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?
Are you sure that the fuel pump circuit is actually immobilised? Mine certainly is not. Some cars are but many just have the starter solonoid and the ignition circuit immobilised.
The overloaded immobiliser relay problem you mention was I understand regarding the starter solonoid not the fuel pump circuit.
I replaced my Meta 99 T2 alarm module alone retaining the original immobiliser, the two do require synchronising to work together and although mine synchronised easily I understand that it may not be possible if this procedure has been carried out a few times in the past. A new alarm module also required a new Siren unit as the old siren was incompatible
If you are sure that your fuel pump is immobilised why not just bypass it, there are already far to many plugs/sockets in the pump circuit to cause intermittent problems without adding more!
The overloaded immobiliser relay problem you mention was I understand regarding the starter solonoid not the fuel pump circuit.
I replaced my Meta 99 T2 alarm module alone retaining the original immobiliser, the two do require synchronising to work together and although mine synchronised easily I understand that it may not be possible if this procedure has been carried out a few times in the past. A new alarm module also required a new Siren unit as the old siren was incompatible
If you are sure that your fuel pump is immobilised why not just bypass it, there are already far to many plugs/sockets in the pump circuit to cause intermittent problems without adding more!
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
I had an identical problem in that the fuel pump would only start intermittently. And originally thought that the immobiliser could be the problem. After tracing the complete fuel pump circuit:
http://www.bertram-hill.com/griffith-wiring.html
I realised that only the starter solenoid and the ignition were isolated on my car (96 Griffith 500).
Even after tracing and checking the complete fuel pump circuit I never did find the fault. As each plug/socket was cleaned during the process I concluded that it must have been a dirty contact in one of the plugs/sockets. No further problems experienced in over two years.
http://www.bertram-hill.com/griffith-wiring.html
I realised that only the starter solenoid and the ignition were isolated on my car (96 Griffith 500).
Even after tracing and checking the complete fuel pump circuit I never did find the fault. As each plug/socket was cleaned during the process I concluded that it must have been a dirty contact in one of the plugs/sockets. No further problems experienced in over two years.
Before diagnosing a fault it's essential to properly understand how a system really works, in this case the immobiliser controls two circuits.
1. The starter solenoid
2. The ECU
The immobiliser does not directly control the fuel pump, it's just people assume it does because when they disengage the immobiliser they hear the fuel pump run for a few seconds to prime the fuel rail, the short initial rail priming run of the fuel pump you're hearing is actually all done by the ECU!
1. Disengage the immobiliser and the ECU becomes live
2. The ECU then runs the pump for a few seconds to prime the fuel rail
3. The ECU will not run the pump any longer than a few seconds until it sees a signal from the coil confirming the engine is either cranking or running
So if you're not hearing the pump buzz for a few seconds you must first establish if the ECU is getting it's 12v, the ECU has a dedicated relay so checking for 12v here is the best place to start but may lead you to confirming the immobiliser (which is really just a switch) is not supplying 12v to the ECU.
The ECU relay is one of the pair that dangle precariously in the passenger footwell, confusingly the other one (with the blue plug) is a dedicated fuel pump relay, ignore this fuel pump relay initially and start by checking your ECU is genuinely seeing 12v on immobiliser disengagement, because if it isn't your fuel pump will never run!
At this point it may be helpful to rig up a little warning light so from the drivers seat you can see the ECU is genuinely getting 12v when it should, take the live and earth from your ECU relay and position your warning light where you can see it easily when you're sat behind the wheel....
http://www.carbuildersolutions.com/uk/small-chrome...
At the same time wire a blue warning light to the fuel pump relay...
http://www.carbuildersolutions.com/uk/small-chrome...
I'd go as far to suggest these two little warning lights could make a useful permanent addition for all, even if you're not having issues these two circuits are well known to be temperamental so having the warning lights would offer useful & reassuring information.
If everything is working as it should this is what you should see:
1. When you turn the key on and disengage your immobiliser your little ECU light should illuminate
2. At the same time your fuel pump light will illuminate but only for the few seconds the ECU deems necessary to prime the fuel rail to prepare for the start, your fuel pump light will then extinguish
3. As long as the ignition switch is left on the ECU light should remain illuminated, but the fuel pump light will only come back on when the ECU sees a signal from the coil confirming the engine is either cranking or running
4. Crank and start the engine, as soon as you crank the engine you should see your blue fuel pump light come back on, it will then remain illuminated all the time as will the ECU light until you turn the engine off
Your little twin warning light panel will tell you everything you need to know from the comfort of the driver's seat, you'll have visual confirmation you've successfully disengaged your immobiliser, that both ECU & fuel pump are seeing 12v when starting the engine and all the time you're driving the car.
This real time information could prove invaluable if you suspect you're experience an intermittent fault on theses circuits, for example:
1. If you're seeing neither the ECU or fuel pump lights after disengaging your immobiliser you'll know to suspect the immobiliser
2. If you're seeing the ECU light but not the fuel pump light you know to check your fuel pump relay
3. If the fuel pump light comes on for a few seconds when disengaging the immobiliser but fails to illuminate when you crank the engine you know the ECU is not seeing the "engine cranking/running" signal from the coil
Keep in mind... wired as described your fuel pump warning light is really just telling you your fuel pump relay is seeing 12v and working correctly, it does not actually tell you if the fuel pump itself is getting the 12v from the relay or the pump earth is intact. The wiring from the fuel pump relay to the fuel pump and the connections to the very exposed fuel pump itself are both additional and common sources of failure so if your little fuel pump warning illuminates as it should but the pump doesn't buzz I'd be checking those corrosion prone contacts on the pump.
Two little lights, lots of useful information... well worth a tenner and 30 minutes to wire them up...
