OBD-II Fault Code

P1309: Misfire Monitor AICE Chip Fault

Meaning, symptoms, likely causes, diagnostic checks and repair guidance for P1309.

System family

Powertrain

Manufacturer-specific

Repair category

Engine misfire

Use this category to narrow your checks before replacing parts.

Severity

High

Severity is a general guide. Confirm with scan-tool data and vehicle symptoms.

What P1309 usually means

Misfire Monitor AICE Chip Fault.

Common symptoms

Check Engine light, rough idle, hesitation, flashing MIL if severe

Likely causes

Worn spark plug; Faulty ignition coil; Injector or fuel issue; Vacuum leak; Low compression

Diagnostic checks

Scan all modules and record freeze-frame data before clearing codes; Check battery voltage and related fuses; Identify affected cylinder(s), inspect plugs/coils, check fuel trims and compression if needed

Repair guidance

Swap-test coil/injector where practical, replace worn ignition parts, repair vacuum/fuel/compression cause

Verification after repair

Clear code, road-test through the same drive condition, then rescan; Confirm misfire counters remain at zero during road test

Note: Confirm vehicle make/model/year because manufacturer-specific codes can vary; Manufacturer-specific: confirm definition and test steps in the vehicle service manual. A DTC identifies a circuit or system condition, not always the failed part.