Powertrain, generic · Ignition system or misfire

P034C Ion Sense System Performance

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

With ion current sensing the spark plug serves as a sensor after the spark: a measuring voltage across the gap drives a current through the ions in the flame, from which the module detects combustion, misfire and knock – a Delphi patent describes coils with built-in ion sensing, and Saab's Trionic engines detected misfire this way. P034C means this measuring system works implausibly, so misfire and knock detection are no longer reliable. It is documented on the Alfa Romeo Giulia and Stelvio 2.9 V6 biturbo, where three bulletins fix it mainly with engine software; limp mode is possible. Sooted plugs or a faulty coil with ion circuit are further causes.

Likely causes

Engine software or calibration
Spark plugs sooted, oily or wrong type or gap
Ignition coil or cassette with ion circuit faulty
Wiring or connector of the ion current return line

Symptoms

  • Check engine light on
  • Limp mode or reduced power possible
  • Often nothing noticeable otherwise

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€100–600
Time0.5–2 h

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

Parts involved

ion sense systemignition coilsspark plugs

Related codes

P0300P0325P0351P0316

References: static.nhtsa.gov, static.nhtsa.gov, static.nhtsa.gov, patents.google.com.