Bad month this month….firstly, the extra money I should have got for working over Christmas has still not arrived – we will be getting it in the March pay (which seems a bit pathetic given other depts got theirs in Jan but still…).

Secondly, the pug was due a service and MOTT – which it actually passed with only a wipe blade \o/. Still cost 250 quid though :-/

As well as that, the C-MAX was in for a service as well. Needed a couple of tyres which I was expecting but other than that is was fine in general (well, 270 quid fine) but there is still one really irritating issue with it – the bloody parking sensors!

For the last month or so, the parking sensors randomly disable themselves with a long beeeeeeeeeeeep. Annoying – and given the front of the car vanishes out of view a bit of a pain when trying to park the bloody thing in small gaps…

This is a 1.8 Ford CMAX ghia with front and rear parking sensors (hopefully, that’ll help others find this from google…). At random times the parking sensors disable themselves with the long beep from the rear which according to the manual means “Refer to dealer”. Ha! Not giving up that quickly.

Given the beep is from the rear, I assume the fault is at the back (an assumption I’ve not yet been able to confirm). Sticking it in reverse gear, ignition on with the electronic parking break off result results in all 8 sensor ticking as I’d expect when they are working – and when I tried this the other morning when it was having a “I’m not going to work” moment it all got a bit more complex…all of the rear sensors appeared disabled (fine) but only 3 of the front ones where working! Odd…

This made be ponder if my assumption of it being a problem with the rears was wrong so having *cough* acquired the ford TIS data CD and noticing that it appears to log a load of codes if there is a parking sensor fault I was pleased to find it buggering about this morning as I was driving past Sams Garage (Wincheap Canterbury – *highly* recommended as the sort of place my dad used to work at – not cheap but excellent) so I dashed in. Stick the thing on their code reader (blimey, these have got a bit more involved since I had anything to do with garages!) and await the codes…..

and wait….

and wait…..

Arse. “Failed to communicate with CANBUS”


Given it’s messing around again, I run around and test the sensors (stick ear near them and a finger gently on them – you should be able to feel a pulsing and hear a gentle tick tick tick) and this time, all for fronts are ticking and the rears are off…

So, I’m not really any further. Sam has pulled the plugs off and checked the connections look ok (on the rear ones at least – front ones appear a bit more involved :-/ ). The diags on his computer appear unwilling to talk to the onboard computer (which may or may not have a fault code logged).

I have some diag data from Ford now that gives me a few test voltages and resistances to check out but beyond that, I’m a bit screwed I think. Ford prices on the sensors are 34-40 quid a piece and the rear module is just shy of a 100 quid – given the local dealers habit of randomly swapping bits till it works I’m reluctant to drop it in there and cough up a few hundred quid but it’s getting to the point where I’m not having much choice (I suppose pulling the bloody speaker off to stop the beeeeeeeeeeeeps and just ignoring it is an option).


Still, hopefully I’ve spread enough key words around this so that google will find it and send me others with a similar problem – please post a comment or email me on if you have *any* information on how to debug this further (or even if it’s driving you mad as well!).

I’m really going off of cars

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1 Response to

  1. Graham says:

    I’ve just read your blog re your parking sensors on your c-max. Sounds very much like the problem i’ve had with mine.

    I bought my c-max second hand in Jan/Feb 08. As soon as I noticed the problem we took the car back to the dealer to fix. It has now been in 3 times and they still haven’t managed to get the sensors working. They think it may be a faulty sensor, I think they don’t have a clue.

    If you find out any more, please could you let me know.

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