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Discussion Starter #1 (Edited)
Hi all! I'm sharing steps I went through to repair my car after the CEM was shorted by coolant leak from the heater core pipes.

tl;dr Replace Your Heater core O-Rings.

I was out camping in the desert, luckily with friends. Woke up in the morning, turned on the car.

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The car was on for a bit and then shut off. Very strong burning smell and smoke. Power was cutoff and key was stuck in ignition, tachometer remained on 1600 rpm.


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Inspected the car at home and found heater core pipe leak from failed o-ring/clip at joint.


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CEM significantly burned, spicy, extra crispy. Images of CEM:


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Images of wires and & connector damage:

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Sent burned CEM + BCM + ECM + 1 Key to Xemodex. I figured lower cost "cloning" services not going to have much to clone, and Xemodex has a strong reputation. Units shown for reference:

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Reviewed connectors and fixed burned wires. Got rid of that black box LoJack unit haha.


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Below are photos of wire - CEM 4/56A:14 BK - which completely burned to open the short-circuit in CEM caused by coolant. The burn to open circuit occured between connector and Branching Point 63/12. I'm really glad this wire burned to open circuit, it all could've been much worse fire or damage to the car.

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Discussion Starter #2
<><><><><> continued:

This is Braching Point 63/12, with the wire to CEM burned off and damage all the way to Ground Chassis 31/84.


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This is Ground Chassis 31/67 below right side B-pillar. The wire shows burn/overheat but has continuity. I replaced connector.

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After installing Replacement CEM from Xemodex and replacement o-rings, I kept getting message of Rear Right and Rear Left door open. I inspected the door lock module and and found the circuit burned open.

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After replacing both door lock modules, didn't have any other issues. Car has been driving excellent and I'm glad to keep my S40 on the road. :)


Some resources:

All-in for my specific situation, I paid $948 to Xemodex. They had excellent customer service and the replacement CEM was delivered back "plug-and-play", which was important for me given that the original wouldn't be much use.

Replacement of Heater Core Pipe O-Ring Replacement

Similar situation as reported GoBigRed in this 2017 thread. Seems to be common as these cars are reaching 15+ years.

Out at the beach today.

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Holy crap, I'm not sure that I would ha e gone to the same.lengths to revive my car after seeing that burnt board. Awesome job bringing her back to life!

The fact that this can happen is terrifying, I'm almost tempted to go in and replace those components as a precautionary measure. I've already had my firewall coolant hoses break at the plastic clamps, I imagine the ones in the car aren't too far behind.
 

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Holy f, man, thats incredible its back up and running, the damage looks insane. I just realised, seeing your pic, that the only good thing that comes out of RHD car version, like mine, is that in case of O-ring failure (that I also had), the worse it can happen is to get your clutch pedal wet as CEM is safely tucked on other side of dashboard.
damn..
 

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Very well done! At some point, you may want to replace the o-rings with rubber hoses like a few of us have done.

Love Manhattan Beach!
 
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Great story and thanks for sharing your experience. I have heard of others having their CEMs destroyed by the o-ring leak. I replaced the o-rings in my first V50 and fortunately did not spray the CEM with coolant. On my 2nd V50 I hung a piece of plastic (Zip-lock bag) to block coolant from spraying on the CEM.
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Discussion Starter #8
Thanks all! I believe it's worthwhile to replace the heater core o-rings preventatively if your car is older and you plan to keep it for a while. This is how mine looked:

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On the left is a new o-ring, next to the old o-ring on the right. The failure point is visible.

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This photo is with the new o-rings installed into the heater core lines, before re-assembly. The o-rings and clips are about $40, in hindsight I wish I fixed this beforehand instead of the CEM burning. :ROFLMAO:
 

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Discussion Starter #9
Sharing more detailed photos of burned CEM for reference, and to encourage those with older P1's (like my 2005 S40 T5) to replace the o-rings. :)

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Burns destroyed the connector pins and up to that MCU. CEM cloning not going to be a path here, but Xemodex delivered on a plug-and-play CEM after I sent them my burned CEM + BCM + ECM + 1 Key.

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Where there's smoke, there's a fire. I'm happy to keep my car on the road and had electrical technician-level expertise to fix wiring for the replacement CEM. But fixing all of this specific damage would easily be over $2,500+ all-in at competent shop due to the extensive wiring harness damage.
 

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Okay which o-rings are these- this has me scared- I just cleaned my CEM and that thing has a lot of wires attached
 

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Discussion Starter #11
Okay which o-rings are these- this has me scared- I just cleaned my CEM and that thing has a lot of wires attached
Hi, yeah it's these o-rings:

 
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