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AndyC the WB
| | Posted on Saturday, November 09, 2002 - 02:57 pm: | 
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OK, here's an interesting challenge for those of you who are up on electrics. I have a P38A rangie which is draining the battery. With an ammeter in the negative lead of the battery, I can see a current draw of 0.6A for two minutes exactly, which then drops to 0.06A or lower for up to 30 seconds, and then returns to the higher value.
I have checked the alternator is charging the battery, and removed the radio and after market cellphone hands free kit. I have been able to reproduce this with the alarm active, inactive, doors open (slightly higher draw due to seat outstations being powered), doors closed, bonnet open, bonnet closed. Never has the fault failed to appear.
I take it to an independent LR specialist, and current draw falls to 0.06A or lower two minutes after power off. In other words, the fault doesn't happen. The only thing different is that they have a different ammeter, the car is 10 miles from here, and the car is level in their car park, while my drive slopes slightly (tried with the car both ways around - same things happens).
I have tried removing every single fuse and relay in both the engine and BeCM fuse boxes and the behaviour remains the same.
Two questions:
1) Does anyone know anything I can try to get to the bottom of this?
2) Am I going to cause problems if I disconnect everything from the BeCM and reconnect things one at a time to see when the problem recurrs? |
Jason Vance (Jason)
| | Posted on Saturday, November 09, 2002 - 03:55 pm: |
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What year is the RR (+ FI or carbed)?
Pretty simple, as another member of this board has pointed out and tested, pull the positive lead off of the battery and test for continuity (use the ohmmeter function to measure resistance) between the disconnected positive lead and the negative lead on the battery.
Here's what you are looking for and why: you want to find a very high resistance value. Because there are still components that use electricity while the engine/ignition is off (clock, engine ECU is FI, your cell-phone battery source if not connected to a switchable source), they are part of a closed circuit completing the positive to negative connection with the device functioning as a resistor of sort. The high resistance means exactly that...voltage is moving across because the device is still functioning, but not much.
If you get a very low resistance value, this means that there are potentially many more closed circuits pulling more voltage (completing paths of "less resistance"). First, hunt out any closed switches (like from open doors, or the open hood if there is an under-hood bulb) and rule out whether the circuits become open when the doors/hood are shut; there should be a sharp increase in resistance when the circuit goes from closed to open.
Anyway, probably time to invite over a friend and a case of good beer...it's going to take some time checking all of the possible circuits/relays that may be contributing to the battery drain.
You don't have an auto-dimming mechanism on the interior lights...those stay on for about 2 minutes when the doors are left open (e.g. if you have these and a switch at any door is broken and stuck in a closed-circuit position, the interior lights will shut off after about 2 minutes -or more- ). Hope this helps, even in the slightest. |
AndyC the WB
| | Posted on Sunday, November 10, 2002 - 10:45 am: |
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Jason
Thanks for the advice, but I think you are talking about a classic rangie. The P38A has far too much electronics on board.
The "proper" troubleshooting approach has taken me about 10 hours over several weeks to get nowhere, and I tried something today on a bit of a whim.
It turns out that the receiver for the alarm remote was sending a spurious signal and waking up the BeCM. |
Jason Vance (Jason)
| | Posted on Sunday, November 10, 2002 - 11:33 am: |
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"far too much electronics..."
Sorry, it doesn't matter if it's a Classic or a new one. Electronics are just a bunch of circuits; just 'cuz there are more doesn't change things. If anything, the newer vehicles that compartmentalize many sub-components may be easier to tease out (e.g. disconnect window ECU; disconnect seat ECU, etc.).
The only easy solution is a good guess...in your case, it looks like you found it. |
AndyC the WB
| | Posted on Wednesday, November 13, 2002 - 02:15 pm: |
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Well, I'm kind of tongue in cheek here. I can work out the electronics better than that oily thing under the bonnet :-)] |
Jason Vance (Jason)
| | Posted on Wednesday, November 13, 2002 - 02:36 pm: |
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I can also push my Rover faster than that oily thing under the bonnet.
LOL! |
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