P0321 Code: Engine Speed Input Signal Out of Range

🟠 Moderate severity · drivable

Drivable, but the engine may run rough, misfire, or stall, so get it checked soon.

What P0321 means

The engine computer is receiving a signal that tells it how fast the engine is spinning, but the signal values are out of the expected range. On most cars this speed signal comes from the crankshaft position sensor, and on older cars from the distributor. Without a clean speed reading, the computer can't time the spark and fuel correctly.

Symptoms

Check engine light is on
Rough running or misfire
Hard starting
Engine stalling

Common causes

most common: Faulty crankshaft position sensor
common: Damaged wiring or loose connector at the sensor
less common: Worn distributor pickup on older cars
rare: Damaged reluctor ring or flywheel

How to fix it

Fix	DIY?	Typical cost
Inspect and clean the sensor connector and wiring	Yes	$0–10
Replace the crankshaft position sensor	Yes	$50–200
Have a shop test the engine speed signal with a scan tool	Mechanic	$80–150