Hi all! Sorry for all the detail, but I've got a 2002 XK8 convertible with a ~220mA parasitic draw that I can't seem to track down or eliminate. I've done a fair amount of trial and error but can't seem to isolate.

So far, I have determined that if I pull fuse #5 on the driver's / LH side (US car), which is indicated as the "[b]ody processor module logic supply", it will drop to ~40mA within a few minutes of doors and boot being closed. I pulled many other things (remainder of the driver's side fuses, all the passenger side fuses, all the boot fuses while keeping #5 in and it still seems to maintain this draw for up to 5+ hours, long after I'd expect it to sleep.

Pulled both fuse box connectors under the bonnet, no apparent change. I pulled the boot relays (in the fuse box, in the T-shape, without re-pulling fuses) in the boot, no apparent change. I'd have disconnected the main supply but I'll admit I couldn't figure out how to easily get the red-capped connector off.

Removed the glove box and pulled the harness off the BCM; draw goes down to ~10mA within a couple minutes of closing everything. I swapped out with a different BCM (with that of another '02 XK8 Convertible with a VIN <1000 away - couldn't find anyone who actually recorded VCATS suffix on parts =/ ). No change, so probably not the BCM itself.

I disconnected the main three SCM connectors (but not what appears to be the antenna connector) under the boot fuse box, that only got it down to about ~210mA, so that didn't help.

I made sure the ignition flap seemed to be closing and lubricated it maybe 5 times, I'm reasonably confident it's not stuck open. I made sure the steering wheel selector was NOT set to auto, have headlights fully off, wipers fully off, turned off both heater and radio before disconnecting battery, nothing plugged into cigarette lighter port.

Touched the battery cables together to try to get it to hard reset the components.

I feel like something is keeping the BCM awake but I can't seem to figure out what. Can I stick multimeter leads into some of the harness pin receptacles to see what is keeping it on or something?


The only thing I can think of that might be related was in the notes from the PO from prior to my ownership, which stated:
"Tech tested and found interlock functioning but no power coming to interlock.
Tech notes power/signals run through ecm, gear selector illum module, instrument cluster to the interlock control and out to the solenoid.
Tech suggests attempt brake switch to rule out before continued pin testing of modules.
Tech does note code u1261 scp (-) circuit failure is present and could be caused by the battery (which does test low), instrument cluster failure or wiring.
Tech does note that other issues are present that tie into the scp circuit including the seat issues.
Tech seeing this issue in the past, instrument cluster (no longer available) customer would have to try and source new or used from internet.
Tech disassembled shift assy, removed interlock solenoid and piston, taped together and tucked back in tunnel. Tech installed zip tie to prevent interlock lever from moving and causing shifter to lock."

Though the issue still presents with fuse #7 removed, which is supposed to feed the shift lock solenoid, so I wouldn't expect that to be involved. With #5 in and BCM attached, front fuse boxes and SCM and driver's side #7 disconnected, it goes to ~200mA. I did replace the battery (more than once) and seat control modules after receiving, by the way.

The shop further said "the last time I dealt with this code I had a bad instrument cluster. That doesn't mean it is bad. If you read the notes, the circuit passes from the switch (that appears to be working in the scanner and not likely bad) through the ECM, gear select module, instrument cluster, interlock control to the solenoid so there's a lot of wiring and testing to rule out.
Or we can remove the interlock itself."...which they did, and which I want to fix, but I don't think I was having this parasitic draw until a couple months ago and I've had the vehicle about a year.

Thanks in advance for any thoughts!

 

Some JLR vehicles have had problems with ECU not shutting down when parked near to mobile phone towers ..one was even fooled by a wireless thermometer . Some have shortened the aerial for the remote control with success. Its the 433Mhz ( or whatever you have in US) thats the problem on some vehicles

 

Given that the shift interlock is a fault, I suppose it wouldn't hurt to try and diagnose why. Assuming everything else is working you don't need to test the wiring from "the ECM, gear select module, instrument cluster, interlock control." because that wiring is the CAN bus and SCP bus - if that wiring was faulty there would be a lot more problems with your car than just the shift interlock.

If your stop lights work with the brake pedal, that leaves the not in park switch to test. Of course this may have nothing to do with your parasitic draw, but you have to start testing somewhere.

 

thermal camera and a breakout box

does scp ever go to sleep?

 

BCM feeds a bit of a haystack of modules any one of which could be the needle you're looking for

I don't really approve of just guessing solutions, but to make an exception here, a common source of drain is the alarm sounder behind the righthand wheel arch liner, beside the headlight. Assuming the re-chargeable battery pack hasn't been changed from the original in the past 20 years, it may well have given up and is causing your drain. It's easily disconnected to prove or disprove.