We start checking the fuel pump switching circuit by assessing the integrity of the EF16 fuse (15A), located in the mounting block of the engine compartment.
We replace the defective fuse with a new one, after checking if there is a short circuit in the right (in the direction of travel) 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 type 906.3747-30.
For this purpose, you can use the K7 power window relay.
If the fuel pump turns on with the newly installed relay, the fuel pump relay is bad and needs to be replaced.
Otherwise, check the power circuit and control circuit of the fuel pump relay.
To check the control circuit of the relay and the power circuit of the fuel pump, we remove the relay from the mounting block.
We measure the voltage between socket "30" of the mounting block and "ground".
The device should fix the voltage equal to the voltage of the on-board network.
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".
With a good ground circuit, the device should detect a resistance of less than 1 ohm.
With the ignition on, we measure the voltage between socket "86" of the mounting block and "ground".
The device should detect a voltage of about 12 V.
If this does not happen, we check the health of the circuit between socket "86" and terminal "K54" of the ECU harness block.
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 disassembly of the fuel module).
We measure the voltage between the leads of the brown wire with a white stripe ("+" pump power) and the "mass" black wire adjacent to it.
When the ignition is turned on for 2 s, the device should detect a voltage equal to the voltage of the on-board circuit.
Otherwise, we check the serviceability of the circuits between the "87" socket of the mounting block and the brown wire terminal with a white stripe of the fuel module wiring harness block, as well as between the "ground" and the black wire terminal of the fuel module wiring harness block.