Other 70 Problem: Intermittent electrical fault

[Stu Brown]

For about 8 weeks I have had an intermittent fault where the battery discharges within about 8 to 10 hours after switch-off. After the first occasion I replaced the battery and all was fine until the same thing happened a week later. I noticed that a tell-tale sign of the problem was that the radio stayed on when the ignition key was removed, and the problem persists for between 1 and 3 days. The next time the problem occurred I waited 1 hour and measured the current drain at around 5 Amps. The car has been into the main dealer twice for diagnostic checks but, annoyingly, on both occasions the problem had cleared by the time I had got the car there and all was declared to be OK. The problem re-occurred yesterday and I had to disconnect the battery to avoid getting stranded.
I have noticed that these incidents always occur during periods of high humidity (rain + temperature fluctuations), and suspect that moisture is wicking its way in or condensation is forming somewhere inside a connector and making the ECU misbehave. Has anyone else had a similar problem?

I should add that the vehicle is a V70 D5. Registered Feb 2006.

[Jim314]

Could it possibly be a problem with the ignition switch? How and where did you measure the current drain? A 5 A drain is consistent with the discharge time of 8 to 10 h.

My battery drained over a period of a few days and I attributed it to the alarm siren battery being bad and constantly demanding recharging. I pulled fuse #38 in the panel at the end of the dash and have not had a recurrence.

[grass hopper]

could be moisture/rain dripping onto the CEM,it leaks in through a panel close to the wiper linkage,there was a modified sealing kit if it has not already been done,worth asking the dealer to check for signs of water ingress in that area.

[Stu Brown]

The main dealer declared that the ignition switch was OK. I measured the current drain using an ammeter clipped to the main earth lead on the battery and touching the battery post as I lifted the earth lead off the battery. Is there an easier way to do it without disconnecting the main lead?
I'll look at fuse #38 next time. Have you just left it out permanently?
Thanks for your input.

[Stu Brown]

Thanks Grass Hopper. This car had a bit of a brainstorm in 2008 due to water ingress. The dealer changed a module (maybe the CEM) under warranty. Maybe they didn't fit the modified sealing kit. I'll take a closer look.

[Missing Lincs]

A useful way to measure current for individual circuits is to measure across the fuseholder. I bought an adaptor which plugs in instead of the fuse, the fuse then plugs into the adaptor to maintain circuit protection and your meter connects across the adaptor - sounds more complicated than it is!
What you've measured is good to show that there is a current drain but you really need to be looking for the source. As everything goes through a fuse at some point on these cars its a good point to do measurements, even if it is a pain going through all three fuseboards.

[Jim314]

Originally Posted by Stu Brown

The main dealer declared that the ignition switch was OK. I measured the current drain using an ammeter clipped to the main earth lead on the battery and touching the battery post as I lifted the earth lead off the battery. Is there an easier way to do it without disconnecting the main lead?
I'll look at fuse #38 next time. Have you just left it out permanently?
Thanks for your input.

Yes I have permanently left out fuse #38 ('alarm') in the panel at the end of the dash. My alarm doesn't work anyway.

The device to measure the current through each fuse sounds very useful.

To measure the total current I assume one would use an inductively coupled ammeter probe at one of the cables at the battery. That way one doesn't have to undo the connection of the battery. Of course, this gives the total current in all the circuits. To identify the exact circuit with the drain one would have to begin pulling fuses or use the device referred to above.

[Stu Brown]

Thanks Jim & Grasshopper for advice so far. I don't have a fuse #38 at the end of the dash. Different specification I suppose. Yesterday I spent some time checking the effect of pulling out each fuse. It took me a while to realize that each time I opened a door or the tailgate some electronic circuitry is activated for a while (until door closes or it just times out). Anyway, in a nutshell, I found that Fuse 10 (audio) and fuse 11 (amplifier) were causing a residual drain of 2.43A with the radio OFF! With these two fuses removed the residual drain drops to about 0.01A with the car locked and immobilised. At the moment, therefore, I have no entertainment in the car - also there is no audio output from the reversing sensors.
Before I ask the dealer to check the audio system, do you think there is a possibility that the reversing sensors could be the root of the fault? Also, can you tell me where to get the adaptor you mentioned that goes into the fuse holder?

[bic1]

Hi, the Ammeter you are looking for is available from Maplin.

[Jim314]

If you pull a fuse and the fuse is intact, then you know you have no current in the circuit above the limit of the fuse. So you could just read the current in the circuit by putting the ammeter contacts in place of the fuse, assuming your ammeter will read that high. I have a 40-year-old dial multimeter that only reads up to 0.6 A DC so I can't test my circuits with it.