Hope this helps?
1. The starter solenoid
2. The ECU
The immobiliser does not directly control the fuel pump, it's just people assume it does because when they disengage the immobiliser they hear the fuel pump run for a few seconds to prime the fuel rail, the short initial rail priming run of the fuel pump you're hearing is actually all done by the ECU!
1. Disengage the immobiliser and the ECU becomes live
2. The ECU then runs the pump for a few seconds to prime the fuel rail
3. The ECU will not run the pump any longer than a few seconds until it sees a signal from the coil confirming the engine is either cranking or running
So if you're not hearing the pump buzz for a few seconds you must first establish if the ECU is getting it's 12v, the ECU has a dedicated relay so checking for 12v here is the best place to start but may lead you to confirming the immobiliser (which is really just a switch) is not supplying 12v to the ECU.
The ECU relay is one of the pair that dangle precariously in the passenger footwell, confusingly the other one (with the blue plug) is a dedicated fuel pump relay, ignore this fuel pump relay initially and start by checking your ECU is genuinely seeing 12v on immobiliser disengagement, because if it isn't your fuel pump will never run!
At this point it may be helpful to rig up a little warning light so from the drivers seat you can see the ECU is genuinely getting 12v when it should, take the live and earth from your ECU relay and position your warning light where you can see it easily when you're sat behind the wheel....
http://www.carbuildersolutions.com/uk/small-chrome...
At the same time wire a blue warning light to the fuel pump relay...
http://www.carbuildersolutions.com/uk/small-chrome...
I'd go as far to suggest these two little warning lights could make a useful permanent addition for all, even if you're not having issues these two circuits are well known to be temperamental so having the warning lights would offer useful & reassuring information.
If everything is working as it should this is what you should see:
1. When you turn the key on and disengage your immobiliser your little ECU light should illuminate
2. At the same time your fuel pump light will illuminate but only for the few seconds the ECU deems necessary to prime the fuel rail to prepare for the start, your fuel pump light will then extinguish
3. As long as the ignition switch is left on the ECU light should remain illuminated, but the fuel pump light will only come back on when the ECU sees a signal from the coil confirming the engine is either cranking or running
4. Crank and start the engine, as soon as you crank the engine you should see your blue fuel pump light come back on, it will then remain illuminated all the time as will the ECU light until you turn the engine off
Your little twin warning light panel will tell you everything you need to know from the comfort of the driver's seat, you'll have visual confirmation you've successfully disengaged your immobiliser, that both ECU & fuel pump are seeing 12v when starting the engine and all the time you're driving the car.
This real time information could prove invaluable if you suspect you're experience an intermittent fault on theses circuits, for example:
1. If you're seeing neither the ECU or fuel pump lights after disengaging your immobiliser you'll know to suspect the immobiliser
2. If you're seeing the ECU light but not the fuel pump light you know to check your fuel pump relay
3. If the fuel pump light comes on for a few seconds when disengaging the immobiliser but fails to illuminate when you crank the engine you know the ECU is not seeing the "engine cranking/running" signal from the coil
Keep in mind... wired as described your fuel pump warning light is really just telling you your fuel pump relay is seeing 12v and working correctly, it does not actually tell you if the fuel pump itself is getting the 12v from the relay or the pump earth is intact. The wiring from the fuel pump relay to the fuel pump and the connections to the very exposed fuel pump itself are both additional and common sources of failure so if your little fuel pump warning illuminates as it should but the pump doesn't buzz I'd be checking those corrosion prone contacts on the pump.
Two little lights, lots of useful information... well worth a tenner and 30 minutes to wire them up...
Hope this helps?
Its a fair point, as is to point out the immobiliser only gives you a certain amount of time to start the car before it resets itself.
I'm sure most people know this already but it can add to the confusion when you're suffering from and trying to diagnose a fault especially if that fault is an intermittent one.
In my opinion the reset time is way too short making the system both frustrating and not very user friendly, because of this frustrating feature the TVR alarm specialists commonly extend the reset time when replacing the system.
Due to the system's well known unreliability and frustratingly short reset time theres a strong argument to completely bypass the immobiliser controlled circuits altogether. The immobiliser is just a switch at the end of the day, it's meant to be a smart and convenient switch but is actually a source of unreliability, failed starts and frustrating fob pressing and cycling of the ignition key.
As such a complete bypass with the inclusion of a hidden latching switch is a very appealing solution that offers unparalleled simplicity and complete reliability, it's cheap too.
I'm sure most people know this already but it can add to the confusion when you're suffering from and trying to diagnose a fault especially if that fault is an intermittent one.
In my opinion the reset time is way too short making the system both frustrating and not very user friendly, because of this frustrating feature the TVR alarm specialists commonly extend the reset time when replacing the system.
Due to the system's well known unreliability and frustratingly short reset time theres a strong argument to completely bypass the immobiliser controlled circuits altogether. The immobiliser is just a switch at the end of the day, it's meant to be a smart and convenient switch but is actually a source of unreliability, failed starts and frustrating fob pressing and cycling of the ignition key.
As such a complete bypass with the inclusion of a hidden latching switch is a very appealing solution that offers unparalleled simplicity and complete reliability, it's cheap too.
Edited by ChimpOnGas on Wednesday 31st August 13:39
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.
I commend you for your determination Ian, but sometimes the simplest solutions are the best 
To the most part the Chimaera is a simple uncomplicated car and in my opinion is all the better for that.
Follow this commendable theme by removing the few complications that unnecessarily add frustration and unreliability.
Dave.
To the most part the Chimaera is a simple uncomplicated car and in my opinion is all the better for that.
Follow this commendable theme by removing the few complications that unnecessarily add frustration and unreliability.
Dave.
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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