P38 BECM Wont stay asleep.

Hello there.

I know this question had come up before, and believe me I have read a lot about this over the last few months.

Thing is now I am stuck for what to do.

I have a 1995 Range Rover SE 4.0 with a manual gearbox, no sunroof.

A while ago the battery went flat, so I replaced it. Then a few months later it went flat again. So I started trawling arounf looking for causes. The first and most glaring possible problem wwas the RF unit and the 433mHz frequency. I thought bingo, I have cracked it, must be the PIR triggered outside light right next to the car. So disconnected the window aerial and hey presto, a few worry free weeks of motoring. Since then the car has been parked away from the lamp at the other side of the house. Then a few days ago I went to get in the car and I couldnt blip the central locking even from inches away from where the sensor is concealed. Manually unlocking the doors, I found that everything was completely dead. After trying to charge battery and jump start car from a donor, still no luck, mainly due to lockout and battery wouldnt stay charged long enough to enter emergency code. So battery off car and on charge for a day on trickle. Sure enough this was enough to unlock code, start it and get it moving. So after reading another forum thread I put multimeter in line with negative lead and found that on locking the car the current settled at 0.54A. After a minute or so dropped gradually to 30mA (As the BECM went to sleep). After exactly 3 minutes the current went back up to 0.55A for exactly 2 minutes, the dropped again steadily to 30mA. This cycle repeated everytime. Even got to point I was counting it down from 10. I did the same test without locking the car with same result apart from I am sure first sleep cycle lasted 4 minutes, but I could have mis-timed it.

So to recap,

0.54A drops to..
30mA for 3 minutes
Rises suddenly to
0.54A for 2 minutes
Over a few seconds drops to
30mA for 3 minutes
...and so on.

Pretty sure its not RF based interference, what could possibly be causing this to such a specific time frame.

I really would appreciate any assistance anyone can provide

Many thanks in advance

Tim

Why are you sure it's not RF interferance? You already know the receiver is susceptable to interferance. The RF receiver can also fail internally which will give your problem.
A PIR triggered outside light should not emit RF so that is unlikely to be the cause of your original problem. WiFi, wireless door bells, Owl electricity monitors etc are the usual culprits.

Thank you for such a quick response.

I am not 100% sure, but from what I have read on the RF issue the times didnt seem so distinct. I was not aware that they broke, just were not very good. If someone could tell me for sure that it was that part I would just change it out for a new one. Perhaps if I could borrow a signal detector I could maybe see if there are any being transmitted.

Do a search. Plenty of threads on duff RF receivers flattening batteries, burning out door locks and locking out the BECM not just from stray RF signals. The internals fail causing it to repeatedly signal the BECM. You won't find that with a signal detector. you can try disconnecting the connector with 3 wires as well as the blue aerial wire, that will stop the interferance but may cause you other problems.

Will do, not sure I like the idea of disconnecting it if it may cause more problems. I suppose if I do it and then do sleep test straight away I can then re-connect it either way.

It looks like an expensive part, but a lot more robust than leaving aerial disconnected forever with a solar panal on the dash.

At least now I know what I am doing should take long and there are a couple of reasonable independant parts dealers around me that are very helpful.

with the RF receiver completely disconected will the Becm go to sleep? mine has a steady current draw of .5A that never drops below that. i have disconnected the power wire to RF receiver but will try completely unplugging it if this will help. will i be able to lock/unlock the car with it out?

aniesigh said:

with the RF receiver completely disconected will the Becm go to sleep? mine has a steady current draw of .5A that never drops below that. i have disconnected the power wire to RF receiver but will try completely unplugging it if this will help. will i be able to lock/unlock the car with it out?

Click to expand...

Sounds to me like your becm isnt going to sleep. You must have a heavy duty battery or mine is just inferior, surprised yours hasnt gone flat.

Anyone else got any ideas or shall I take car into middle of nowhere and see what happens there, if it sleeps longer.