Immobiliser mischief?

Departed · 23rd December 2007, 14:35

Immobilser and locking aren't actually linked (other than they both live inside the key head).

The alarm / locking transmits when you press they fob. The immobilser has a transponder chip which only transmits when it's in the ignition lock. The ECUs that receive the signals are different too.

So sorry, the theory doesn't stack up, and as pointed out an immo lockout also prevents cranking.

So cam sensor, fuel pumps, or glow plugs. If it's OK when cold, but always fails with a hot engine, I'd plump for cam sensor too.

Johnny2R · 30th December 2007, 12:50

Quote:

Originally Posted by lowedb

Immobilser and locking aren't actually linked (other than they both live inside the key head).

The alarm / locking transmits when you press they fob. The immobilser has a transponder chip which only transmits when it's in the ignition lock. The ECUs that receive the signals are different too.

So sorry, the theory doesn't stack up, and as pointed out an immo lockout also prevents cranking.

So cam sensor, fuel pumps, or glow plugs. If it's OK when cold, but always fails with a hot engine, I'd plump for cam sensor too.

The odd thing is that 99.9% of the time the car starts without a problem. As I said, this problem has occurred just three times in the 18 months I've owned the car. In each case I've done something unusual with the unlocking immediately prior to attempting to start, hence my suspicion that it was something related. Surely if I had a faulty cam sensor or the like, I'd get regular problems starting, wouldn't I? There is normally no problem whatsoever starting.

As I mentioned, there was no power to the fuel pumps, which would appear to rule them out. How would a problem with glowplugs manifest itself?

Also, how do I check out the fuel pump relay?

Johnny2R · 4th January 2008, 15:47

Hmm, the mysterious complete non-starting has occurred again. I just had an MOT test done (which the car passed, to my relief), and the mechanic could not start the car to drive it away from the test bay. Same again, turns over without so much as a cough. He said he had initially locked the car, then immediately unlocked it again before attempting to drive away (once again a slightly unusual sequence of actions).

I was completely unable to start it, despite numerous locks, unlocks, etc. Then I opened the bonnet, unplugged the RoverRon Synergy unit, plugged it back in again but turned it off, and then it started straight away. So, I turned off the engine and turned the Synergy back on and tried again. Once again it started fine. What might this point to? I doubt it's a fault with the Synergy because on the previous occasions when the problem has occurred, I haven't done what I did this time. It seems to me in some way ECU related, but I can't think how.

Incidentally, the smoke reading in the MOT test was negligible, despite the Synergy being on its highest setting (10), which I'm very pleased with. The engine runs wonderfully and certainly doesn't show its 166,000 miles.

David3807 · 4th January 2008, 16:23

Do you have a spare key and have you tried it ??

Johnny2R · 4th January 2008, 17:39

I do have a spare key. I haven't had it with me when the non-starting problem has occurred. Perhaps I'll take to carrying it with me. Why would the spare key help? You reckon it could be some key fob related issue?

Departed · 4th January 2008, 19:04

Interesting.

I still can't see how the locking and immobilser are related. It's not any sort of functional relationship, so it must be something odd like earthing or power supply if it is related at all.

Honestly, there is really no working involvement with immobilser and locking. And the fact that the car turns over backs up that the immo is OK, it wouldn't even turn over if it was unhappy. I'll photograph the inside of my spare key to show you the two unrelated parts, if you like.

There is a pattern, but try to avoid falling into the trap of fitting the symptoms to what you think it is. Take a step back, and try to see what other clues there might be.

Glow plugs: if these aren't working typically it would be cold starting that's a problem. Failure to start after the MOT probably rules this out.

alan lloyd · 13th February 2008, 13:52

I am having exacly the same problem, doen't start randomly. Today started fine, travelled 50 miles , restarted 3 times, travelled 50 miles, stopped for lunch, refused to start.
I shall be trying again after sending this.
Is it possible to disengage the immobiliser?

EamonnS · 19th May 2008, 16:03

My 75 Tourer has just started playing me up with the immobiliser. What triggers the transponder chip when it is in the ignition lock? Is this a passive transponder or does it rely on a battery in the key? Is there a way of completely bypassing the immobiliser? This is now happening with both of my keys. HELP!!!!!

Quote:

Originally Posted by lowedb

Immobilser and locking aren't actually linked (other than they both live inside the key head).

The alarm / locking transmits when you press they fob. The immobilser has a transponder chip which only transmits when it's in the ignition lock. The ECUs that receive the signals are different too.

So sorry, the theory doesn't stack up, and as pointed out an immo lockout also prevents cranking.

Simon · 19th May 2008, 17:15

In what way is your car playing up? A list of the symptoms will help diagnose the problem as it may not be immoboliser related - for example other electrical gremlins can produce strange results.

Departed · 19th May 2008, 18:57

Hi. The transponder doesn't rely on the battery. The coil around the ignition lock transmits a signal to the chip. The chip powers itself from this signal, and modulates the signal to talk to the immobiliser. The immobiliser also modulates the signal to talk to the chip. It's triggered as you turn the key from off, to accessory.

The battery is for the remote control: in the same box as the transponder, but not connected to it. The transponder has nothing to connect it to anything. You could take the battery out, and the transponder will still work. In fact early cars were meant to have one normal key an one key with only a transponder. Don't know whether this ever happened, but it would explain why so many early cars have only one key.

