P0320 to P0322: ignition and engine speed input circuit

Everything the engine management system does is timed against crankshaft position. Injection, ignition, cam control, misfire detection — all of it needs to know exactly where the crank is and how fast it is turning.

P0320 to P0322 mean that input became unreliable or disappeared.

Code	Meaning
P0320	Ignition/distributor engine speed input circuit malfunction
P0321	Range/performance
P0322	No signal

Closely related, and often present together: P0335 crankshaft position sensor diagnostics.

The symptom that identifies it

A sudden stall while driving, with an immediate restart that sometimes works and sometimes does not.

That pattern — running one moment, dead the next, no warning, no rough running beforehand — is characteristic. The ECU lost its timing reference and stopped injecting.

Engine stalls while driving causes covers the wider set of causes for the same symptom.

The second characteristic symptom: cranking with no start, where the engine turns normally and never fires. Without the signal, the ECU does not know when to inject.

Engine cranks but won’t fire.

The heat-related version

Worth its own paragraph because it is common and confusing.

A crank sensor that is breaking down internally often works cold and fails hot. The car drives for twenty minutes, stalls, refuses to restart, and then starts perfectly after half an hour standing.

Owners describe this as “it needs to rest”. What is actually happening is that the sensor’s windings or electronics fail above a temperature threshold and recover as they cool.

If your fault has that shape, the sensor is a strong candidate even if it tests fine cold.

Causes

The sensor

Most common. Inductive sensors fail with age and heat; Hall sensors fail electronically. Either way, replacement is the fix.

The reluctor or tone ring

The toothed wheel the sensor reads. Damage, a cracked ring, or debris in the teeth produces an erratic signal that reads as a range/performance fault rather than a total loss.

On some engines the ring is part of the flywheel, which makes this an expensive finding. Check it before assuming the sensor: P0336 crankshaft sensor range/performance.

Air gap

Sensors mount at a specified distance from the ring. Debris, a disturbed mounting or a bolt not fully tightened changes that gap and degrades the signal.

Wiring

The sensor lives low on the engine, near heat and in the path of oil leaks. Chafed insulation and oil-contaminated connectors are both common.

Shielded cable matters here. These are low-level signals, and a repair made without maintaining the shield can produce intermittent faults that defy diagnosis.

Camshaft sensor interaction

Some engines can start using the camshaft signal alone if the crank signal is lost, and others cannot. On vehicles that can, the symptom is a long crank rather than a no-start, which is a useful distinction.

P0340 camshaft position sensor.

What to log

Engine RPM from the live data during a stall event is the definitive capture, if you can get it.

A healthy signal shows RPM falling smoothly as the engine slows. A sensor fault shows RPM dropping to zero instantly while the engine is still physically turning — the signal disappeared, the engine did not stop.

That distinction, caught once, ends the diagnosis.

Diagnosing intermittent faults with OBD.

Do not overlook the simple causes

Before condemning a sensor on an intermittent stall:

• Check the battery and its terminals. A poor connection can drop voltage enough to reset the ECU mid-drive, which looks identical from the driver’s seat.
• Check the earth straps. Engine-to-body earths corrode, and a poor earth affects low-level signals first.
• Check for aftermarket wiring. Alarms and trackers spliced into the ignition circuit are a recurring cause of unexplained stalls: aftermarket accessories electrical faults.

Sequence

1. Characterise the fault — hot only, cold only, random?
2. Check battery terminals and earth straps.
3. Inspect the sensor connector and the harness for oil and chafing.
4. Log RPM and try to capture a stall.
5. Inspect the reluctor ring if the signal is erratic rather than absent.
6. Replace the sensor with an OE-quality part — cheap crank sensors are a known source of repeat failures.

Try it on the free tier of the app — pair an ELM327 adapter and leave RPM logging on a car that stalls unpredictably. Catching that signal drop once is worth more than a week of guessing.