Engine: D5: B+ cable replacement

[wingers]

I've been trying to resolve an electrical issue which has thrown up the Power System Service Urgent light on the dash.

The alternator charging voltage is low at 13.3V (measured at battery) but everything seems to work correctly despite that - I guess it's still charging sufficiently if not fully.
The car has had a lazy cranking speed for some time so I suspect that is just the consequence.

I've checked a number of voltages and the main voltage drop is between alternator B+ and the fuse box. This has about 0.25V drop at idle with AC/screen heaters etc on full. There is also a 0.1V drop from the fuse box to the battery in the boot. The voltage measured between alternator body and alternator B+ is 13.7 which seems ok.

I've so far changed:
1) Alternator regulator for new eBay one
2) Whole alternator for Bosch unit (inc another new regulator)
3) The battery for a new Yuasa one

None of that has got rid of the problem so I think the cables are next to hit but I can't find anywhere to buy them. Does anyone know where they can be sourced? I can try Volvo direct but I suspect the price will be painful, and I probably can't get through to them until Monday so thought I'd ask on here first.
Is it worth changing the whole glow plug, alternator, starter loom, or just adding a new live cable on top?

Or if there is anything else that's worth checking first please let me know...

Cheers,

Wingers

[VOLVOBOY]

Hi.
I don`t think your numbers are too far off , to be honest.
I`m assuming 13.7 Volts on a warm/hot engine .
I would expect to see something over 14 Volts at the battery after a cold start and for this to decrease as the engine warms.
You could try disconnecting the battery and resistance testing the cables . I think this is poor earths and most likely at the engine. There is the main cable which is bolted to the engine block near the starter motor and runs to the chassis behind the nearside headlamp.This is a classic for corrosion and bad conductivity. It really needs to be removed , check the crimps have not corroded , cleaned and re-fitted. It is a sod to get to. There is also a smaller cable from the cylinder head (near the brake servo) to chassis.
The small wire from the alternator ( red/white on pre-facelift , green/white on post facelift ) runs to the CEM. This is the signal / trigger wire that makes the alternator start charging when the engine is started. I don`t think there`s a problem with this as you have charging at the battery. But this wire runs to connector 54/3 on the back of the CEM. On post facelift cars this is an area prone to water ingress and oxidation on connector pins. It is an area well worth checking against water incursion. Once water gets into the CEM it has been the death of many perfectly good cars.

[SwissXC90]

14.4V is the proper charge voltage when the engine is running and over idle speed.

[XC70Virgin]

Have you checked your battery to eliminate it from the issue?

[SwissXC90]

And I would focus on the ground connections: battery to chassis, and engine to chassis.

Also, ensure the main B+ cable connectors are clean and tight on starter motor, battery, and any joints in between.

Bit fat cables like the B+ cable do not fail
It is much more likely that the ground straps are corroded, or the terminals are corroded.

[wingers]

Thanks for the replies.

The ground side has <0.1V drop from alternator to battery so I don't think that's causing a problem in this case.

I fitted a new battery to check that and it didn't help.
I haven't been able to get any further with finding new positive cables so will speak to Volvo dealer tmrw I guess.
I did take them off and clean up the spade terminals but it didn't help. The only other thing I found is that the crimps between cable and spades are getting hot when running so I think that must be where the resistance is. I might try as a last resort to strip back the end of the cable and solder over the crimp. It would need resleeving but might be enough to get the voltage up above the point the dash light comes on?

Wingers

[VOLVOBOY]

Hi.
You should be measuring Ohms Resistance and not Voltage.
If you do this first and find low Resistance , which you want , you`d be wasting your money buying replacement cables.
The fact that you have cables getting hot tells you there is resistance. I don`t think you`d be able to apply solder because you`d need some serious heat. The cables really need re-crimping .
My advise is to get hold of cables from a salvage. You can check the cables before fitting, return them if they`re rubbish or repair before fitting.
I think this will fix the lazy Starter Motor.

[R-P]

Seconded: heat means resistance in this case. And soldering won't work unless you have a gasflame and even than it will be hard.
But ohms are hard to measure when it is probably far under 1 ohm.

If you can get hold of a regulated powersupply where you can limit and control the current, then is is possible to take the beginning of a cable and the end and run a known current through it, e.g. 1 ampere (1000mA).
If e.g. the cable from the alternator to the jump-point under the bonnet than has a voltagedrop of 5mV, but the one from the jumppoint to the battery in the back has a 50mV drop, then you know the second part and particularly the ringterminals are suspect.
5mV drop would mean a drop of half a volt at 100A (startercurrent is higher, but lets stick with easy numbers for easy math), which is on the high side but acceptable (35mm^2 cable (which my Volvo startercable is I think) should have a resistance of about 0.5 milliohm per meter, so 0.5mV to 1mA at the 1 ampere we measured at (assuming it is between 1 and 2 meters), but the ringterminals will ad a little resistance).
But the cable from the jumppoint to the battery, lets say 5 meters, should be (5x0.5ohm=) 2.5milliohm. So the voltagedrop should be 2.5mV plus the same kind of voltagedrop from the connectors like from the first cable, so certainly under 7.5mV in total. 50mV means there is definitely something wrong in that cable.

Here's a pic of the engine-to-chassis cable of my Volvo... found after intermittend powerissues. It pulled right out. And this didn't only happen to me, so check all crimped connections, especially the 'hot' ones.


I'm reusing this cable elsewhere (solar powered 12V-to-230V powersupply in a grid-less garage) and replaced it with a 50mm^2 cable I crimped myself (have the tool for it). I wanted to replace the startercable too with 70mm^2, but there's too much issues that are more important than putting in some better cable for 1500W in amplifiers...

[wingers]

I double checked this on a cold start and got 13.7V at the alternator, 13.5V at the battery.
This is with headlights but no heater. When I put on full AC the battery voltage dropped a further 0.4V.

That means I'm never getting more than 13.7V from the alternator. Based on the comments above that seems low?

Regarding the cables, I tried Volvo who apparently don't stock the positive cable anymore. They did say they had the starter motor one but its only available as a full engine harness, so I didn't even ask for a price on that

I think the next steps are to either take it to a garage or to get hold of a vida kit and see what the car thinks is wrong?

Wingers

[wingers]

So I got hold of a vida kit (from cheshired5 on here) which seems great.

The codes its got related to the battery/alternator are
CEM-DD21 LIN-bus 2 signal missing
CEM-DD30 Communication with ACM module signal missing

I cleared the codes and having run the engine again the same warning comes up on the dash but now the above fault codes don't reappear. The only ones showing are related to other things (audio system mostly).

So it seems there is (was) an issue with alternator control but has that now been fixed?
The Lin signal wire is connected so I'm not sure why that's not getting through. A quick dc voltage check on that gives 11V when the car is idling.

Has anyone else had those codes come up before and found a fix, baring in mind its a brand new alternator & regulator?

Why would there be no fault codes if the dash is still complaining of an issue?

Regards,

Wingers