Defender 300 TDi immobiliser

[100SRV]

Got caught out last night by the failure of the immobiliser on my 1996 Defender. While waiting to turn right the engine stopped and couldn't be restarted by bumping or key.

It's a 110 station wagon so a heavy thing to get rolling to somewhere safe.

RAC arrived within the hour and we both came to the same conclusion; immobiliser failure.

Presently bypassed with some wires and a fuse, makes the immobiliser a bit irrelevant because starting was so easy to accomplish.

I'm looking forward to sorting this out when I get a few spare hours!

The failure mode could be dangerous in the wrong circumstances, absolutely no warning before it happened.

[paintman]

Well known issue on the 300TDi.
There's a how to here:
http://www.4x4community.co.za/forum/showthread.php...

Edited by paintman on Sunday 24th December 17:34

[100SRV]

Thanks for the link, paint man, the immobiliser has done well to last for 280,000 miles.

I fitted an overdrive to it about a week ago and secured the harness which runs to the seat box part of the immobiliser (it was loose). I'll be interested to see whether a connection has been stressed as a result of the constant wiggling and I caused it to fail.

I presume that bypassing the immobiliser will leave the alarm function intact?

[100SRV]

I had a good look at the immobiliser installation and found the root cause of the problem. I unmated the engine/bulkhead harness connector (Black Sumitomo) and found that the pin terminal for the engine run solenoid signal had broken off inside the receptacle half of the connector. No evidence of corrosion at all. Very strange.

Fault rectified and car fully functional.

[100SRV]

Fault reappeared, firstly causing 60 Amp maxi fuse to blow on a B Road late at night.

I removed whole dash to locate short-circuit. No fault found. Used the car for two weeks and it behaved itself. Intermittent faults are a PITA to resolve.

Reinstall the dash etc after beginning to trust it again and set off North on the M6. Eighty-two miles into the journey the fault reappeared in the outside lane. Fortunately it was a fifty mph limit and I was able to cross into a gap in the roadworks steel barrier. A very lucky escape.

Fault no longer intermittent, it had moved in and brought relatives.

I've isolated it to the engine / immobiliser harness.

Two major concerns;
Failure of Maxi fuse 2 leaves indicators and hazard lights inoperative. At least one of those should be independent of other critical circuits so the vehicle is visible in such an emergency.

The engine stop solenoid is on an unfused feed.

Next job is to strip out the suspect harness, find and eliminate the fault.

Suspect that the defective terminal I found may have had high resistance and the available current allowed the fault to persist and damage the insulation rather than blowing the fuse. If the solenoid had suitable overcurrent protection this could not have happened.

Edited by 100SRV on Monday 12th February 09:02

[100SRV]

Two faults found; ignition supply wire in engine harness. Acute bend and insulation failure probably due to a combination of contamination and stress.



Close-up of wire


Also engine stop solenoid wire pulled in half when removing it from harness, looks like heat failure.