My partner left the light on

The tiniest thing causes an obscure fault on a Peugeot van

Published:  05 November, 2012

A Peugeot Partner van arrived at the workshop recently with the owner complaining of a permanently lit airbag light. As the 'bag wasn't hanging out of the steering wheel or anything like that, the first thing I did was to run a quick test on the whole vehicle using the Autologic platform tool. It came up with two fault codes logged in the airbag and nothing else. The faults were:

1. P006F Disarm of passenger airbag

2. P0F40 Van network

With these fault codes not clearing, I decided to test the passenger disarm switch as my first course of action. This tested fine, so I then decided to look at the airbag control unit and do some checks on the airbag ECU. I checked all of the power connections and ground wires which were also good.

Eliminate the obvious

Having ruled out the obvious, my next plan was to check the CAN signals to the control unit using the VM's wiring diagram. I did not see anything obvious on the CAN signal and so decided to check the CAN signals on the other control units as there are two separate multifunction modules. On testing the under bonnet malfunction module I could see that one of the CAN lines was not mirroring the other so I decided to do a wiring check between multifunction module one (BSI) and under bonnet multifunction. Upon doing these checks I found there was a problem with one of the wires somewhere, but the question was, where?

Obscure task

It just goes to show that the tiniest little thing can cause an obscure fault, but using the right test procedure and a bit of patience you can successfully fix them. There are many workshops that seem to employ 'scan-tool jocks' who would be tearing their hair out over a little fault like this - so why not make some easy money and win over delighted customers by developing your skills with the multimeter and oscilloscope? With the airbag and other dash lights now part of the MOT, there is plenty of 'scope' to get involved with simple wiring skills.

Nothing obvious on the control unit CAN signal

One line didn't mirror the other on the under bonnet malfunction module

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