Intermittent Stall With Crankshaft Sensor Code
A 2016 2.0 L petrol car with 98,000 km stalls intermittently when hot, usually at idle after 20–30 minutes of driving. It restarts after 15–20 minutes and runs normally. The only code is P0335 (crankshaft position sensor A circuit). When cold, a lab scope on the CKP signal at the ECM shows a clean 5 V square wave with no dropout; when the engine is warmed to 85°C, the signal drops to 0 V for about 200 ms just before the stall. The sensor’s resistance is 1.1 kΩ cold and 1.9 kΩ hot; the workshop manual gives 0.8–1.5 kΩ at 20°C. Wiggle-testing the sensor pigtail and harness from sensor to ECM produces no change. The reluctor looks clean through the sensor hole, and the sensor air gap is at the upper limit of specification. Battery voltage and grounds at the ECM are good. The customer has already bought a replacement ECM from an online seller.
1. Explain what the scope trace and resistance readings indicate and why the ECM is unlikely to be the cause.
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Scope evidence: The CKP signal is clean when cold but drops to 0 V for about 200 ms when hot, immediately before the stall. That is a loss of the input signal, and it correlates with the stall. A 200 ms dropout is long enough for the ECM to lose crank synchronisation and shut down injection and ignition.
Resistance evidence: The sensor is 1.1 kΩ cold, which is inside the 0.8–1.5 kΩ specification, but 1.9 kΩ hot, which is outside it. That is a classic thermal drift pattern: the sensor behaves when cool and fails as it heat-soaks.
Why not the ECM: Wiggle-testing the harness produces no change, the reluctor is clean and the ECM supplies and grounds are good. The scope is showing the signal dropping at the ECM input, so the ECM is responding to a lost input rather than inventing a fault. The P0335 is a symptom code, not proof of an ECM failure. The customer-supplied ECM should not be fitted on this evidence.
2. State the next tests and the repair and verification plan, including how you would handle the customer-supplied ECM.
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Next tests: Check the sensor reference voltage and ground at the connector when hot, confirm the air gap is within specification, and inspect the reluctor for cracks or debris. If needed, heat the sensor carefully with a heat gun while scoping the signal to reproduce the dropout; do not overheat nearby components. Check the harness for rub-through or heat damage, but the wiggle test already makes wiring less likely.
Repair: Replace the crankshaft position sensor with the correct part, clear codes and road-test to full operating temperature, including idle periods. Monitor CKP signal and live data for stall or dropout. Confirm hot restart and no returning P0335.
Customer-supplied ECM: Explain that the evidence points to the sensor, not the ECM. Do not fit the online ECM as a diagnostic guess; incorrect programming or mismatched immobiliser data can create new faults. Return it or keep it as the customer’s property, and document that fitting it was not recommended.