelSensor wiringEngine control module
What each part of P034A means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 3 | Area: ignition system or misfire. |
| 4A | The exact fault in that area. |
What to do next
- Note P034A and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P034A
What does P034A mean?
P034A means "Crankshaft Position Sensor - Crankshaft Start Position Incorrect". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P034A?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P034A fail an emissions test?
Yes, it can. P034A is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P034A to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will P034A clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.