Intermittent No-Start on a 2016 Diesel Ute After Rain
A 2016 2.8 L common-rail diesel ute is towed in with a customer report of three no-starts in the past two weeks, each occurring on wet mornings. On two occasions the engine cranked normally but did not fire; once it fired after 20 seconds of cranking. The workshop has already replaced the battery (12.7 V at rest, 10.9 V during cranking) and cleaned the battery terminals. Today the engine starts first turn. Stored codes show P0335 (crankshaft position sensor circuit) as 'history' and no current codes. Freeze-frame data for the P0335 event shows 180 rpm, coolant 12 degrees C, and 0 km/h. The customer needs the vehicle back within two days and has already paid for the battery, which was not the fault.
1. Explain how you would confirm whether the crankshaft position sensor circuit is the true cause, and what evidence would make you look elsewhere.
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A history code with a matching freeze frame (180 rpm means the PCM saw cranking speed, then lost the signal) is a lead, not a conclusion. First, inspect the sensor and its connector for moisture ingress, corrosion, chafed loom near the bellhousing, and correct air gap or debris on the reluctor. Second, perform a voltage-drop and resistance test on the signal and ground circuits while flexing the loom, because an intermittent open will not show on a static meter reading. Third, use a lab scope to capture the crank signal during a cold, damp start; look for dropouts, irregular amplitude, or noise. Fourth, review live data for cam and crank synchronisation. If the scope trace is clean across multiple cold starts and the fault only appears with moisture, suspect connector sealing or loom routing, not the sensor itself. Evidence that would redirect me: a clean trace with a simultaneous fuel-pressure or immobiliser event, low rail pressure at cranking, or a code set only when the engine is hot, which points away from the crank circuit. I would document each test rather than replace the sensor on the strength of a history code alone.
2. The customer is frustrated about the unnecessary battery. Draft the key points you would communicate, and state what you would record in the job file.
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Communication: acknowledge the cost and explain plainly that the battery tested serviceable and was not the cause, so the original fault remains under investigation. State what has been done so far, what the next test is (cold-start scope capture and circuit flex test), and the realistic timeframe against the two-day deadline. Avoid blaming the previous technician; focus on the process. Offer to discuss options if the sensor and connector reseal do not resolve it. Job file: record battery test results (12.7 V rest, 10.9 V cranking), the P0335 history code and freeze-frame values, the tests performed and their outcomes, customer authorisation for further diagnosis, and the commitment made on timing. Note the customer's concern about the battery charge and any goodwill decision. This protects both parties if the fault recurs and supports a clear invoice narrative.