P38A Strange no-start issue, immobiliser related?

This site contains affiliate links for which LandyZone may be compensated if you make a purchase.
Datatek said:
12 volts is as good as flat from the point of view of the electronics, no surprise it fails to start sometimes.
The battery voltage should be no lower than 12.6 volts, either there is a drain flattening the battery or the battery is toast. Check for wet carpet and underlay in the drivers footwell.
Click to expand...

I've tested with a more accurate meter and I'm reading 12.46 V.. Based on DanClarke's reply about voltages, this would probably be OK/Passable.

Will check for wet carpet + underlay in the drivers footwell, thank you.

I've been in contact with Simon at ECUX who produces immobiliser bypass boards, and he mentioned that I can check if my immobiliser has already been partially bypassed by putting the car in Drive or Reverse and trying to start it... apparently if the BECM is doing it's job and hasn't been bypassed, then the car shouldn't crank... mine does.

However, as I've already learnt that some model years do crank when immobilised, and some don't, I'm not sure anymore!
 
domlinson said:
I've tested with a more accurate meter and I'm reading 12.46 V.. Based on DanClarke's reply about voltages, this would probably be OK/Passable.

Will check for wet carpet + underlay in the drivers footwell, thank you.

I've been in contact with Simon at ECUX who produces immobiliser bypass boards, and he mentioned that I can check if my immobiliser has already been partially bypassed by putting the car in Drive or Reverse and trying to start it... apparently if the BECM is doing it's job and hasn't been bypassed, then the car shouldn't crank... mine does.

However, as I've already learnt that some model years do crank when immobilised, and some don't, I'm not sure anymore!
Click to expand...
I think this is erroneous. Unless the vehicle is in "N" or "P" the XYZ switch input/feedback to the BeCM logic always prevents cranking. It is a failsafe to prevent runaway cars killing people. So if it cranks then your car thinks it is in N or P, it is just missing the permission to fire.
It really does sound like an erroneous "disable" to me.
 
Last edited:
Datatek said:
12 volts is as good as flat from the point of view of the electronics, no surprise it fails to start sometimes.
The battery voltage should be no lower than 12.6 volts, either there is a drain flattening the battery or the battery is toast. Check for wet carpet and underlay in the drivers footwell.
Click to expand...
On the most recent battery I've bought, there's a sticker that says 12.1v is 50% discharged, which is also as low as a battery should go (for a brief period)
 
domlinson said:
I've tested with a more accurate meter and I'm reading 12.46 V.. Based on DanClarke's reply about voltages, this would probably be OK/Passable.

Will check for wet carpet + underlay in the drivers footwell, thank you.

I've been in contact with Simon at ECUX who produces immobiliser bypass boards, and he mentioned that I can check if my immobiliser has already been partially bypassed by putting the car in Drive or Reverse and trying to start it... apparently if the BECM is doing it's job and hasn't been bypassed, then the car shouldn't crank... mine does.

However, as I've already learnt that some model years do crank when immobilised, and some don't, I'm not sure anymore!
Click to expand...
According to my battery info, a lead calcium battery is 80% discharged at 12.4 volts. As such the voltage woud drop to unacceptable levels when cranking.
As others have said, no version of the P38 auto will crank unless the lever is in P or N, it has nothing at all to do with the immobilser.
 
Datatek said:
According to my battery info, a lead calcium battery is 80% discharged at 12.4 volts. As such the voltage woud drop to unacceptable levels when cranking.
As others have said, no version of the P38 auto will crank unless the lever is in P or N, it has nothing at all to do with the immobilser.
Click to expand...
Mine (2000/thor 4.0) will not crank when immobilised, just beeps with a message on the dash to press fob, or words to that effect. I disabled the immobiliser requirement with the nano
 
The plot thickens... It sounds like something could have been done to mine, as it will crank when it is in Drive/Reverse, and it cranks when immobilised... although now I'm not sure if it is actually immobilised or not, as there are no messages on the dash.

DanClarke has kindly offered to plug his Nanocom into my P38 in the next few days, so fingers crossed that helps somehow.
 
domlinson said:
The plot thickens... It sounds like something could have been done to mine, as it will crank when it is in Drive/Reverse, and it cranks when immobilised... although now I'm not sure if it is actually immobilised or not, as there are no messages on the dash.

DanClarke has kindly offered to plug his Nanocom into my P38 in the next few days, so fingers crossed that helps somehow.
Click to expand...
Does it show D or R etc on the dash while cranking? Regardless what light is on the gear change
 
domlinson said:
However, as I've already learnt that some model years do crank when immobilised, and some don't, I'm not sure anymore!
Click to expand...

