Help with fault code

[Isthatacaddy?]

Hi all, looking for some assistance if possible. I tried to post in the electrical section of forum but don’t have permission.
Using an OBD scan tool I keep getting an 01598 drive battery fault code and my radiator fan seems to constantly run, not long after starting. It stops when I turn my ignition off. The idle raises to 1000 rpm as soon as the fan kicks in. I have cleaned up various grounding points below the battery box tray.
Battery is not very old 12.65 when off the vehicle. 12.56 v when connected to vehicle. 13.8 volts with the engine running, if this is relevant.
If I measure between the alternator casing and the battery - terminal my fluke multimeter shows -0.803M ohms
2009 1.9 tdi
I have another caddy 2.0 tdi 2016, this measures 0.2 ohms between the same two points.

Anybody offer any help/assistance please?

[PeterAFox]

I know on mine the fan runs if the sensor in the front bumper (if I remember correctly, the air pressure sensor) is disconnected. If you stick your head underneath you should be able to see the cables for the lights and also a wire-pair for the sensor (just to the right of centre when you look at the car from the front). Check if these wires have been damaged or disconnected / trace them back and look for damage.

With your low voltage fault, I would first:
- charge the battery up
- disconnect the main cable on the alternator
- fix a plastic bag over the end of the cable to insulate it, maybe tie it to something so it doesn't get caught up in anything
- connect the VCDS or whatever, start the engine, read and save codes, and then clear them
- Read out fault codes again

If fault doesn't reappear, it could be your alternator regulator.
If not, post again.

[Isthatacaddy?]

Cheers Peter, I will give that a try. Am I right in thinking that this thick black cable is what puts the charge back into the battery? What do the other two cables on the connector do?

[Isthatacaddy?]

I disconnected the thick black wire on the alternator, rescanned it and it came up with glow plug cylinder 1 open circuit. Cleared fault code using OBD eleven, reconnected the black alternator cable, rescanned it and it came up with the same fault code. The glow plugs were all replaced quite recently.

[PeterAFox]

Has your 01598 fault gone? And the fan now behaving itself? I meant you should run it before reconnecting alternator cable after clearing faults.

Glow plugs: swap 1 and 2 to see if fault moves, if it doesn't then probably wiring

[Isthatacaddy?]

With the black cable to alternator disconnected, the 01598 code doesn’t pop up and the fans didn’t run. Let the engine run for about a minute. Reconnected alternator and restarted and rescanned. 01598 reappeared and the fans kicked in and the idle raised to 1000rpm. The fans ran for about a minute then turned back off and the idle dropped back down to normal. This is with a cold engine.

I also swapped cylinder 1 and 2 glow plugs and the fault shifted to the next cylinder, so it looks like I need one of them at least. I am starting to think it might be a wiring issue and a bit of dampness with all of the rain lately and it hasn’t been getting used much of late. I have previously repaired a wire in the loom in front of the gearbox so I will have to have another good look in there when I get a chance. There’s maybe a bit of chafing going on. Not enough to cause a fuse to blow as I have checked them all.
Thanks for your help and advice.

[PeterAFox]

A few very experienced engineers strongly advised me to always change all four glow plugs at a time......