Citroen berlingo VSS signal

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Citroen berlingo VSS signal

Postby Avdr » Thu Jan 09, 2014 3:48 pm

Had a job come in on a citroen berlingo. 2001, 2.0hdi RHY engine.
Customer says speedo isn't working but occasionaly the needle flicks up for a moment before dropping back down, as this happens the engine hesitates.

I traced the wiring back from VSS (no ABS) on gearbox output, getting a good square wave there. Next I pulled a wiring diagram, and this is where it thickens, I've found two diagrams which conflict. One suggests the signal goes through the multifunction control module then onto the engine ECU as a square wave, but that the signal is transmitted to the instruments on a VAN bus.

Another diagram suggests the signal simply splits from VSS to go to instruments and engine ECU as a square wave.
Neither diagram had the correct pin laypout for ECU - both show one big connector when infact I've got 3 smaller ones - not a good start.

Anyway I found the wire for VSS in the ECU plug by probing each in turn until I got continuity back to the VSS. The square wave on this wire exactly matches that at the VSS - so I'm happy with that. But I'm stuck now for the instrument side of things. Non of the wires to the instruments has continuity to the VSS. The stupid numbers they put on the wires don't match up to the diagram (no big shock).

I've ran a test on the speedo itself and it completes a series of movements when commanded to by the tool, so the stepper motor and control side of things would seem ok, for the test functionality atleast.

Has anyone come across this and able to shed some light on the wiring lay out?

Thanks
Avdr
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Re: Citroen berlingo VSS signal

Postby Avdr » Sat Jan 11, 2014 2:44 pm

Think I've made some more sense of the wiring diagrams. The one long ECU connector appears to be a bosch approach. Where as the 3 small ones are listed under a siemens management system. I will verify which is fitted and carry on working through.
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Re: Citroen berlingo VSS signal

Postby Avdr » Mon Jan 13, 2014 1:04 pm

Got it sorted. The ECU was indeed a siemens. You have to pretend its a citroen Xsara to get the correct wiring diagram from autodata.

I started looking at the signal from VSS again and it had gone, then it came back but was all distorted. Found a bad earth in the end, there was an issue between VSS and earth point 2.

Rectified that and all is well.
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