Yes but they should not crank unless in P or N.
1 of the downsides (i have read) when removing the requirement for the security code to the engine ECU to enable start, is the fact they will crank in other gear positions.

As you can cycle it and it starts have you checked relays and fuses for ignition and fuel? can you hear the fuel pump buzz when it wont start? have you checked for spark when you have no start.
Is the green ring around the ignition lighting up cos that has something to do with the key sync when you put in the ignition key and sending of codes.

Cos you can bet when you visit @DanClarke it wont play up and will all look fine.

kermit_rr said:
Mine (2000/thor 4.0) will not crank when immobilised, just beeps with a message on the dash to press fob, or words to that effect. I disabled the immobiliser requirement with the nano
Click to expand...

This only disables something in the BECM it doesnt stop the engine ECU needing the "ok to run" code from the BECM.

J
 
kermit_rr said:
Does it show D or R etc on the dash while cranking? Regardless what light is on the gear change
Click to expand...

Yes it does show D or R on the dash whilst it cranks, which is very weird.

I've had the covers off from under the steering column, and I can see that a wire has been spliced in from the back of the ignition switch directly to the fuse box... So I'm guessing someone has rigged the ignition switch to directly enable the starter motor relay, and this is also why the car cranks in gear

marjon said:
Yes but they should not crank unless in P or N.
1 of the downsides (i have read) when removing the requirement for the security code to the engine ECU to enable start, is the fact they will crank in other gear positions.

As you can cycle it and it starts have you checked relays and fuses for ignition and fuel? can you hear the fuel pump buzz when it wont start? have you checked for spark when you have no start.
Is the green ring around the ignition lighting up cos that has something to do with the key sync when you put in the ignition key and sending of codes.

Cos you can bet when you visit @DanClarke it wont play up and will all look fine.

This only disables something in the BECM it doesnt stop the engine ECU needing the "ok to run" code from the BECM.

J
Click to expand...

Thanks marjon, I'll give those things a try and report back!

At this point, I am tempted to remove the bodge wire that connects the ignition barrel to the fuse box (presumably starter relay) and see how it behaves... For all I know it might never crank with that wire disconnected...
 
domlinson said:
Yes it does show D or R on the dash whilst it cranks, which is very weird.

I've had the covers off from under the steering column, and I can see that a wire has been spliced in from the back of the ignition switch directly to the fuse box... So I'm guessing someone has rigged the ignition switch to directly enable the starter motor relay, and this is also why the car cranks in gear

Thanks marjon, I'll give those things a try and report back!

At this point, I am tempted to remove the bodge wire that connects the ignition barrel to the fuse box (presumably starter relay) and see how it behaves... For all I know it might never crank with that wire disconnected...
Click to expand...
That might be the case, but at least you can put it back on temporarily to return to the status-quo.
R1712 is the Fuel relay according to the ETG, and it gets switched on by the BeCM. I guess Air we can largely take for granted for starting, but fuel & spark can be checked. :)
 
Last edited:
marjon said:
Yes but they should not crank unless in P or N.
1 of the downsides (i have read) when removing the requirement for the security code to the engine ECU to enable start, is the fact they will crank in other gear positions.

As you can cycle it and it starts have you checked relays and fuses for ignition and fuel? can you hear the fuel pump buzz when it wont start? have you checked for spark when you have no start.
Is the green ring around the ignition lighting up cos that has something to do with the key sync when you put in the ignition key and sending of codes.

Cos you can bet when you visit @DanClarke it wont play up and will all look fine.



This only disables something in the BECM it doesnt stop the engine ECU needing the "ok to run" code from the BECM.

J
Click to expand...
Absolutely not true, disabling the immobilser does not allow cranking in other gears.
 
Datatek said:
Absolutely not true, disabling the immobilser does not allow cranking in other gears.
Click to expand...
+1.
I think that the BeCM is in charge of whether power gets to the starter solenoid, and it will only allow cranking if it thinks the gearbox is in P or N. ;-)
upload_2022-10-6_16-29-17.png
 
Datatek said:
Absolutely not true, disabling the immobilser does not allow cranking in other gears.
Click to expand...

