Powertrain, generic · Ignition system or misfire

P034A Crankshaft Position Sensor - Crankshaft Start Position Incorrect

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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.

Likely causes

Direction-sensing crankshaft position sensor faulty or aged
Interference pulses in the sensor circuit during shut-off
Air gap or tone wheel – teeth not detected at low speed
Engine module software

Symptoms

  • Check engine light on
  • Start-stop restricted or off
  • Delayed or rough autostart
  • Rarely stalling after an autostart

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–500
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

crankshaft position sensorcrankshaft tone wheelsensor wiringengine control module

Related codes

P034BP0335P0336P0315

References: gsi.ext.gm.com, gsi.ext.gm.com, patents.google.com, patents.google.com.