P0337 Generic (SAE)

Crankshaft Position Sensor A Circuit Low Input

Updated 2026-10-02 · Ignition system & misfires

Severity

High

Typical repair cost

60 – 500 EUR

System

Powertrain

What it means

The ECM receives too few pulses, or pulses of too low amplitude, from the crankshaft position sensor compared with the camshaft reference or with what engine speed should produce. This is the sensor that times fuel injection and spark, so a weak or missing signal can stop the engine or prevent it from starting. Causes range from wiring to a damaged reluctor ring.

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Symptoms

Engine stalls intermittently, often when hot
Extended cranking or no-start
Check engine light, sometimes with misfire codes
Tachometer drops to zero or flickers while running
Jerking or sudden power loss at speed

Common causes

Failing crankshaft sensor with heat-sensitive internal break (classic hot stall)
Sensor air gap too large due to loose mounting, wrong shim or worn bracket
Damaged, cracked or missing teeth on the reluctor ring or flexplate
Metal debris stuck to the sensor tip from a failing bearing or flexplate
Chafed wiring or corroded connector lowering signal amplitude
Excessive crankshaft end play or a slipped harmonic balancer ring moving the trigger wheel

How to diagnose

Identify sensor type: 2-wire inductive (magnetic) or 3-wire Hall. Inductive sensors produce AC voltage; Hall sensors need 5 V or 12 V supply and output a square wave.
For an inductive sensor, measure coil resistance (typically 200-1500 ohm depending on make) and AC output while cranking: a good sensor produces at least 0.5-1 V AC at cranking speed, rising with RPM. Below 0.3 V points to a weak sensor or excess air gap.
For a Hall sensor, confirm supply (5 V or 12 V) and ground at the connector, then scope the signal pin while cranking; expect a clean 0-5 V square wave with a visible missing-tooth gap each revolution.
Check the air gap where adjustable (commonly 0.5-1.5 mm) and inspect the sensor tip for metal filings or oil sludge.
Inspect the reluctor ring or flexplate teeth with a mirror or borescope for cracks, bent teeth or a shifted ring; compare the scope pattern for irregular tooth spacing.
Wiggle-test the harness with the engine idling while watching the RPM PID; apply heat to the sensor with a hot-air gun to reproduce a hot-stall fault.

Frequently asked questions

Why does the car start fine cold but die when warm?

Heat expands a hairline crack inside the sensor winding or the Hall chip, opening the circuit. Once it cools, the connection closes and the engine restarts. Replace the sensor.

Can P0337 be caused by a bad battery or starter?

A very slow crank from a weak battery can drop an inductive sensor's output below threshold and set a low-input code during start. Fix the starting system first, then clear and retest.