What does it mean?
P1320 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: ICM 4X Reference Circuit No Pulses (Intermittent) .
Symptoms
- MIL (check engine lamp) on
- Intermittent stalling, typically when the engine is hot, followed by a normal restart once it cools
- Extended cranking or an occasional no-start
- Cutting out or stumbling while driving, sometimes over bumps
- Tachometer needle dropping or jumping while the engine is running
Likely causes
- Intermittent open or chafe in the 4X reference wire between the ignition module and the engine control module
- Damaged, contaminated or misaligned crankshaft position sensor and reluctor wheel
- Failing ignition control module output stage, often heat sensitive
- Corroded, loose or heat-damaged connector pins at either module
- Poor ignition module ground: many of these modules earth through their mounting bracket, which corrodes
- Electrical noise from a failing secondary ignition component corrupting the pulse train
How to fix it
- Read the freeze frame and note engine temperature and rpm when the fault set; heat-related failures are common on this circuit
- Monitor rpm in live data and wiggle-test the ignition module harness looking for dropouts
- Inspect the module mounting surface and ground path, clean any corrosion and retighten to specification
- Check the 4X reference wire end to end for continuity and for shorts
- Where a scope is available, capture the reference signal under load and look for missing pulses
- Inspect the crankshaft sensor tip and the reluctor ring for metal debris, damage and correct air gap
- Replace the ignition control module only after the wiring, ground and crank sensor have been proven