RangeRovers.net Forum banner

1 - 9 of 9 Posts

·
Registered
1995-2002 Range Rover P38A
Joined
·
33 Posts
Discussion Starter #1
Battery dies over night.....sometimes (charging test completed)

Trying to figure out why the the Rover will have a dead battery at random. Some mornings it starts right up other morning it is dead. Some days after work it starts right up, other days it is dead.

I have:
-disconnected all my "aftermarket" stuff (CB & Lights)
-replaced the battery (I did test the old battery and it tested bad, so I did replace the battery)
-Ran the troubleshooting test (see results below)
-cleaned the grounds up (alternator and battery)


1. Engine off, all accessories on for 30 seconds, then off. What voltage 12.6 (this is low, but the battery was drained that night. This was after charging it for a while)
2. Voltage across battery at idle (no electrical load) 14.5
3. Voltage across battery at 2000rpm (no electrical load) 14.4
4. Voltage across battery at 2000rpm (everything electrical switched on) 14.1
5. Voltage at ALTERNATOR at 2000rpm (everything switched on) 14.28
6. Voltage drop between alternator body and battery negative (YES negative). Measure at max electrical load and 2000rpm .14
7. Voltage drop between alternator positive and battery positive. 2000rpm, max electrical load -.06
8. Check Voltage drop from Battery Negative terminal to 1st groundpoint on vehicle .04
9. Check voltage drop from 1st ground point to block -.07
10. Check voltage drop from Alternator Housing to block 0


I am assuming it is a parasitic drain somewhere.....
Looking for help.
 

·
Registered
1995-2002 Range Rover P38A
Joined
·
1,522 Posts
Re: Battery dies over night.....sometimes (charging test completed)

Also check the BECM goes to sleep. Mine pulls 0.63A then after 3 mins drops to 12mA.
Could be radio interference waking it up. Big problem on UK p38's which operate at 433MHz.
Less of a problem in the States on I think 350MHz.
The usual trick is to disconnect the blue wire on the ariel alarm.
 

·
Premium Member
1995-2002 Range Rover P38A
Joined
·
568 Posts
Re: Battery dies over night.....sometimes (charging test completed)

Mine was all good for first 4 years of ownership then when I moved to a different suburb the battery would go flat every two or three days.....finally decided to disconnect the blue wire as suggested and no problems since........just have to get close to the rear for the key to work.
 

·
Registered
1995-2002 Range Rover P38A
Joined
·
1,522 Posts
Re: Battery dies over night.....sometimes (charging test completed)

I have just recently had problems with my BECM waking up.
It started after I bought a new weather station which I did not realize also operated on 433MHz.
I disconnected the blue wire and it is OK.
 

·
Registered
1995-2002 Range Rover P38A
Joined
·
33 Posts
Discussion Starter #5
Re: Battery dies over night.....sometimes (charging test completed)

I will check the BECM and radio interference. I live in rural area, so I have doubts, but by checking it i can find out for sure!
 

·
Registered
1995-2002 Range Rover P38A
Joined
·
1,522 Posts
Re: Battery dies over night.....sometimes (charging test completed)

Use a clamp on DC ammeter to check the BECM current.
 

·
Registered
1995-2002 Range Rover P38A
Joined
·
33 Posts
Discussion Starter #7
Re: Battery dies over night.....sometimes (charging test completed)

I went to test the amps being pulled tonight and my meter had a blown fuse :(

I did disconnect the blue wire from the antenna to see if that helps...at least until I get some fuses.
 

·
Premium Member
1995-2002 Range Rover P38A
Joined
·
255 Posts
Re: Battery dies over night.....sometimes (charging test completed)

Use a clamp on DC ammeter to check the BECM current.
I was going to say just use the built in amp setting on your multimeter. The current reading will be far more accurate at the levels you should be looking for.
 

·
Registered
1995-2002 Range Rover P38A
Joined
·
1,522 Posts
Re: Battery dies over night.....sometimes (charging test completed)

If you use an ordinary multimeter, you will need to disconnect the battery +ve lead and put it in series. My BECM pulled 630mA when it was awake so you need a multimeter that goes up to at least that or it will blow a fuse.
I bought a DC clamp on meter that is actually made in the States. It is accurate to 1 or 2 mA. You don't need to disturb anything and a useful piece of kit to have.
 
1 - 9 of 9 Posts
Top