P0374

P0374 means the PCM is seeing NO pulses at all on the high-resolution timing reference (CKP-B or secondary crank input) — the signal is dead, not intermittent. This is a no-start or hard-start code on engines that require the redundant signal for injection timing. Cheapest-first ladder: (1) key-on-engine-off, backprobe the CKP-B connector and verify reference voltage and ground — a Hall-effect sensor should see 5V or 12V on its supply pin and a clean chassis ground (under 0.1V drop); a VR sensor is passive and has only signal + return, so check continuity between the sensor pins (typical VR coil reads 500-2,000 ohms cold; open or shorted = sensor dead). (2) Crank the engine while scoping the signal wire — zero output during cranking confirms a dead sensor or a broken signal wire upstream. (3) Inspect the sensor tip for impact damage from a separated reluctor wheel or a thrown timing-chain guide fragment; a sheared sensor housing reads dead and looks fine until you pull it. (4) Check the PCM-side connector for corrosion or backed-out pins — on diesel platforms the PCM lives in the engine bay and sees water intrusion through the firewall grommet. Expensive-misdiagnosis caveat: before you replace the CKP-B sensor and start chasing wiring, confirm the reluctor wheel is still on the crank — on Ford 6.0L Powerstrokes and GM Duramax LB7s, a broken keyway on the crankshaft pulley or a sheared reluctor-to-crank pin will produce P0374 with a perfectly healthy sensor and harness; replacing the sensor without pulling the front cover to inspect the reluctor wastes a $300 part and a half-day of labor.

Vehicle-specific patterns: 2003-2007 Ford 6.0L Powerstroke is the most common P0374 ticket in heavy-duty diesel shops — the CMP/CKP-B pair fails together as a heat-cycle wear pattern, and the truck either won't start or stalls at hot idle and won't restart until cool; the fix is sensor + pigtail + reseal at the front cover. 2001-2004 GM Duramax LB7 throws P0374 from the same general cause but commonly via a chafed wire at the harness clip behind the alternator. 2007-2014 RAM 6.7 Cummins commonly throws P0374 when the CKP harness gets oil-soaked from a leaking front main seal — the oil migrates into the connector and breaks continuity. 2009-2015 Mercedes Sprinter OM642 throws P0374 from a brittle sensor housing that cracks at the locating tab during a routine timing-cover R&R. Estimated repair: $220 to $1,100.