2008 s60: CEM-DD00, CEM-DD01 Headlights go ON and OFF, Fuel filler door open/close

kseyoum · Post by **kseyoum** » 15 Nov 2021, 20:25

Hi All,

I have a 2008 S60 2.5T FWD with 91K miles with a the following problem.

Intermittently, the headlights would come ON and OFF, the fuel filler door would open and then close, and the dash digital readings go dim and then brighten up. I cannot reproduce the problem at will, but it happens sporadically.

The codes from VIDA are CEM-DD00, CEM-DD01. The descriptions are "Communication between LSM control module and CPM control module". Frankly, I don't know where the CPM is.

Thinking that the problem might be the LSM, I swapped it with a known good one, and the problem persisted. The CEM is new and programmed. And VIDA insists that the problem is either a short or an open circuit, and not the CEM.

Does anyone know what and where the CPM is? If you can help me trace the wires, I'd really appreciate it.

Post by **RickHaleParker** » 15 Nov 2021, 20:50

kseyoum wrote: ↑15 Nov 2021, 20:25 Frankly, I don't know where the CPM is.

Combustion Preheater Module (CPM) . The Green-White wire is the signal wire.

kseyoum · Post by **kseyoum** » 16 Nov 2021, 10:07

Thank you, Rick! That's very helpful.

I looked quickly under the left bumper and found a connection point that includes the 'green-white' wire. There is also a 'green-white' wire at the LSM (middle wire). I presume the same wire connects at the CEM - I'll access the CEM and check when time allows. What appears to be a CPM is behind the bumper- which I will remove if I still need access to it the CPM.

Thanks again!

kseyoum · Post by **kseyoum** » 16 Nov 2021, 13:18

Actually, there is no CPM behind the bumper. The connection point for the CPM actually terminates there and is capped. But it is a good testing point.

I did a quick check of 'continuity' between the green-white wire at the 'CPM' connection and the green wire at the LSM - they are connected. However, the green-white wire at the LSM is also connected to the brown wire at the LSM. Is that a short?? It would be really great is someone can confirm that for me.

If there is a short, it will have in the wiring harness under the wiper cowl. I will need to make time to access the harness and the CEM...

Post by **RickHaleParker** » 16 Nov 2021, 15:32

kseyoum wrote: ↑16 Nov 2021, 13:18 However, the green-white wire at the LSM is also connected to the brown wire at the LSM. Is that a short?? It would be really great is someone can confirm that for me.

The ground wire on the LSM is Brown. You can confirm this by checking Brown to chassis ground.

The Green-white passes through the CEM on its way to the CPM ( C:32 and D:41 of the CEM ). If you if you remove the CEM and probe for shorts at the CEM connectors, you could narrow down the short to the CPM side, LSM side or a internal CEM short.

kseyoum · Post by **kseyoum** » 17 Nov 2021, 10:57

Thanks for the additional info, Rick!

Checked the brown wire - and yes it is connected to ground, and the same for the green-white wire - which I think is the source of my problem. I will make time to access the CEM over the weekend and check thoroughly.

Just a note: I understand now why the CEM overrides the LSM when there is a fault in the LSM (my case). The CEM turns on the headlights, opens the fuel filler door, and leaves the dash digital readouts in a dim state (still visible). The front and rear fog lights are not as important, so they are disabled. I would say Volvo thought of this well... I had turned off my daylight running lights, by the way.

-Cheers!

kseyoum · Post by **kseyoum** » 22 Nov 2021, 18:25

Well...

Weird thing is that the problem has not occurred for the last 4 to 5 days. My intent was to open up the CEM over the weekend. I don't know if there is any benefit removing the CEM and probing it while the system is in "working" order. Frankly, I prefer the problem comes back so I can have a known and permanent fix. I will update...

Post by **RickHaleParker** » 22 Nov 2021, 19:14

kseyoum wrote: ↑22 Nov 2021, 18:25 My intent was to open up the CEM over the weekend. I don't know if there is any benefit removing the CEM and probing it while the system is in "working" order. Frankly, I prefer the problem comes back so I can have a known and permanent fix. I will update...

Yea wait until it comes back. One cannot find what does not exist in the here and now.

Do not open the CEM, at least not at first. Remove the CEM and set it aside. That opens the circuit between the LSM and CPM side. How you can probe the wiring harness on each side and isolate which side the problem is on, if it is not the CEM. Then probe the pins on the CEM, the fault might show up on a un-powered CEM. The schematic above shows where to probe.

If that does not do it, open the CEM and look for bad solder joints and something that can be causing a short. Sometimes a connector pin will come loose and intermittent. Could be something rolling around in the CEM like a solder bead ... ect.