P0373

P0373 means the PCM is seeing the high-resolution timing reference signal (often the CKP-B or secondary crankshaft sensor on engines that run a redundant pair) but the pulses are arriving intermittently or with erratic spacing — missing edges, doubled edges, or jitter outside the ECM's tolerance window. Cheapest-first ladder on the shop floor: (1) wiggle-test the CKP-B harness with the engine idling while watching scan-tool RPM-B / cam-correlation live data — if RPM stutters or drops momentarily, you've already found the bad connector or chafed wire. (2) Scope the signal at the sensor connector — a Hall-effect CKP-B should produce a clean 0-5V square wave with crisp rising edges at cranking (300+ pulses/sec at 200 rpm cranking on a 58-tooth wheel), and a VR (variable reluctance) sensor should produce a 0.5-1.5V AC sine that grows to 5-15V peak-to-peak at 2,500 rpm. Ragged baselines, missing teeth that aren't the synchronization gap, or amplitude under 0.4V at cranking on a VR sensor all confirm sensor or air-gap problems. (3) Pull the sensor and inspect the tip for ferrous debris — VR sensors are magnets and they collect timing-cover swarf that bridges the air gap and corrupts the waveform; wipe with a clean rag and retest before condemning the part. (4) Inspect the reluctor/tone ring on the crankshaft for chipped teeth or a bent flange — a single bent tooth shows up on the scope as one bad edge per crank revolution and reads as 'intermittent erratic.' Expensive-misdiagnosis caveat: before you order a $300 CKP-B sensor, check the alignment of the reluctor wheel — on engines that share a timing-cover-mounted sensor (Ford 6.0L Powerstroke, GM Duramax LB7), a stretched timing chain or a worn cover bushing lets the reluctor wobble axially, producing intermittent pulses that look exactly like a bad sensor; replacing the sensor without correcting the chain/cover lasts about a week before P0373 returns.

Vehicle-specific patterns: 2003-2010 Ford 6.0L Powerstroke (F-250/350, Excursion) commonly throws P0373 alongside P0341/P0344 because the CMP and CKP-B share heat-soak failure modes on the front timing cover — the connector pins corrode from oil-vapor blow-by and the signal drops at hot idle; reseating with dielectric grease buys time but the proper fix is a sensor + pigtail. 2001-2010 GM Duramax LB7/LLY/LBZ throws P0373 when the camshaft position correlation drifts — same redundant-timing-reference architecture, and the CKP-B sits on the engine block exposed to road spray; the harness chafes against the bracket and the signal goes intermittent during cold-soak starts. 2007-2009 Mercedes M642 BlueTec 3.0 V6 diesel (Sprinter, GL320, ML320, R320 BlueTec) frequently throws P0373 from a known CKP wiring harness rub-through near the bell-housing — the wire insulation cooks against the exhaust manifold and shorts intermittently. 2009-2014 BMW N57 3.0 inline-6 diesel throws P0373 typically from a failing crank sensor itself (Bosch units that go non-linear at temperature). Estimated repair: $180 to $850.