SwedeSpeed - Volvo Performance Forum banner

1 - 10 of 10 Posts

·
Registered
Joined
·
6 Posts
Discussion Starter · #1 ·
hi people

i been struggling the last couple of days to get my xc90 running, the past couple of weeks my mrs has been driving and the battery light has appeared and gone away so i just thought it could be just the battery going as its winter now and shes been using the heated seat.

well got a call the other day car battery died she needed a jump start, got her jumped and started straigh away.

it was getting late so i thought i just buy a battery and return it if its not the case, well got back home after buying the battery i tested the alternator with a multimeter, it was working so i changed the battery.

started it again then voltage started getting high 16v then dropped to 12v, so i thought it was the regulator so i checked it and removed it. the brushes seem pretty warn one being very low, so i thought this was the cause of the high low voltage so i ordered a new one.

i installed the new regulator i ordered from ebay guess what didn't work at first so i run it and it started working pumping out 14v and above to 15v,after a drive the red lights back on checked the voltage its dropped down again to 12v. im lost what to do now im just thinking it could be the alternator or a faulty cable any ideas.

I have a dice but im new to it and unsure if there is anyway of diagnose it through it??? also the aux belt seems pretty tight and alternator is turning well.

can anyone help.. thanks
 

·
Registered
Joined
·
3,135 Posts
No signature, no description of MY plus Engine. Can't help without some level of detail.
 

·
Registered
Joined
·
3,135 Posts
So, if you have VIDA, you know this fault is from the CEM (Central Electronics Module).
CEM-1C02, Signal too low: “Diagnostic trouble code (DTC) CEM-1C02 is stored if the control module registers that the L signal is low or that the generator (GEN) is not charging.
I’m taking a guess in that the CEM thinks the signal is missing (too low usually means it’s not there). You ought to be able to validate this in DICE/VIDA (don’t have it up right now, maybe Network Communication/CEM, something like that) and you ought to be able to see voltage readings from the regulator tap. You can also see in the Fault Section the number of times it's been reporting a fault in however many drive cycles. I know you mentioned that you were getting voltage readings, was that from VIDA or from a multimeter?

First step in the VIDA troubleshooting is note to check the integrity of the signal cable electrical connection between alternator (generator) and CEM:
Checking the signal cable
-Ignition off
1. Disconnect the 20-pin connector (group A) from the central electronic module (CEM)
2. Disconnect the 1-pin connector from the generator (GEN) (1B).
3. Check the signal cable between the central electronic module (CEM) terminal #5A and generator (GEN) terminal #1B (the red / white cable with flat pin). Check for a short-circuit to ground. [or an open]

If cable is okay, then VIDA suggests you need to replace the regulator (know you already did). So question, is the one you got new and is it PN 8637851? I’m going to waffle a little as you said you saw some pretty big swings in voltage. But VIDA is not reporting a high signal, it’s reporting a low signal. Could be the regulator is not working properly but you’ve already gone to the trouble or replacing it and nothing changed. But it’s the next step per VIDA.

But if this all does not work, you might be thinking about giving the CEM a good inspection. That’ll happen by default when you take the connector off the CEM to check the cable continuity but since you’re a 2004, there have been water issues with the plenum right above the CEM and they can leak under specific circumstances. I’m hoping that your problem is a wire or a regulator as if it’s water ingress on the CEM, that’s a whole ‘nother can of worms. Can be fixed (removed and cleaned), can be replaced (Xemodex does them). And if the plenum is the problem, there are a few remedies for that (OEM re-fit kit, DIY with silicone).

Hope this help and for sure let us know what you find out.
 

·
Registered
Joined
·
6 Posts
Discussion Starter · #5 ·
I've had a little chance to look at the car I removed and reinstalled the regulator it seems to have power running out of the alternator also to the battery, I checked this with a multimeter but unsure if it's right. The voltage raises and drops 14 to 15v would this be because the cem ecu is telling the regulator to do this? I've attached a picture of the read our from the ecu and the ecu reads low voltage, I'm lost I need to check my multimeter is working ok cos something don't add up. If I remove the signal wire from the regulator Red white wire should the regulator stop putting out?

I pulled out the cem couldn't find any damp but didn't have time to test anything, I do seem to have a wet patch on the passenger side on the carpet, but I have a rhd and the cem is on the right.

Thanks j
 

·
Registered
Joined
·
3,135 Posts
Found this on a Volvo internal presentation (New Car Features 0420):
Within the alternator [assume this is within the regulator] is a control module (ACM =Alternator Control Module) which is controlled by the CEM via a LIN bus. The CEM calculates appropriate charging voltage from the temperature of the battery. Included in the calculation are parameters such as outside temperature and running time ("radiant heat from the exhaust system"). As before, the alternator starts to supply current a couple of seconds after the engine has been started, following which the charging is increased to the level required.

If there is no communication with the ACM:
After starting the alternator first charges at an engine speed of approx. 2100 rpm. In addition, the charging does not follow a charging curve but the alternator provides either 0% or 100% of its capacity. Fault tracing on the ACM and the communication with the CEM can be performed with VADIS via the CEM. The ACM can be replaced separately, a software download is not required after replacement.

Since you have VIDA, see also Product Specifications/Design and Function/3 Electrical System/32 Alternator and Regulator/Generator(GEN)/Design or Function or System Overview. That'll give you more detail than maybe you even want to know.

I'm still guessing between the code and what you're noting, CEM to ACM interaction is not working or something is wrong with your regulator. Now comes the question as to why.

Hopefully someone who has experience with this same scenario can comment further.

Should have figured this was a RHD vehicle. Still, glad the CEM is not damaged but if you have dampness on the passenger side, would be good to pull the A-pillar cover and make sure you're not having a sunroof drain issue (assuming you have a sunroof).

Good luck !
 

·
Registered
Joined
·
6 Posts
Discussion Starter · #9 ·
I applicate the help I have brought a cheap replacement regulator, I think I will have to buy a bosch oem part. I will update you soon thanks a lot
 
1 - 10 of 10 Posts
Top