P0321 Ignition/Distributor Engine Speed Input Circuit Range/Performance

P0321 points to a range or performance problem in the ignition or distributor engine speed input circuit. The signal may exist, but it is not matching expected speed, timing, or quality.

Code details

Generic OBD-II · P0

System: Ignition / Misfire
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not treat P0321 as a simple no-start code only; intermittent or distorted engine speed signals can also cause stalls and misfire-like symptoms.

Symptoms of P0321

Rough idle, shaking, or a stumble under acceleration.
A flashing check-engine light during an active misfire.
Power loss and higher fuel consumption.

Common causes of P0321

Worn spark plugs, ignition coils, or plug wires.
Fuel-delivery problems — injectors, pressure, or a lean/rich mixture.
Vacuum leaks, low compression, or a mechanical fault in that cylinder.

Useful checks before replacing parts

Compare commanded and measured RPM, crank or distributor signal quality, freeze-frame RPM, sync status, and related crank or cam correlation codes.
Inspect the sensor air gap, reluctor condition, distributor shaft play where applicable, wiring resistance, grounds, and electrical noise sources.
Road-test or heat-soak the vehicle if the signal only becomes implausible under temperature, vibration, load, or higher RPM.

Related OBD-II codes

These nearby ignition / misfire entries can help compare wording and pin down the fault area.