Strange battery issues TDCI 1800.

[Soapy66]

Hi all, drove home from work this morning 30 miles with no issues, no warning lights after leaving the car for 8 hours. Went to bed, 10 minutes later the alarm kept going off along with the Wiper Blades operating. Car was locked, missus could not get the fob to work, so she left it and went to off work, managed to wake up and get in the car, just a load of clicks and the display went off, thought dodgy battery so I bumped it, ran ok, steering fault came up, then cleared, it now runs and starts ok, my test lamp says battery is ok and it is charging. Alternator is providing 14.5V.

But after turning the engine off, the seat belt unclipped alarm sounds, the wipers drag very slowly across the screen, the indicators flicker, turn the key to ignition and all is calm, the engine will start and run. Assumed a faulty battery so took the one off my diesel Landrover and the fault was the same. This battery was showing 12.2V so I thought it needed charging, was left charging all day. Now at nearly 13V.

Reconnected it, all seemed well, but the alarm has just gone off and the wipers are slowly going across the screen again until the ignition is switched on.

I can hear what sounds like relays in the engine bay click on and off and under the passenger foot well intermittently.

When this is going on the multimeter is drawing between 3 and 7 Amps.

With the ignition on, the draw is 7.1 Amps after the glow plugs have fired up.

I am stumped, any one any ideas please?

Regards

Paul.

[pragmatix]

Likely to be corrosion on the back of the fuse box or its connections a clean up should do the trick not hard but time consuming.

[Soapy66]

Ok, interesting, thank you for replying.

Regards

Paul.

 

[isetta]

If it’s same as 2008 mk2.5 then fuse box is above front passengers feet. On the one I worked on it looks like a fuse box with loads of cable plugs on it but when removed from car I took it apart and found a circuit board inside with computer chips etc on it. I would imagine if damp got in there it would cause havok. Everything in car other than engine is controlled by this

[Soapy66]

Ok Isetta, it is under the passenger seat, I will try and have a look, work permitting, no access to a garage, light and warmth, so al done on the drive.

Been thinking though, if it is a corrosion problem, why does it only show up when the ignition is off?

Regards

Paul.

[Tdci-Peter]

On 11/27/2019 at 5:27 PM, Soapy66 said:

10 minutes later the alarm kept going off along with the wiper blades operating. Car was locked, missus could not get the fob to work,

Wipers, Indicators, Intruder alarm, Locking are all controlled by the BCM / GEM / Passenger fusebox. These are all names for the fusebox under the glovebox. As well as fuses and relays, it has a complex processor module that controls most body related functions.

The steering light is an exception, but this may be a result of the bump start.

The seatbelt system has its own module, but the belt alarm must go via the BCM, because on my car putting an indicator on silences the alarm.

So if you have eliminated low voltage from the battery, it almost has to be a fault in the BCM, most likely damp or corrosion. This is quite common.

(I assume the 7.1A with ignition on was after the glowplugs had timed out, they should draw 30A to 60A if working properly.)

Best course of action is to unplug and remove the BCM, leave it in a warm, dry place (airing cupboard), and ideally strip the covers off to inspect and clean it, though a good drying may cure it at least for a while.

There are possible routes where ignition off can cause these problems in such a complex module. Most of the switches, including wiper switches, are earthed on one side, and go to the BCM on the other side. A partial short from a switch track on the pcb to a track normally powered up by the ignition will make the switch appear to be closed when the ignition goes off. There are lots of ignition powered tracks on the pcb, so it is not too unlikely.