We begin checking the fuel pump activation circuit by assessing the integrity of fuse EF16 (15A), located in the engine compartment mounting block.
We replace the faulty fuse with a new one, having first checked whether there is a short circuit on the right one (in the direction of travel) output of the fuse socket to ground.
A malfunction in the fuel pump switching circuit may be caused by damage to the K9 pump relay in the mounting block.
To check the relay…
…we remove it from the mounting block and replace it with a known good one of type 906.3747-30.
For this purpose, you can use the K7 window lift relay.
If the fuel pump turns on with the newly installed relay, then the fuel pump relay is faulty and must be replaced.
Otherwise, it is necessary to check the power circuit and the control circuit of the fuel pump relay.
To check the relay control circuit and the fuel pump power circuit, remove the relay from the mounting block.
We measure the voltage between socket "30" of the mounting block and the "ground".
The device should record a voltage equal to the voltage of the vehicle's electrical system.
If this is not the case, the mounting block is faulty.
We also measure the resistance between the socket "85" of the mounting block and the ground.
If the ground circuit is in good condition, the device should record a resistance of less than 1 Ohm.
With the ignition on, measure the voltage between socket "86" of the mounting block and the ground.
The device should record a voltage of about 12 V.
If this does not happen, we check the serviceability of the circuit between socket "86" and terminal "K54" of the ECU harness connector.
If the circuit is OK, the ECU is faulty.
We install the relay in place and disconnect the wiring harness block from the fuel module (see Removal and disassembling the fuel module).
We measure the voltage between the terminals of the brown wire with a white stripe (the "+" power supply for the pump) and the adjacent black "ground" wire.
When the ignition is turned on, the device should record a voltage equal to the voltage of the on-board circuit for 2 seconds.
Otherwise, we check the serviceability of the circuits between the socket "87" of the mounting block and the terminal of the brown wire with a white stripe of the fuel module wiring harness block, as well as between the "ground" and the terminal of the black wire of the fuel module wiring harness block.