The engine Ecu is not the BECM side of immobiliser it’s different as you know.
Why not have a read. These are just the first I have found, can’t find the 1 that says about the need for caution as it can start in gear.
But as they say wiring mods to the starter circuit then I think that’s enough.

https://www.ecudecode.co.uk/err5760-gems-8-2-80569a-p38-range-rover-immobiliser-bypass-service/

https://www.ecux.co.uk/index.php?route=product/product&language=en-gb&product_id=56&tag=

J
 
marjon said:
The engine Ecu is not the BECM side of immobiliser it’s different as you know.
Why not have a read. These are just the first I have found, can’t find the 1 that says about the need for caution as it can start in gear.
But as they say wiring mods to the starter circuit then I think that’s enough.

https://www.ecudecode.co.uk/err5760-gems-8-2-80569a-p38-range-rover-immobiliser-bypass-service/

https://www.ecux.co.uk/index.php?route=product/product&language=en-gb&product_id=56&tag=

J
Click to expand...
Immobiliser is a bit of a misnomer, at least it is on the diesel. The EDC immobilises itself when the ignition is switched off, it then requires a mobilisation code from the BECM when starting in order to operate.
I don't see anything in your links that implies the gear interlock is disabled. Immobilisation takes place, as I said, within the EDC, nothing to do with the BECM. I know nothing about the V8 ECU's but they appear to be the same.
The BECM is only needed to re-mobilise the EDC so bypassing the immobiliser is done within the EDC and has no effect on BECM operations.
 
Datatek said:
Immobiliser is a bit of a misnomer, at least it is on the diesel. The EDC immobilises itself when the ignition is switched off, it then requires a mobilisation code from the BECM when starting in order to operate.
I don't see anything in your links that implies the gear interlock is disabled. Immobilisation takes place, as I said, within the EDC, nothing to do with the BECM. I know nothing about the V8 ECU's but they appear to be the same.
The BECM is only needed to re-mobilise the EDC so bypassing the immobiliser is done within the EDC and has no effect on BECM operations.
Click to expand...

If I remember the petrol also give a feedback to the BECM to give the start permission after it has confirmed the code (not sure if it changed at motornic as this is similar to the diesel EDC?)

Anyway here ya go:p 1 do I need to look for more;). As you don’t seem to have looked properly.

https://www.labtronx.com.au/labtronx-products/mobi4

J
 
Last edited:
Thanks for the input everyone. It's an odd one indeed... Hopefully a Nanocom is able to tell me what the issue is and it will lead me to a resolution, whether that's a proper immobiliser bypass like the ones Simon creates at ECUX, or if I send my ECU away to have the immobiliser properly disabled... Or it might tell me that I, in fact, don't have an immobiliser issue at all and it's something else entirely! :D
 
marjon said:
If I remember the petrol also give a feedback to the BECM to give the start permission after it has confirmed the code (not sure if it changed at motornic as this is similar to the diesel EDC?)

Anyway here ya go:p 1 do I need to look for more;). As you don’t seem to have looked properly.

https://www.labtronx.com.au/labtronx-products/mobi4

J
Click to expand...
The Mobi is just a simple code generator to produce the code required for mobilisation, it is not an immobiliser bypass.
 
Datatek said:
The Mobi is just a simple code generator to produce the code required for mobilisation, it is not an immobiliser bypass.
Click to expand...

It means the engine ecu does not need any permission from the BECM to run. Now I would consider that an immobiliser bypass.
If all the BECM security was going off including the Alarm siren you could still start it:eek:.

We really don’t know in this case what is what but things point towards it.

J
 
domlinson said:
Thanks for the input everyone. It's an odd one indeed... Hopefully a Nanocom is able to tell me what the issue is and it will lead me to a resolution, whether that's a proper immobiliser bypass like the ones Simon creates at ECUX, or if I send my ECU away to have the immobiliser properly disabled... Or it might tell me that I, in fact, don't have an immobiliser issue at all and it's something else entirely! :D
Click to expand...

Have you checked the relays and fuses?

My Gems (no alarm state) would turn over but not start. Squirt of easy start proved I had spark:).
No pressure at fuel rail, with fuel pump relay bridged proved still no pressure so it has a dead in tank fuel pump.
These things need to be eliminated.
J
 
You must log in or register to reply here.

Similar threads

G
TD5 defender immobilizer issue
Replies
2
Views
300
gary brion
G
P
Freelander 1 L-Series Bosch diesel ECU replacement process?
Replies
8
Views
552
pscan.eu
P
TimoTS
Range Rover classic 3.9EFI no oil visible under oil fill cap.
Replies
19
Views
644
aj1954
aj1954
F
P38A Starting issues.
Replies
7
Views
783
kermit_rr
kermit_rr
D
Discovery 1 300tdi immobiliser
Replies
1
Views
421
Stanleysteamer
Stanleysteamer
Back
Top