Cause
Damaged wiring to the pressure regulator
The wiring to a fuel pressure regulator damaged — chafed, crushed or corroded — so the control signal is degraded rather than absent. A partial fault is worse than a clean break, because the regulator responds erratically instead of not at all, and the module chases a pressure that will not settle.
High resistance is the version that hides. The circuit tests as continuous, the regulator moves, and it simply does not move as far as commanded — so pressure hunts, and the codes name performance rather than a circuit. A pressure that oscillates around its target rather than sitting on it is a control fault, not a mechanical one.
These regulators sit on or beside the high pressure pump, in heat and vibration, so the damage is usually where the harness leaves its clip or crosses the engine. Measure voltage drop along the circuit with the regulator operating rather than resistance at rest — that is the only test that finds a joint which is continuous but resistive.
Typically a moderate job.
Codes this can cause (2)
Codes where this is a likely explanation first, rather than merely a possible one.
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