P0629

P0629 is the high-side complement to P0628: the FPDM control circuit is reporting battery voltage when the PCM is commanding the line low, or commanded duty cycle is below feedback by more than the manufacturer threshold. In PWM fuel-pump systems the PCM low-side-drives the FPDM control wire; at rest the wire sits near battery voltage (pulled up internally), and the PCM pulls it low to switch the FPDM output on. P0629 sets when the PCM can't pull that line down — either the wire is shorted to a 12V source, the PCM low-side driver has failed open, or the FPDM has internally shorted its control input to its supply. Shop-floor ladder, cheapest first: backprobe the FPDM control wire with a DVOM key-on engine-off; healthy reading is 11-13V with the PCM idle. Then crank the engine while watching: it should drop to 0-2V momentarily as the PCM commands the pump on, with the duty cycle averaging 30-60% during run. If it stays pegged at battery voltage through cranking, disconnect the FPDM connector and check the wire's resistance to chassis ground — anything below 100 ohms is a short-to-power somewhere upstream (almost always chafed against a frame member). Inspect the FPDM connector for green corrosion and bent pins. Expensive-misdiagnosis caveat: P0629 with no fuel pump activity will tempt you toward a PCM replacement, but on Ford trucks the in-tank pump itself has been seen to short its supply line back through the FPDM and pull the control wire high — disconnect the pump at the tank and retest before condemning the PCM, because a $400 pump masquerading as a $1,200 PCM job is a 40% chunk of your margin gone.

Vehicle-specific patterns: 2011-2016 Ford F-150 EcoBoost is the most common P0629 ticket — same frame-rail FPDM as P0628, but the failure mode here is typically internal short rather than corrosion; the FPDM swaps out and the code clears. 2009-2014 Ford F-150 5.0 Coyote and 5.4 Triton share the same FPDM platform and the same failure. 2007-2014 Lincoln Navigator and Ford Expedition with the 5.4L 3V throw P0629 from FPDM internal shorts as the modules age past 100k miles. 2014-2019 RAM EcoDiesel throws P0629 from the under-seat low-pressure pump control module — same root cause, different mounting. 2010-2016 Lincoln MKT / MKS / Taurus SHO with the 3.5L EcoBoost shares the F-150 FPDM and shares its failure curve. Estimated repair: $200 (FPDM replace DIY) to $1,400 (FPDM + pump + harness section + labor).