P1645

P1645 on a Volvo is Fuel Pump Speed Control Range/Performance — on modern Volvos with a returnless variable-speed fuel pump, the ECM commands pump speed via a PWM signal (0-100% duty cycle) to the FPCM (fuel pump control module), and the FPCM reports back actual pump current draw (5-15A typical at moderate load, spiking to 18-20A at WOT on T6 direct-injection). P1645 sets when commanded duty and reported current diverge past threshold, or when the FPCM reports an open/short on the pump motor circuit. Cheapest-first ladder: (1) Read live data — scan tool should show 'Fuel Pump Duty Cycle' and 'Fuel Pump Current'; a duty cycle pinned at 100% with current below 3A means an open circuit (wiring or motor), and a duty cycle ramping normally with current spiking past 18A at idle means a mechanically failing pump dragging on its bearings. (2) Check the top-of-tank connector — on Volvo T6 turbo direct-injection cars, the fuel pump module's main connector at the top of the tank is a known wiring-chafe point where the harness rubs the body opening; pull the access cover under the rear seat or trunk floor, inspect the wires for chafe-through, and ohm the pump motor (should read 0.5-2 ohms across the motor terminals). (3) Test FPCM ground and B+ feed before condemning the module. (4) If the connector and wiring are clean, the FPCM ($180-$350) is more likely to fail than the pump itself ($400-$700) on these cars. Do NOT drop the tank and replace the pump on the first scan — on 2010-2018 XC60 T6 / S60 T6 / XC90 T6 cars, the top-of-tank connector wiring chafe is the most common P1645 cause and the fix is a $0-$30 wiring repair, not a $700 pump.

Vehicle-specific patterns: 2010-2018 Volvo XC60 T6 / S60 T6 / V60 T6 with the B6304T turbo direct-injection 6-cyl is the most common P1645 platform — the fuel pump module wiring at the top-of-tank connector chafes against the body opening on cars with 80K+ mi, and Volvo issued internal service guidance on the wire-routing fix. 2003-2014 Volvo XC90 (2.5T or V8) throws P1645 less often because the older port-injection systems use a simpler constant-pressure pump, but when it does it's usually FPCM failure. 2008-2016 Volvo S80 T6 with the B6304T also shows the top-of-tank chafe pattern. 2015-2022 Volvo XC90 T6/T8 (second generation, SPA platform) has a different pump architecture and rarely throws P1645 — when it does, suspect the high-pressure pump on the direct-injection rail, not the in-tank lift pump. Estimated repair: $0-$50 (top-of-tank wiring repair + heat-shrink) to $900 (full pump module + FPCM + tank drop labor).