CEM related issues: My diary of ongoing findings...

[moorgate]

(ahem) There is an unconsidered possibility. Speaking as a computer networks nerd, I am reasonably familiar with failures of twisted-pair wiring. If no amount of buggering about with pins and modules is working out then the fault may be a snapped twisted-pair conductor, back somewhere in the wiring loom. Something like 30% of the old computer leads I 'encounter' have at least one conductor (of eight) snapped in the middle of the lead. This makes for very intermittant fault patterns, because normal vibration can bring the snapped ends back into contact, and most twisted pair current loads are so low that the lead then looks kosher. If the snap in the conductor is close to the plug, then Volvo's fix of a replacement connector with a few cm's of 'tail' left on would fix the problem; likewise the chap here who mentioned putting a ferrite core on the twisted leads - the core could be holding the snapped conductor together.

[Clan]

Originally Posted by moorgate

(ahem) There is an unconsidered possibility. Speaking as a computer networks nerd, I am reasonably familiar with failures of twisted-pair wiring. If no amount of buggering about with pins and modules is working out then the fault may be a snapped twisted-pair conductor, back somewhere in the wiring loom. Something like 30% of the old computer leads I 'encounter' have at least one conductor (of eight) snapped in the middle of the lead. This makes for very intermittant fault patterns, because normal vibration can bring the snapped ends back into contact, and most twisted pair current loads are so low that the lead then looks kosher. If the snap in the conductor is close to the plug, then Volvo's fix of a replacement connector with a few cm's of 'tail' left on would fix the problem; likewise the chap here who mentioned putting a ferrite core on the twisted leads - the core could be holding the snapped conductor together.

They are very robust multi strand flexible cables for automotive use , they never give trouble doing their digital job .. the metal terminals on the end where they mate with the pin in the CEM is the weak point . Having said that the vast majority of the volvos have no problems at all .

[Crazybob]

So.......thought I'd update.

Having exhausted my options of a cheap fix I bit the bullet and prayed on a journey down to Volvo Diagnostics in Tilbury. 1 ½ A4 sheets of fault codes later, it turns out the CEM was frazzled caused by an overcharging alternator, when revving the engine the voltage was climbing in excess of 15v. I was expecting a CEM, not an alternator as well, so that stung a little. I am however, glad to have a car without a disco dashboard once again 😁

[Markos01]

Originally Posted by Crazybob

So.......thought I'd update.

Having exhausted my options of a cheap fix I bit the bullet and prayed on a journey down to Volvo Diagnostics in Tilbury. 1 ½ A4 sheets of fault codes later, it turns out the CEM was frazzled caused by an overcharging alternator, when revving the engine the voltage was climbing in excess of 15v. I was expecting a CEM, not an alternator as well, so that stung a little. I am however, glad to have a car without a disco dashboard once again 😁

Great result Crazybob, in terms of getting to the bottom of this. New CEM and alternator then? Out of interest, how painful was it on the wallet?!

[Tbird111]

This article has helped me a lot. My car has two faults; the first; the blower doesn't work, the codes are;
CCM(Climate Control Module) 5 problems exist
1.CCM-0071 Damper Motor. Faulty Position
2.CCM-E010 Power Supply. Faulty Signal
3.CCM-0004 Passenger Compartment Temperature Sensor. Signal
Too High Or Signal Missing
4.CCM-DD14 Recirculation Damper Motor. No Communication
5.CCM-DD10 Air Quality Sensor (AQS). No Communication
We thought that we had narrowed it down to a faulty resistor but according to Volvo the car doesn't have a physical resistor.
The second fault sends it into Limp mode;
1.ECM-0380 Glow Plug Relay. Faulty Signal, but folk say that it probably isn't the relay but the 60amp fuse.
I would be most grateful if I could find the help and clear the problem, thanks,

[aquacultureman]

Originally Posted by Turbodave

Just to update this...

Since my first post and having removed the CEM completely, split it and gently filed the pins with the wife's foam backed nail file and then cleaned the board, the pins and the multi-plugs (again) with contact cleaner and a toothbrush, reassembled, cleared the codes... a couple of months and about 5,000 miles have passed and thus far, it's been fine with no CEM related issues to report.

Granted, I've probably now jinxed it and it'll pack in tomorrow but given it was giving issues on a fairly regular basis, whilst I can't say it's fixed fixed, it certainly appears better. Whether it was filing the pins or another clean or the plugs / pins are sitting better or all of the above, who knows...

Until it happens again, I'm not inclined to start fiddling with it again.

Watch this space...

Excellent article. Particularly since Im current having the same issue! When you say you split the CEM, do you mean you opened it up to clean the circuit board itself? Thanks in advance.

[Parknest]

I've just read this thread from the beginning and it partly relates to my own "anti-skid service required" issue as I have a CEM 1A64 error code.

@moorgate mentioned broken CANbus wires and my first thought was to test the wiring with an oscilloscope. These can be had for a reasonable price these days and it is a good way of checking the integrity of the CANbus network. A simpler test is to check the resistance of the network (60 Ohms if I remember correctly). If you get 120 Ohms then one of the terminating resistors that are located at each end of the network has failed. I think the resistors can be embedded in a module.

I have a Haynes for my own XC90 but the wiring diagrams aren't of much use when you're trying to diagnose problems with modules or the CAN network. I did manage to locate a proper wiring diagram for the P2 platform (V70, XC70 & XC90) which has helped me.

Volvo Diagnostics seems to have a good reputation going by the forum posts that I've read and would be worth a try.

[aquacultureman]

Originally Posted by Clan

This has been going on for over 10 years now occasionally on random S40/V50/C70 / C30 cars , every dealer should know what to do by now .

There are three twisted pairs of digital network communication wires going to the CEM through different plugs , the female terminals in the plugs fret and loose their grip on the CEM pins , volvo do the repair terminals . By rubbing the protective tin off the cem pins you are going to make things even worse .

Hi Clan. Can you tell me the colours of the multiplugs that the twisted Comm wires go into? Also dont know which pins the wires connect to without unravelling the lot!

[Clan]

Originally Posted by aquacultureman

Hi Clan. Can you tell me the colours of the multiplugs that the twisted Comm wires go into? Also dont know which pins the wires connect to without unravelling the lot!

Yes i can ...

plug G ( labelled FRONT 2 ) green , underside on left

pins G14 ( Blue/red ) and G15 Grey/red )




Plug F ( labelled FLOOR 2 ) brown plug to the right of the above green plug


pins F14 (Blue/Red) F16 (Grey/Red)



Plug B ( labelled Cockpit 2 ) , Blue plug top left

pins B8 (Grey/Blue) B9 ( Blue/Yellow )


repair terminals 30656678

you will have to take the plug shells off and replace the terminals with new stronger ones otherwise you get the problem back .

[aquacultureman]

Originally Posted by Clan

Yes i can ...

plug G ( labelled FRONT 2 ) green , underside on left

pins G14 ( Blue/red ) and G15 Grey/red )




Plug F ( labelled FLOOR 2 ) brown plug to the right of the above green plug


pins F14 (Blue/Red) F16 (Grey/Red)



Plug B ( labelled Cockpit 2 ) , Blue plug top left

pins B8 (Grey/Blue) B9 ( Blue/Yellow )


repair terminals 30656678

you will have to take the plug shells off and replace the terminals with new stronger ones otherwise you get the problem back .

Thank you very much Clan. Stupid question - if I order 6 terminals from Volvo, will they already be twisted into their constituent pairs, or is that something I need to do? I notice that Skandix supplies them as single wires, and am vaguely aware of the electromagnetic interference reason for twisting.