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Corrosion at the fuel pump's electrical connections, dropping enough voltage under load that the motor runs slow. The pump is healthy and it is being underfed — which produces low pressure, low flow and pump performance codes naming a part that does not need replacing.

A meter's continuity check will pass the joint that causes it. Corrosion behaves as a resistance, and resistance only shows as a voltage drop when current flows — so the connection reads fine at rest and collapses when the pump draws its ten or fifteen amps. Measure voltage at the pump connector while the pump runs, comparing it against battery voltage; anything more than a few tenths of a volt short is the fault.

The connections are in a hostile place. The pump's plug sits on top of the tank under the rear seat or the boot floor, where spilled liquid and condensation collect, and its earth is often a body point underneath. A pump replaced without cleaning those joints runs slow too, which is why the second pump seems to fail as quickly as the first.