Immobiliser replacement time?
Discussion
I have read many of the immobiliser thread issues on here and am aware of the use of the wrong relays in the immobiliser by TVR. My problem however is that it seems to be the ECU 12V output that is intermittent.
Strangely, it happens more when the car is cold than when warm! I will unlock the car / disable the immobilser and when I turn on the ignition, there is no relay click / fuel pump running.
If I turn the ignition off and back on (without pressing the fob or using the touchkey), sometimes more than once, I then get the familiar whine of fuel pump pressurising the fuel rail. I have tried changing the 2 usual suspect relays and the fault is still there.
I have traced the responsible wires and am aware of how to bypass if necessary but I really still want to have an immobiliser. I don't believe the ccts have been swapped over.
Abacus alarms do a direct replacement for the M36T2 fitted to my 2000 reg Chimaera and seem to be well aware of the problems: http://www.abacuscaralarms.co.uk/tvr-alarms.html
I realise this will mean the button on my fob will then only open / close the car and set the alarm. I will have to put the little plastic touchkey in the socket to disable the immobilser separately.
I know many owners have had the whole alarm / immobiliser system replaced but I'm considering that just replacing the faulty M36T2 unit should work, especially since Abacus supply it with the relays correctly used and with a socket to plug it into the existing loom. Has anyone else done this?
Strangely, it happens more when the car is cold than when warm! I will unlock the car / disable the immobilser and when I turn on the ignition, there is no relay click / fuel pump running.
If I turn the ignition off and back on (without pressing the fob or using the touchkey), sometimes more than once, I then get the familiar whine of fuel pump pressurising the fuel rail. I have tried changing the 2 usual suspect relays and the fault is still there.
I have traced the responsible wires and am aware of how to bypass if necessary but I really still want to have an immobiliser. I don't believe the ccts have been swapped over.
Abacus alarms do a direct replacement for the M36T2 fitted to my 2000 reg Chimaera and seem to be well aware of the problems: http://www.abacuscaralarms.co.uk/tvr-alarms.html
I realise this will mean the button on my fob will then only open / close the car and set the alarm. I will have to put the little plastic touchkey in the socket to disable the immobilser separately.
I know many owners have had the whole alarm / immobiliser system replaced but I'm considering that just replacing the faulty M36T2 unit should work, especially since Abacus supply it with the relays correctly used and with a socket to plug it into the existing loom. Has anyone else done this?
Fuel pump cct is definitely immobilised. Should be on all Chimaera I thought?? Without fuel pressure, the car won't start and when it is working properly, I get a whine for about 3/4 sec to establish it.
Some threads on here have mentioned that the cct interrupted by the immobiliser is actually the power to the ECU, which in turn initiates the relays that allow power to the fuel pump. Either way, the later models have 2 ccts interrupted.
Bypassing the starter solenoid cct is possible (no details here) because 12V potential is only present on one of the cables when the key is in pos 3 (crank). This is what is required for the starter cct.
My car does not always start first turn of the key
so 12V would be required for the ECu / fuel ccts at both position 2 and 3 to maintain fuel pressure. Isolating a 12V supply from the battery via an additional bypass switch was something I considered but it just makes it more complicated. There are insurance implications too if it is completely bypassed.
I'm glad you managed to just replace the alarm module without issue so I may try replacing the M36T2. However, sod's law states it will be fine for weeks now! The fact it pairs with the M99T2 unit may be possible but it depends on how many memory spaces have been used according to Abacus.
Some threads on here have mentioned that the cct interrupted by the immobiliser is actually the power to the ECU, which in turn initiates the relays that allow power to the fuel pump. Either way, the later models have 2 ccts interrupted.
Bypassing the starter solenoid cct is possible (no details here) because 12V potential is only present on one of the cables when the key is in pos 3 (crank). This is what is required for the starter cct.
My car does not always start first turn of the key
so 12V would be required for the ECu / fuel ccts at both position 2 and 3 to maintain fuel pressure. Isolating a 12V supply from the battery via an additional bypass switch was something I considered but it just makes it more complicated. There are insurance implications too if it is completely bypassed.I'm glad you managed to just replace the alarm module without issue so I may try replacing the M36T2. However, sod's law states it will be fine for weeks now! The fact it pairs with the M99T2 unit may be possible but it depends on how many memory spaces have been used according to Abacus.
Edited by ianwayne on Tuesday 30th August 17:36
Thanks for the comprehensive description. Connecting up extra warning lamps is to be applauded. It was reading old posts from yourself that led me to trace what wires do what into / out of my immobiliser.
I now have access to it draping through the passenger glove / flap thing so I can do in situ / power on testing with a multimeter. Having 2 sets of working fobs has helped too when diagnosing from the passenger side!
I am poised to check the cable from the immobiliser for 12V when the pump does NOT run as it should. (Typically, it has worked fine every time I've tried it; 10 times on the trot today). If I have 12V, then the ECU / fuel cct is defective somehere, although i have already tried replacement relays. If I don't, as I suspect will be the case, I believe the immobiliser unit is at fault. I have had cranking issues as well previously so the immobiliser may well be on the way out.
