Crankshaft Position Sensor "A" Circuit Intermittent

Possible causes

• CommonFailed crankshaft position sensor - very often one that works cold and fails hot
• CommonCorroded, oil-contaminated or damaged connector at the sensor
• CommonChafed or heat-damaged wiring - the sensor sits low on a hot engine
• PossibleMetal debris on the sensor tip
• PossibleDamaged, loose or misaligned reluctor ring on the crankshaft
• PossibleStretched timing chain or slipped belt changing the signal relationship

What you might notice

• Engine cuts out while driving and will not restart until it cools
• Long cranking, or no start at all
• Rev counter dead or erratic while cranking
• Stalling at idle
• Check engine light on

What to check, in order

1. Take this seriously even though the car may be driving normally now. An engine that stops while moving takes the power steering assistance and brake servo with it.
2. Note the conditions - hot, over bumps, or in the wet. Heat points at the sensor, bumps at the wiring, wet at the connector.
3. Wiggle-test the harness with the live data screen showing engine speed.
4. Note whether the fault is heat-related. A sensor that works from cold, fails after twenty minutes and works again an hour later is the classic crankshaft sensor failure, and that pattern is worth more than any measurement.
5. Inspect the connector for oil contamination and corrosion. These sensors sit low on the engine where oil leaks find them.
6. Check the wiring for chafe and heat damage along its run.
7. Inspect the sensor tip for metal debris.
8. Watch engine speed on the live data screen while cranking. No reading confirms the signal is genuinely absent rather than merely poor.