P0335: Crankshaft Position Sensor Circuit — Diagnosis, Causes & Testing

What the code means

P0335 is a circuit / signal code for the crankshaft position sensor. The ECM has detected that the crankshaft position signal is missing, implausible, or intermittent — it cannot reliably determine engine speed and TDC position. Many ECMs will not trigger fuel or ignition without a valid crank signal, so P0335 is a common cause of crank-no-start.

System involved

• Crankshaft position sensor (CKP) — inductive (2-wire), Hall (3-wire), or VR types
• Reluctor / trigger wheel on the crank (tone ring, missing-tooth wheel)
• Sensor power, ground, and signal circuits (Hall) or signal/return (inductive)
• Air gap between sensor and reluctor

Common symptoms

• Crank-no-start (engine cranks but will not fire)
• Tachometer does not move during cranking
• Stalling, especially when hot
• Hard start, long crank
• MIL on
• Intermittent no-start that clears when cool

Possible causes

• Sensor failure: internal open or thermal breakdown (classic hot-stall)
• Wiring: open or shorted signal, power, or ground; chafing near the engine
• Connector: heat damage, pins spread, corrosion
• Air gap: too large → weak signal; too small → sensor damage / contact
• Reluctor/trigger wheel: damaged teeth, foreign material, loose ring
• EMI: signal corruption from nearby high-current wiring
• ECM input: rare

Why the DTC does NOT prove a particular component has failed

P0335 reports that the crank signal is unreliable. It does not say whether the sensor is dead, the wiring is broken, the air gap is wrong, or the reluctor is damaged. A thermal-failure sensor, a chafed wire, a damaged trigger wheel, and EMI all set the same code. Replacing the crank sensor because "P0335 is the crank sensor" is the parts cannon — a chafed harness or a damaged reluctor will produce the identical code and the new sensor will not fix it.

Initial checks

1. Read all codes. P0340 (cam correlation), P0300 (misfire), P0336/0337/0338 (CKP variants).
2. Tachometer during cranking: does it move? No movement strongly suggests no crank signal reaching the ECM.
3. Does it fail hot only? Thermal-failure sensors pass cold tests.
4. Visual: connector, wiring near the sensor and along the engine harness.

Freeze-frame values worth reviewing

• Engine speed during cranking (0 or erratic = no signal)
• Coolant temperature (hot-only failures)
• Whether the code set during crank or while running

Live-data parameters worth reviewing

| Parameter | Why | |---|---| | Engine speed during cranking | Should read ~150–300 RPM; 0 or erratic = no signal | | Crank signal sync status (if available) | ECM confidence in the signal | | Cam / crank correlation | Synchronisation status | | Engine speed stability while running | Dropouts reveal intermittent signal |

Electrical tests

• Hall (3-wire): power (5V or 12V), ground, and signal. Back-probe during cranking; a Hall sensor should produce a clean square wave.
• Inductive (2-wire): resistance across the sensor (compare to spec); AC voltage during cranking.
• Signal with oscilloscope: the decisive test — a clean, consistent waveform vs a corrupted, dropout, or missing waveform.
• Wiring continuity and short-to-ground/12V.

Mechanical tests

• Air gap between sensor and reluctor — compare to specification. Vehicle-specific verified specification required.
• Reluctor inspection: damaged or missing teeth, foreign material, loose trigger wheel.
• Sensor tip for damage from contact.

Next-best-test decision logic

1. Does the tach move during cranking? → No: likely no signal. → Yes but code sets: intermittent / hot. Continue.
2. Power/ground/signal at the sensor (Hall)? → Missing power/ground: wiring. → Present: continue.
3. Oscilloscope waveform during cranking? → Clean: signal reaches ECM — check ECM input/reluctor. → Corrupted/missing: sensor, air gap, or reluctor. Continue.
4. Air gap correct? → No: adjust/replace. → Yes: continue.
5. Reluctor intact? → Damaged: reluctor. → Intact: sensor.
6. Fails hot only? → Heat-test the sensor; thermal failure common.

Common diagnostic mistakes

• Replacing the sensor without an oscilloscope confirmation.
• Not testing at the temperature the fault occurs (hot failures pass cold).
• Ignoring the reluctor/trigger wheel.
• Overlooking EMI from nearby high-current wiring.
• Not checking the air gap.

Related DTCs

• P0340 — Camshaft position sensor (correlation with crank)
• P0336 / P0337 / P0338 — CKP circuit variants
• P0300 — misfire (crank signal noise can corrupt misfire detection)
• P0016 / P0017 — crank/cam correlation

Manufacturer-specific considerations

• BMW: inductive CKP on many N-series, thermal failures known; reluctor ring integrity. Vehicle-specific verified specification required.
• Audi / VW: Hall/inductive variants across engines; wiring near exhaust heat. Vehicle-specific verified specification required.
• General: an oscilloscope trace is the single most decisive test.

Driveability and safety considerations

• A no-start leaves the vehicle stranded — tow if hot-stall is recurring.
• Stalling in traffic is a safety risk.
• Do not continue driving with an intermittent crank signal; it can stall without warning.

Example evidence-driven diagnostic workflow

1. Complaint: "Stalls when hot, then crank-no-start for 20 minutes, then starts again."
2. Scan: P0335. Clears when cool.
3. Hypothesis: thermal crank-sensor failure.
4. Test 1 — Cold: starts and runs; scope waveform clean.
5. Test 2 — Hot stall: tach drops to 0 during crank; scope waveform missing.
6. Test 3 — Power/ground at sensor (hot): present. Sensor itself dropping out.
7. Confirmed root cause: crank sensor thermal failure.
8. Repair: replace crank sensor.
9. Verification: hot restart reliable; clean scope waveform at temperature; no code return.

The reluctor, air gap, and wiring were all confirmed good first — the sensor was the cause, but only after thermal scope testing proved it.