Powertrain, generic · Ignition system or misfire

P038F Ignition J Control Signal Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

Ignition J is one of the control signal lines from the engine module to an ignition module, ignition output stage or group of coils; which cylinders it serves is defined by the manufacturer, not by the code standard. The code concerns the logic-level control signal, not the coil's primary current (that has its own codes, P0351 ff and P2300 ff). P038F means the control line reads high – typically shorted to voltage. No manufacturer using these codes was found – neither GM nor Ford use the Ignition A to J codes; GM reports coil control faults as P0351 ff – so the description follows CARB and that analogy. The affected coils fire wrongly or not at all, causing misfire; many modules then shut off injection to those cylinders to protect the catalyst.

Likely causes

Control line shorted to a supply wire
Ignition module or coil faulty
Moisture or corrosion in the connector
Driver stage in the engine module

Symptoms

  • Check engine light on
  • Misfire, jerking, rough idle
  • Loss of power, possibly cylinders shut off
  • Additional misfire codes P0300 ff

Repair estimate

DifficultyMediumDIY possible
Parts and labour€50–500
Time0.5–2.5 h

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

Parts involved

ignition control jignition moduleignition wiring

Related codes

P038DP038EP0300P0351P2300

References: law.cornell.edu, gsi.ext.gm.com, newtonnet.co.uk.