Powertrain, generic · Ignition system or misfire

P034B Crankshaft Position Sensor - Crankshaft Direction Incorrect

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

Direction-sensing (bidirectional) crank sensors count the rest position for start-stop even when the crankshaft rocks back after shut-off. In normal running the sensor must never report reverse rotation – if it does, the signal is disturbed. GM sets P034B after at least 3 direction reversals within 10 s at 400 to 2,000 rpm and an airflow of at least 1.5 g/s, after two trips; the diesel uses the same thresholds. GM bulletin 17-NA-317 describes the 3.6 V6 (LFY) in the 2018 Buick Enclave and Chevrolet Traverse: interference in the sensor circuit caused P034B with P0506, low idle or stalling after an autostart, transmission slip above 65 km/h and cruise control dropping out; the remedy was a revised sensor wiring. Result: start-stop disabled, possibly reduced power.

Likely causes

Interference in the sensor circuit (wiring routed next to switching lines)
Direction-sensing crankshaft position sensor faulty
Ground or connector fault
Tone wheel or air gap

Symptoms

  • Check engine light on
  • Low idle or stalling after an autostart
  • Start-stop off, possibly reduced power
  • Follow-on effects such as transmission slip or cruise control dropping out (GM LFY)

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–600
Time0.5–3 h

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

Parts involved

crankshaft position sensorsensor wiringengine control module

Related codes

P034AP0335P0336P0506

References: gsi.ext.gm.com, gsi.ext.gm.com, static.nhtsa.gov, patents.google.com.