Doing more diagnosis, I have noticed that as advertised, it takes just over 15 seconds for the immobiliser to enable after turning the ignition off. However, one of the relays de-energises with an audible click only 6 seconds after power off. Not sure this is significant. Most likely the fuel pump hold-on cct de-energising. If I turn the ignition back on between 6s and 15s after turning it off, the fuel pump runs again OK.
I have removed the immobiliser touchkey socket from the steering wheel shroud and traced it into the loom where it goes 2 ways (to the alarm and to the immobiliser to synchronise them). It has a screw on nut / shroud so the dash top has to come off completely to trace and remove the loom tie wraps. What fun!
By disconnecting it and connecting it directly to the M38T2, I have simulated having a replacement one but with the original M99 alarm. As I suspected, the car unlocks and disarms from the fob OK, but the little touchkey has to be used to disable the immobiliser. It starts OK with the alarm not going off. I could live with this.
Next time I unlock, get in the car, turn on the key and there is no fuel pump whirr, I will be able to do more diagnosis.
I now have access to it draping through the passenger glove / flap thing so I can do in situ / power on testing with a multimeter. Having 2 sets of working fobs has helped too when diagnosing from the passenger side!
I am poised to check the cable from the immobiliser for 12V when the pump does NOT run as it should. (Typically, it has worked fine every time I've tried it; 10 times on the trot today). If I have 12V, then the ECU / fuel cct is defective somehere, although i have already tried replacement relays. If I don't, as I suspect will be the case, I believe the immobiliser unit is at fault. I have had cranking issues as well previously so the immobiliser may well be on the way out.
Doing more diagnosis, I have noticed that as advertised, it takes just over 15 seconds for the immobiliser to enable after turning the ignition off. However, one of the relays de-energises with an audible click only 6 seconds after power off. Not sure this is significant. Most likely the fuel pump hold-on cct de-energising. If I turn the ignition back on between 6s and 15s after turning it off, the fuel pump runs again OK.
I have removed the immobiliser touchkey socket from the steering wheel shroud and traced it into the loom where it goes 2 ways (to the alarm and to the immobiliser to synchronise them). It has a screw on nut / shroud so the dash top has to come off completely to trace and remove the loom tie wraps. What fun!
By disconnecting it and connecting it directly to the M38T2, I have simulated having a replacement one but with the original M99 alarm. As I suspected, the car unlocks and disarms from the fob OK, but the little touchkey has to be used to disable the immobiliser. It starts OK with the alarm not going off. I could live with this.Next time I unlock, get in the car, turn on the key and there is no fuel pump whirr, I will be able to do more diagnosis.
Just changing the whole alarm & immobiliser system is the obvious answer. But the engineer / curiosity in me wants to know exactly what is happening and why. I've the time at the moment to diagnose it as much as I can.
I won't explain how to bypass the immobiliser here (obviously), your email last year pointed the way, but since there are 9 wires (actually 8) plus the touchkey socket ribbon in use, there must be some other ccts involved rather than just 2 x 12V supply paths. The later ones like mine only disable 2 ccts, apparenty, not 3 like the earlier ones. In fact, it's no secret, and on the Abacus website that pin 9 isn't actually used so one wire of the 9 is redundant.
Additionally, despite many people's intentions, there will likely come a time to sell their car on. And explaining that the immobiliser is or may have to be bypassed occasionally via another switch to start the car is not going to be that popular! Others may not mind, but I'd like it to work as intended if possible.
Now that I've being using the touchkey all the time, and I haven't had an issue, I'm having doubts. If the immobiliser re-establishes itself, I'm wondering if turning the ignition on, and then pressing the fob button to disable the immobiliser has been flaky all along!
I've been for a spin this afternoon and it's hot here. I've stopped half a dozen times and let the immobiliser kick in. Every time I have disabled it using the touchkey, the car has started fine. You're right about intermittent faults being the hardest to trace. I bypassed the start cct relays earlier this year because of problems but have now put it all back as standard and it is starting even when very hot! I fully expect it to happen next time I fuel up.
I won't explain how to bypass the immobiliser here (obviously), your email last year pointed the way, but since there are 9 wires (actually 8) plus the touchkey socket ribbon in use, there must be some other ccts involved rather than just 2 x 12V supply paths. The later ones like mine only disable 2 ccts, apparenty, not 3 like the earlier ones. In fact, it's no secret, and on the Abacus website that pin 9 isn't actually used so one wire of the 9 is redundant.
Additionally, despite many people's intentions, there will likely come a time to sell their car on. And explaining that the immobiliser is or may have to be bypassed occasionally via another switch to start the car is not going to be that popular! Others may not mind, but I'd like it to work as intended if possible.
Now that I've being using the touchkey all the time, and I haven't had an issue, I'm having doubts. If the immobiliser re-establishes itself, I'm wondering if turning the ignition on, and then pressing the fob button to disable the immobiliser has been flaky all along!
I've been for a spin this afternoon and it's hot here. I've stopped half a dozen times and let the immobiliser kick in. Every time I have disabled it using the touchkey, the car has started fine. You're right about intermittent faults being the hardest to trace. I bypassed the start cct relays earlier this year because of problems but have now put it all back as standard and it is starting even when very hot! I fully expect it to happen next time I fuel up.
Edited by ianwayne on Wednesday 31st August 16:17
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