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Discussion Starter · #1 ·
I've a 2008 159 1.9Jtdm. I've an intermittent fault that is coming up a few times a week. The Hillholder not available error will show and at the same time the reverse parking sensors will come on and stay on.

I can turn the parking sensors off with the ceiling control so it isn't the biggest issue but it is annoying.

I'd assumed it was the brake switch that was the issue but cruise control is fine. Is there a reverse gear sensor/switch that would cause this?
 

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I’d start with the easy stuff first, battery voltage, alternator and all the connections.
 

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As above, but to answer your question, there is a reverse light switch on the gearbox, which is part of the CAN network.

Do your reverse lights work as they should?
 

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Discussion Starter · #5 ·
Okay, inevitably the car has behaved for the last few days but then last night the error occurred again.

The reverse lights stop working when this error occurs, along with the hill holder error and the parking sensors being on at all times.

So it seems it is either the clutch switch or maybe the reverse gear switch on the gearbox.

Having searched on the forum the clutch switch procedure seems surprisingly complex. I'm not clear why the clutch switch would bring the reverse parking sensors on. Can anyone explain that?
 

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It might be that the harness connector on the reversing switch (on top of the gearbox) is failing causing intermittent issues. The switch in my case was fine but the plastic switch housing had completely crumbled allowing the wiring to come loose. My symptoms were slightly different but it’s easy enough to check.
 

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It might be that the harness connector on the reversing switch (on top of the gearbox) is failing causing intermittent issues. The switch in my case was fine but the plastic switch housing had completely crumbled allowing the wiring to come loose. My symptoms were slightly different but it’s easy enough to check.
Hi

Switches are either on or off, their fault condition is very much the same, either always on or always off. At most this should result in a fixed error - i.e. the reversing lights won't come on at all, ever. Bad connections tend to be random.

There is no systematic reason why a reversing switch should affect clutch related functions.

So where unrelated functions appear to fail together the most likely fault is something that they have in common, perhaps in the wiring where the return signal paths meet. So OldSmokeys experience seems to reflect the most likely cause, while wacjacs problem may have been cured by disturbing and reconnecting wiring rather than by the replacement of the switch.

Diagnostics would be improved if people would ask to be given the 'faulty' item, so in wacjacs case if the replaced switch was shown to be good, it would have been eliminated from the diagnosis rather than being blamed as the cause. (I'm not saying it wasn't, just theorising).

I'm having my gearbox done next week - I'm asking to have all the replaced bearings given back to me so that I can better determine what the fault was and so if another member of the forum has a similar problem I can at least offer a checked possible diagnosis.

So Marknewton, you have two suggested causes, a switch or wiring. I'd like to know what was found when you get it fixed - and if a switch was blamed, you might get it back and see if it really was faulty!

Cheers
James
 

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Discussion Starter · #8 ·
Well, I finally got to the bottom of the problem. Not what I had expected at all. I thought I'd post the final solution as I hate threads that don't finish with an answer.

In the end it turned out to be the boot lid wiring loom. Wires splitting in the flexible join. For some reason, the lights there malfunctioning brought on the parking sensors and the hillholder error!?

I only realised as the rear lights in the boot lid stopped working, along with the reversing light. Then the boot button stopped working. A further clue that it was related to the lights was that the parking sensors wouldn't come on all the time, if the lights were switched to off. I usually just leave them on auto. A number of wires had broken, including the earth wires. A number more were frayed and on the way.

I cut out the damaged section and simply used crimp connectors to splice in some multi core mains cable. There are 8 wires going into the boot lid although the earth then splits into a further 4 making 12 on the other side. Confused me at first!

Still, all is well now. I can see backwards when reversing and no more error!
 

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Hi

Thanks for coming back with the answer. It just shows that seemingly unrelated faults that occur together should make you think that something is misleading the electronics rather than each system suddenly becoming illogical and crazy at the same time!

Cheers
James
 
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