P0335: the crankshaft position sensor — the one the engine cannot start without

A distinctive scenario: the car cranks strongly and evenly but never catches. Full tank, healthy battery, working starter. And nothing.

High on the suspect list is P0335 “Crankshaft Position Sensor Circuit” — one of the few sensors without which the module will supply neither spark nor fuel.

Why it is critical

The control module must know crankshaft angular position to within a degree — otherwise ignition and injection timing cannot be determined.

There is exactly one source for that: a toothed ring on the flywheel or pulley and a sensor facing it. There is no backup.

So the module’s logic is: no signal, no operation. Not “let us approximate”, but total refusal. That is deliberate: firing a spark at an unknown moment is more dangerous than not firing at all.

The camshaft sensor, which behaves completely differently, is covered in the neighbouring article.

Symptoms

• The engine cranks but will not start. The main one.
• Sudden stalling while driving, then refusing to restart until it cools.
• Jerking under load, misfiring.
• The tachometer jumps or sits at zero while cranking.

That last point is a free test: crank the engine and watch the tachometer. A motionless needle means no signal.

The most treacherous scenario: heat-related failure

The classic, and the one that wastes the most time.

The sensor works cold and stops after warm-up. The car starts in the morning, drives, and after a stop refuses to restart for 20–40 minutes. Once it cools, it works again.

People live with this for months while workshops testing it cold find nothing. If the symptom tracks temperature, it is almost always the sensor.

Causes

1. The sensor itself. Unlike many components, here it genuinely ranks first. The magnetic or Hall element degrades with heat.

2. Wiring and connector. The sensor sits low on the engine, in the zone of dirt, moisture, and road salt. Wires chafe, connectors corrode.

3. A contaminated tip. Metal debris from the oil sticks to the magnet and muffles the signal.

4. A damaged reluctor ring. Broken or clogged teeth. Often after clutch or flywheel work.

5. Air gap. After removal and refitting the sensor sits further out than specified. Weak signal, intermittent code.

Why there may be no code

An important point. If the engine will not start, the module may never write a code — some checks only run with the engine running.

So “no codes” on a non-starting car does not clear this sensor. What to look at is live data while cranking: does the module see any RPM at all?

The check procedure

1. Crank and watch the tachometer — a dead needle means no signal.
2. Live data while cranking: zero RPM with the starter turning means the same.
3. Temperature correlation: only fails when hot means the sensor.
4. Inspect the connector and wire at the bottom of the engine.
5. Remove it and look at the tip — debris cleans off in a minute.
6. Check resistance against the manufacturer’s figure if it is an inductive type.

Telling it apart from other no-start causes

Quick triage:

Symptom	Most likely
Cranks, tachometer dead	Crankshaft sensor
Cranks, tachometer works, no catch	Fuel or spark
Does not crank, clicks	Battery or starter
Starts then dies immediately	Immobiliser, fuel

The full set of scenarios is in why a car will not start, and separately in immobiliser troubleshooting.

In short

• Without this sensor the engine fundamentally cannot start — there is no fallback.
• A dead tachometer while cranking is the key free diagnostic.
• “Only fails when hot” is almost always the sensor itself.
• There may be no code, because the engine never ran long enough.
• It takes ten minutes to check with no special equipment.

Download the app — live RPM while cranking is read with an ELM327 adapter over Bluetooth SPP on Android.