As I said earlier, the immobiliser would be a little pointless if it could be overcome without a good deal of effort: whoever wanted to steal your car would simply switch off the immobilser and drive your car away.

4th January 2008, 15:47	#3
Johnny2R Gets stuck in Rover 75 CDT Club Tourer Join Date: Apr 2007 Location: Norwich Posts: 712 Thanks: 98 Thanked 47 Times in 24 Posts	Strikes again! Hmm, the mysterious complete non-starting has occurred again. I just had an MOT test done (which the car passed, to my relief), and the mechanic could not start the car to drive it away from the test bay. Same again, turns over without so much as a cough. He said he had initially locked the car, then immediately unlocked it again before attempting to drive away (once again a slightly unusual sequence of actions). I was completely unable to start it, despite numerous locks, unlocks, etc. Then I opened the bonnet, unplugged the RoverRon Synergy unit, plugged it back in again but turned it off, and then it started straight away. So, I turned off the engine and turned the Synergy back on and tried again. Once again it started fine. What might this point to? I doubt it's a fault with the Synergy because on the previous occasions when the problem has occurred, I haven't done what I did this time. It seems to me in some way ECU related, but I can't think how. Incidentally, the smoke reading in the MOT test was negligible, despite the Synergy being on its highest setting (10), which I'm very pleased with. The engine runs wonderfully and certainly doesn't show its 166,000 miles.

13th February 2008, 13:52	#7
alan lloyd Newbie rover 75 touring cdi Join Date: Feb 2008 Location: Farnham Posts: 12 Thanks: 0 Thanked 0 Times in 0 Posts	immobiliser mischief I am having exacly the same problem, doen't start randomly. Today started fine, travelled 50 miles , restarted 3 times, travelled 50 miles, stopped for lunch, refused to start. I shall be trying again after sending this. Is it possible to disengage the immobiliser?

19th May 2008, 18:57	#10
Departed Retired -- Join Date: Jan 2007 Location: -- Posts: 3,785 Thanks: 0 Thanked 4 Times in 4 Posts	Hi. The transponder doesn't rely on the battery. The coil around the ignition lock transmits a signal to the chip. The chip powers itself from this signal, and modulates the signal to talk to the immobiliser. The immobiliser also modulates the signal to talk to the chip. It's triggered as you turn the key from off, to accessory. The battery is for the remote control: in the same box as the transponder, but not connected to it. The transponder has nothing to connect it to anything. You could take the battery out, and the transponder will still work. In fact early cars were meant to have one normal key an one key with only a transponder. Don't know whether this ever happened, but it would explain why so many early cars have only one key. As I said earlier, the immobiliser would be a little pointless if it could be overcome without a good deal of effort: whoever wanted to steal your car would simply switch off the immobilser and drive your car away. Last edited by Departed; 19th May 2008 at 19:00..

23rd December 2007, 14:35	#1
Departed Retired -- Join Date: Jan 2007 Location: -- Posts: 3,785 Thanks: 0 Thanked 4 Times in 4 Posts	Immobilser and locking aren't actually linked (other than they both live inside the key head). The alarm / locking transmits when you press they fob. The immobilser has a transponder chip which only transmits when it's in the ignition lock. The ECUs that receive the signals are different too. So sorry, the theory doesn't stack up, and as pointed out an immo lockout also prevents cranking. So cam sensor, fuel pumps, or glow plugs. If it's OK when cold, but always fails with a hot engine, I'd plump for cam sensor too.

4th January 2008, 16:23	#4
David3807 Posted a thing or two 2002 R75 Conn SE 2.5l Auto Tourer, 2001 R75 Conn SE 2.5 Auto Saloon Join Date: Nov 2006 Location: Gravesend Posts: 1,897 Thanks: 0 Thanked 2 Times in 2 Posts	Do you have a spare key and have you tried it ??

4th January 2008, 17:39	#5
Johnny2R Gets stuck in Rover 75 CDT Club Tourer Join Date: Apr 2007 Location: Norwich Posts: 712 Thanks: 98 Thanked 47 Times in 24 Posts	I do have a spare key. I haven't had it with me when the non-starting problem has occurred. Perhaps I'll take to carrying it with me. Why would the spare key help? You reckon it could be some key fob related issue?

4th January 2008, 19:04	#6
Departed Retired -- Join Date: Jan 2007 Location: -- Posts: 3,785 Thanks: 0 Thanked 4 Times in 4 Posts	Interesting. I still can't see how the locking and immobilser are related. It's not any sort of functional relationship, so it must be something odd like earthing or power supply if it is related at all. Honestly, there is really no working involvement with immobilser and locking. And the fact that the car turns over backs up that the immo is OK, it wouldn't even turn over if it was unhappy. I'll photograph the inside of my spare key to show you the two unrelated parts, if you like. There is a pattern, but try to avoid falling into the trap of fitting the symptoms to what you think it is. Take a step back, and try to see what other clues there might be. Glow plugs: if these aren't working typically it would be cold starting that's a problem. Failure to start after the MOT probably rules this out.

19th May 2008, 17:15	#9
Simon Banned - Join Date: Nov 2006 Location: - Posts: 10,318 Thanks: 0 Thanked 4 Times in 3 Posts	In what way is your car playing up? A list of the symptoms will help diagnose the problem as it may not be immoboliser related - for example other electrical gremlins can produce strange results.