Can-bus guru's advice needed please. Topic is solved

Free2drive! · Post by **Free2drive!** » 02 Mar 2017, 02:24

Hello folks

I'm trying to solve an ongoing issue in my 2004 2.4 geartronic Volvo.

Problem is:

Vida says no communication between: CEM, BCM, TCM and ECM. I get anti-skid, brake stop safefely followed by a thud in the transmission.

CEM has been replaced and changed again under warranty. I'm confident it's not the CEM.

Garage said it was a power issue, we changed the battery and the alternator. We changed the ignition switch.

What can I do next?? It won't start...I need to get it running.

Any ideas welcome.

Free2drive! · Post by **Free2drive!** » 02 Mar 2017, 02:24

Forgot to say thanks in advance.
Matthew

Post by **precopster** » 02 Mar 2017, 03:37

BCM can be the next module in the list of replacements however without a scan with Vida we are all just guessing.

Free2drive! · Post by **Free2drive!** » 02 Mar 2017, 08:14

Thanks Precopster, this is the big issue. Vida just says no communication each time.
CEM no communication
BCM no communication
TCM no communication
ECM no communication.

We clear off the codes then restart the car. Then all the messages appear and the dials drop out.
Volvo dealer says Vida won't help to pinpoint the issue because it can't read the modules.

Really stuck with this one.
Matthew

Post by **JRL** » 02 Mar 2017, 09:04

You probably have a broken wire somewhere.
Trial and error, you need to start tracing the each eire, each connection under each module, first the actual connections then if nothing is found, then start tracing the wiring from those four modules to where each wire goes
Start with the ECM

Free2drive! · Post by **Free2drive!** » 03 Mar 2017, 02:25

Thanks JRL.

I spent a few hours yesterday cleaning up the earth contacts. I found a frayed wire on the earth bolted to the front passenger fender. Maybe that was the issue? CEM has been sent off to be checked so I can't start the car yet.

There are loads of earth points. I found damp on the drivers side B pillar, but the wires in that area were dry. Is there an earth point on the B pillars, I couldn't find one?

So battery is new. Contacts all cleaned from trunk through to engine bay. Motor and earth strap cleaned, starter motor and alternator contacts cleaned.

Is there a common connector point for the CEM, TCM, BCM and ECM?
Thanks
Matthew

Post by **yagger** » 03 Mar 2017, 09:50

Do you have a DiCE?

Free2drive! · Post by **Free2drive!** » 04 Mar 2017, 04:57

Thanks Yagger,
No DiCE. I've been getting messages read n cleared at the dealer for $$$. But they finally said they couldn't read anything. On the last visit the car wouldn't even start.
I went back the next day and drove away with no issues until a few miles down the road when it went. Anti skid, brake stop, gearbox thuds and speedo/tacho drop out.
Dealer is perplexed, they are struggling to fix it and say to buy a new CEM then start changing modules for $$'s. I've got a repaired CEM and even had that replaced under warranty just in case but the problem persists.
I am praying I find a broken wire or burnt relay or something before it goes for scrap. I have a little time and some experience fixing cars so I'm giving it a go.
Would having DiCE help pinpoint the issue, if so why haven't Volvo done it?
Matthew

Post by **abscate** » 04 Mar 2017, 08:34

Can a single component failure wipe out the CANBUS protocol? I would not read the lack on communication as meaning multiple failures until I understood this better

Post by **jimmy57** » 04 Mar 2017, 18:47

Drop CEM out of its bracket. On back of CEM you will find multiple green and white wires (CAN network wires for body and propulsion networks, AKA low speed and high speed networks) that are twisted (spiralled) that go into plugs on CEM. Find the twisted green & white pair that goes with harness up and out into engine bay. Probe the green and white with voltmeter with one lead of meter grounded. Those wires should have 2.2 and 2.8 V DC. If shorted to each other then V will be 1.0 to 1.2 usually. If one is shorted to ground then the one shorted will read 0 and the other will read 1.2 V. If shorted to power the one shorted will be 12 +/- V and the other about 1.2 V less than that.

There is no ready access to the back side of connections of other modules and on that model year the diagnostic plug is not direct connection to network wires. You may have a green & white twisted pair under back seat at a connector on floor on left side. You could go there first before accessing wires at CEM. If you find the CAN voltage is 2.2/2.8 w/ignition in position II then the next is to un plug a module and see if problem is gone. You can remove one at a time and then turn on ignition and wait to see if newtork fails. You will have messages/warning lights for the removed module but if a module is the failure then the network communication will stay on and remaining modules will function. Ecm and Bcm are end of line modules. TCM is a jumper for ECM so removing TCM will also disconnect ECM from network. Cem can't be removed as it is master controller of network.