This 2013 Golf VII 5G1 arrived having been doing the rounds at various garages, trying to solve an SRS fault. Initial scan results showed a fault with the passenger pre-tensioner module A, no communication. The fault code U017E was permanent, with or without the module connected.

The previous workshop had run another wire for the LIN circuit from the SRS module to the passenger pre-tensioner module connector. An unsuccessful attempt was made to code the module, no communication was present.

The technician then checked the power supply into the pre-tensioner module, as well as the ground terminal. Finally, the LIN bus was scoped to check signal integrity. All proved good, so a new module was fitted and communication attempted. Still no joy.

We asked for the power and ground to be tested under load, not just with the connector unplugged. Then the moment of truth, the power feed dropped to 4.2 volts.

The fuse diagram revealed that the SRS was fuse 41 in the interior fuse box, and it should be 25 amp rated. When the technician checked the fuse, it had power both sides of the fuse. On connecting the module, one side of the fuse dropped to 4.2 volts. The fuse was pulled to inspect it and the tech realised it was only a 1-amp fuse. When a properly sized 25 amp fuse was installed, and the module was then communicating and was able to be coded. It later transpired the customer had been playing around fitting a dash camera and had swapped fuses around.

The voltage drop across the 1 amp under load had caused all these issues. The low voltage supply could only be seen when the circuit was under load. Under load, the volt drop across the incorrect rated fuse left only 4.2 Volts supplied to the SRS module, making it incapable of functioning.

This only goes to prove we need to gather all the information from the customer on everything that occurred prior to the issue. Also, start the diagnosis from the beginning. Take no account of previous diagnosis, as this can lead to mis-diagnosis when trusting the results gathered from previous technicians tests.

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