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CEM / Dipped Beam issue on 2003 V40 Sport.

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Old Jul 2nd, 2019, 15:39   #1
Redr0cket
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Default CEM / Dipped Beam issue on 2003 V40 Sport.

Hi, my dipped beam all of a sudden stopped working, while all other lights are fine. I did some reading on here and thought it sounded like the CEM. I got a used unit off someone on the Facebook group and it seems like the used unit has had a bit of a DIY job on it at some point. It has "headlight Relay x 2" written on it. The lights don't turn off at all while the engine is running/ignition turned, and the internal light switch shown the side lights as on when they are off, and off when they are on. I wondered if this does sound like a DiY mess, or whether I'm missing something. When I put the old one back in all of fine aside from the dipped beam not working. If anyone has a used one in working condition I have placed a post in the wanted section. Thanks.
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Old Jul 2nd, 2019, 17:29   #2
SwissXC90
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It sounds like you have a CEM with a failed relay

You can replace the relays, even the soldered-on relays, with the right tools.
I recommend you fix your own CEM, as that way you have no coding issues.
The CEM is the main brain of the car and the entire car config including VIN etc is stored in the CEM, so fitting one from another care that is coded differently will cause many side effects. A 100% identical CEM with same part number, same software config will work, but the VIN will be wrong. And you cannot check the software config externally.

If you do not have the electronics skills, then contact a repair shop such as the guy in London who can fix your own CEM (at a component level) for you.

See here:
https://volvodiagnostic.com/shop/ind...duct&id_lang=1
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Old Jul 2nd, 2019, 19:48   #3
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Quote:
Originally Posted by SwissXC90 View Post
It sounds like you have a CEM with a failed relay

You can replace the relays, even the soldered-on relays, with the right tools.
I recommend you fix your own CEM, as that way you have no coding issues.
The CEM is the main brain of the car and the entire car config including VIN etc is stored in the CEM, so fitting one from another care that is coded differently will cause many side effects. A 100% identical CEM with same part number, same software config will work, but the VIN will be wrong. And you cannot check the software config externally.

If you do not have the electronics skills, then contact a repair shop such as the guy in London who can fix your own CEM (at a component level) for you.

See here:
https://volvodiagnostic.com/shop/ind...duct&id_lang=1
Thank you for that. While I was pulling mine our and swapping them over I did start to wonder whether it all seemed a bit too simple... 🤣

I have looked at that link and it seems just what I need. I suppose I can use the CEM that isn't working exactly right while I don't have my own.

Do you know if it's possible to "code" a replacement unit, and how much that kind of thing would normally cost?

Thanks again.
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Old Jul 3rd, 2019, 20:01   #4
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As has been said above, AIUI the units are coded to the car so rather than go down that route, buy the relays and replace them.

I did it myself for my S40 and it's not too difficult, providing you've got the right tools in advance.


But before you start taking everything apart, here's a link to a post I wrote about a quick test for your CEM, might help you to diagnose what's happening.

https://www.volvoforums.org.uk/showthread.php?t=272600
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Old Jul 3rd, 2019, 20:47   #5
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Quote:
Originally Posted by Redr0cket View Post
Do you know if it's possible to "code" a replacement unit, and how much that kind of thing would normally cost?
Follow the link I gave you, that guy provides those services.
Volvo do not. They only sell new units.
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Old Jul 6th, 2019, 23:23   #6
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Quote:
Originally Posted by SwissXC90 View Post
It sounds like you have a CEM with a failed relay

You can replace the relays, even the soldered-on relays, with the right tools.
I recommend you fix your own CEM, as that way you have no coding issues.
The CEM is the main brain of the car and the entire car config including VIN etc is stored in the CEM, so fitting one from another care that is coded differently will cause many side effects. A 100% identical CEM with same part number, same software config will work, but the VIN will be wrong. And you cannot check the software config externally.

If you do not have the electronics skills, then contact a repair shop such as the guy in London who can fix your own CEM (at a component level) for you.

See here:
https://volvodiagnostic.com/shop/ind...duct&id_lang=1


That's actually incorrect. The CEM is not coded to the car, or the ECU. Only thing that needs doing is enabling/disabling a few functions such as twin lens or single lens headlights, front Fog lights Enable/disable, DRLs Enable/Disable, Rear Wiper Enable/Disable.

I have repaired many CEMs todate and test every sinle one of them on my car and not once did I have any issues with the CEM not being coded to the car.

On all newer models, post 2004, the CEM is coded to the cars and its harder to get it sorted
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Old Jul 9th, 2019, 14:54   #7
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@ "... That's actually incorrect. The CEM is not coded to the car, or the ECU ..."

Useful to know in case the unit goes u/s.

Thanks for that.
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Old Jul 10th, 2019, 22:55   #8
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Quote:
Originally Posted by gatos View Post
That's actually incorrect. The CEM is not coded to the car, or the ECU. Only thing that needs doing is enabling/disabling a few functions such as twin lens or single lens headlights, front Fog lights Enable/disable, DRLs Enable/Disable, Rear Wiper Enable/Disable.

I have repaired many CEMs todate and test every sinle one of them on my car and not once did I have any issues with the CEM not being coded to the car.

On all newer models, post 2004, the CEM is coded to the cars and its harder to get it sorted

Thanks Gatos 😉
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Old Jul 15th, 2019, 21:53   #9
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I have a 52-plate V40 with one headlight failed on low-beam. Reading the forum points to CEM - I've changed bulbs, fuse, bulb holder as old one looked fried. (Everything else is fine, except engine management light has a mind of its' own - off for a month, on for a day/week/month as it feels - usually close to MOT time - and then off again..could this be related?) I do have a soldering iron but have only used it to replace a couple of pots on an old Hi-Fi amp that didn't really matter so butchering my CEM worries me. From your reply Gatos, a breakers yard CEM with the correct part No. will do the job just fine, if I can find one? That would give me more confidence to open mine up. I can't really send it away to the chap in London as, even with perfect postage, I'd be a week without the car.
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Old Jul 16th, 2019, 09:42   #10
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Quote:
Originally Posted by Scimdaz View Post
I have a 52-plate V40 with one headlight failed on low-beam. Reading the forum points to CEM - I've changed bulbs, fuse, bulb holder as old one looked fried. (Everything else is fine, except engine management light has a mind of its' own - off for a month, on for a day/week/month as it feels - usually close to MOT time - and then off again..could this be related?) I do have a soldering iron but have only used it to replace a couple of pots on an old Hi-Fi amp that didn't really matter so butchering my CEM worries me. From your reply Gatos, a breakers yard CEM with the correct part No. will do the job just fine, if I can find one? That would give me more confidence to open mine up. I can't really send it away to the chap in London as, even with perfect postage, I'd be a week without the car.
Your car, being a 2002, should most probably have a CEM with part number 30621305. If you can find the same part number and the donor car from the breaker yard is also a V40 (with the rear wiper option enabled), then yes, it will work as it is. Also, if it helps, I have a few refurbished CEMs, so I can send you one to fit one your car and you can then send me back your old one. This way, you can keep the car on the road. If you want to make 100% sure that the CEM is at fault, you can remove the bulb and measure the voltage on the bulb holder. If you are getting 0V, then it is 100% the relay in the CEM
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