Land Rover Repair: BeCM electrical fault affects dash, power relays, ground faults

Question
QUESTION: My electrical system in malfunctioning. I recently had a used becm unit put in my car and had the car recallibrated, new battery, transfer case, and air bags for the suspension. My system seems to work fine now but every now and then my gauge will be on the fritz and the system reads electrical fault, fuel gage fault, gas fault, etc. My driver seat is constantly blowing its fuse. When the system indicates a fault which may just pop up and go back to normal or stay lit for a minute it seems that if I readjust myself in my seat the indicators go back to working normally. I have had a mechanic check my wiring and even unplug my driver seat so that it wont keep blowing the fuse. My original becm was fried due to the electrical. Could my driver seat be the problem? What could be the issue and resolution?

ANSWER: Hi 99Rangie,

certainly sounds like one of your seat motors could be the root cause of your electrical problems.  

Did you check the seat power relays under the seat?

SEAT POWER RELAY
Service repair no - 78.70.47

NOTE: 2 power relays are fitted to electrically operated seats without
position memory function.

Remove
1. If possible, raise seat cushion to full extent to improve access to relays.
2. Remove relay from connector block.
Refit
3. Reverse removal procedure.

You have a motors for Rise/Fall, recline, tilt, headrest motor and then there are
the heating elements.  So, there are quite a few possible connections to examine and test for ground faults.  

Here is website that has information, instructions, photos to help you diagnose electrical problems for your Range Rover:  http://rangerovers.net/repairdetails/index.html#bodyelec2

Best of luck,
JohnMc

---------- FOLLOW-UP ----------

QUESTION: So my seat motor can cause an electrical fault which can cause all indicators on the dashboard to malfuntion?

ANSWER: Hi 99Rangie,

short answer:  yes.

Here's some info from the workshop manual:

The seat heater function is controlled by switches on the HEVAC ECU control panel. Each switch when pressed, completes an earth path which is sensed by the BeCM as a seat heater request and activates the appropriate seat heater. The seat heaters only operate with the ignition in position II and the engine running.

The electric seat operation is controlled by the BeCM via the seat outstations. The BeCM receives input information from the outstations for the selected functions. It then outputs the appropriate command signals, via the serial data bus, to the applicable outstation, which then operates the selected function.

(Did you know that) the BeCM has its own integral fusebox containing 22 fuses. The fuses are accessible via an access panel located on the side of the front RH seat trim panel. Each fuse protects one or more electrical functions controlled by the BeCM.

The link to the dashboard (instrument pack) is via the BeCM:

Fuse# - Rating - Function

1 - 10A - Instrument pack, Clock, Radio, Centre console switch pack

7 - 10A - Up to 99MY: Airbag. From 99MY: EAT ECU Ignition supply, Transfer box ECU ignition supply

8 - 30A - Car phone, radio, front cigar lighter, HEVAC. Up to 99MY: Aerial amplifier

10 -30A-  RH seat Battery 1, RH seat battery 2, RH seat lumbar, Rear cushion battery 1, Fore/aft adjustment battery 1, Front cushion battery 2, backrest battery 2, headrest battery 2

20 -30A- LH seat battery 1, LH seat battery 2, LH seat lumbar, Rear cushion battery 1, Fore/aft adjustment battery 1, Backrest battery 2, Front cushion battery 2, Headrest battery 2

It's possible that a problem within the BeCM can jeopardize the interface with other components and I've seen it on my Disco.  Radio short caused dashboard light failure, taildoor defrost element short caused same dashboard outage.  It's weird but logical, for Lucas electricals. :)

Now, I'm not saying that this IS the cause but I am suggesting it could be.  Check out the BeCM fuses mentioned here to see if there is a short, otherwise, you'll have to use a multimeter and start looking for the short...a slow process indeed.  

Best of luck,
JohnMc

---------- FOLLOW-UP ----------

QUESTION: If there is a short which has to be in the 20-30A, what do I do to resolve the issue? Do I replace the driver seat, driver seat motor?

Answer
Hi 99Rangie,

good question.  Is it cheaper to disassemble the seat, trace back from the relay to determine if a wire, connector harness or motor is shorted OR would it be easier to just swap in another seat.  If seats were readily available and the price was right, I'd try the seat swap.  Too bad you don't know someone with a '99 Rangie who who let you swap out the seat.  MAYBE your mechanic has access to a Rangie seat and would be willing to temporarily swap in a seat to see if it solves the problem?  Worth a try and you've already (I sure) paid them handsomely for the work they've done in trying to solve this.  They should be willing to try.

I'd go with a temp seat swap - if possible - and if it works, keep the seat.  IF it does not, you could have other electrical woes in conjunction with the seat electrics.  ouch. These electrical problems are very mercurial and it may take time to solve.

Best of luck,
JohnMc