Land Rover Repair: Keyless entry on 98 Disco?, rf receivers, t4 system

Question
QUESTION: John,

Ok, first before I begin, let me refer to two Land rover Dicoverys, I series. The '99 will be "A", '98 will be "B".

Have had A for 3.5 years, just purchased B as a project with low miles and slight front end damage. Have now fixed up B to drive and while B did not have a keyless remote, A did - A is being sold off.

I decided tonight to simply swap the receiver boxes and B will now lock and unlock, start and drive with no problems.

A will not start. If I turn the key, it turns on, but no starter. If I turn on the headlights, the starter will spin, but not start.

If B is fine, then what has happened to A? Is it possible I simply disturbed something else under the dash in A to cause this?

Thanks,
Michael

ANSWER: The remotes send signals to the engine control units to authorize or inhibit starting. Whenever you disconnect or tamper with them one of the steps in the service procedure is to realign the units with the LR test system.  You are simply lucky that either truck ran after unhooking the alarm controllers!

If you want the other truck to run you will need to connect an Autologic or T4 system and go through the security align procedure.  If you disconnect and swap boxes again there is a high likelihood neither truck will run when you are done.

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

QUESTION: John,

Thanks for answering so quickly. I only elected to change the RF receivers when my manual indicated there would be no other issue, and the '98 is performing perfectly as far as this is concerned. I called our local Land Rover/Jaguar/Porsche dealership today and spoke with the LR service mgr. who feels that the '99 is not immobilized, since the starter is working at all, and that there is another electrical error occurring here since the starter will spin with the headlights on. (If I didn't mention before, I'm not sure why I tried that, but it does) Would you have any thoughts on this? I'll take another look tonight, but is there any other definitive measure of whether or not it is immobilized?

Thanks again,
Michael

Answer
If the only change is the swapping of the alarm/lock controllers then I don't see where else to look but there.  It's certainly possible that you have some coincidental failure, but if so, it could be anything at all.  I just know I see people spend hours trying to trace wires when a few minutes with the proper test equipment will tell the story on the live data screens.

In the absence of a tester, all you can do is take the electrical troubleshooting manual and go through the start and run circuits.