got a new toy but broke it

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peterz3

Member
Posts
11
Location
shropshire
after sorting out why I could not start my disco (no earth on the starter relay) wouldn't start again 2 weeks later, had to bump start(first time swmbo has ever had a bump start) any way found out no power on the r/w wire on the ignition switch so I've fitted a push start button onto the dash found a switch 12v on the fuse box , bingo she now starts
peterz3
 
peterz3 said:
after sorting out why I could not start my disco (no earth on the starter relay) wouldn't start again 2 weeks later, had to bump start(first time swmbo has ever had a bump start) any way found out no power on the r/w wire on the ignition switch so I've fitted a push start button onto the dash found a switch 12v on the fuse box , bingo she now starts
peterz3
Click to expand...

Would it not be better to find out why you had a pyro potential in the car ?
 
ok W/R Disco 300tdi R reg , the immobiliser was playing up not earthing the start relay so I put a eath from the relay straight to a good eather point first time, that worked ok but as I said 2 weeks later the starter relay didn't work on checking there was no 12v on the W/R from the ignition switch that when I found a 12v (fused)on the fuse box (driver side) through a push start switch to the W/R on the relay, a good bodge every thing works now it also means if some one tries to steal it that will have to find the push switch first
peterz3
 
Did the same with my Disco TD5 :p

Except I had to make an security code simulator to fool the engine ECU into thinking that the BCU was still there. :D
 
peterz3 said:
ok W/R Disco 300tdi R reg , the immobiliser was playing up not earthing the start relay so I put a eath from the relay straight to a good eather point first time, that worked ok but as I said 2 weeks later the starter relay didn't work on checking there was no 12v on the W/R from the ignition switch that when I found a 12v (fused)on the fuse box (driver side) through a push start switch to the W/R on the relay, a good bodge every thing works now it also means if some one tries to steal it that will have to find the push switch first
peterz3
Click to expand...
As for the push switch, you could have wired it to the key barrel so at least they'd need the key (even if not immobilised)

You can buy a "Immo Spider" that is supposed to bypass this
 
Sounds very strange to me but if you say so cos AFAIK simply tricking the ECU with the security code it's not enough for a Td5 but i'm not gonna argue on this
 
Well as you have found out, the security ECU removes the earth connection from the starter relay and inhibiting the starting of the engine. Doing what you have done by installing an additional earth supply to the relay therefore bypassing that part of the immobiliser function is the best option.

Not having a12v supply directly from the ignition switch on the white/red wire can only indicate that u have a faulty switch as u have the main 12volts at the switch from the engine bay fuse box.
 
sierrafery said:
Sounds very strange to me but if you say so cos AFAIK simply tricking the ECU with the security code it's not enough for a Td5 but i'm not gonna argue on this
Click to expand...

You have to send the security code and you also need to short the starter relay coil to ground.

It depends how you have interpretted the code, it runs over a certain window
 
Last edited:
sierrafery said:
So all this complicated bodge while you can disable the immobiliser with tester?
Click to expand...

Sorry for not being as clever as you sierrafery. But yes, you can disable the BCU immobiliser with the tester, but you CANNOT turn off the engine ECU immobiliser without removing the EEPROM. OR, you can do what I have done. Which means if I screw the BCU up when wading water, I don't have to worry about the engine not running.

And I wouldn't call it overly complicated and I wouldn't call it a bodge, if anything, it's a sensible bypass that doesn't make it completely unsecure, as I can remove the signal injection from the vehicle and the engine will NOT run.
 
Once the immobiliser disabled with tester the engine ECU goes to "no code" status so it will start abd run anyway without BCU involvment albeit if you do such extreme wading to ruin the BCU the interior fusebox or ECU can be hurt at the same time then you have greater problems anyway, or what if that signal emulator fails?... i'm not against wiring or other mods but i dont like such ''radical" intrusions that's all... i know even simpler ways to bypass things but i'm not gonna make them public nor do them on my car... i woukld'n call ''sensible" a bypass which involves an additional PWM signal generator though IMO anybody is free to "bastardise" his own vehicle
 
Last edited:
sierrafery said:
albeit if you do such extreme wading to ruin the BCU the interior fusebox or ECU can be hurt at the same time then you have greater problems anyway
Click to expand...

Relays and fuses are easier to fault find and repair than a ruined BCU. And from my experience, a lot more resilient than ECUs.

And before you mention that the engine ECU is mounted under the bonnet, it's not there anymore, it's up high in the cabin. ;)
 
sierrafery said:
Yopu should know that the interior fusebox is called IDM, it's far more complex than a simple relay and fuse holder;)
Click to expand...
I think that you seem to be under the impression this is a permanent fix, which is never my intention. Its a get me out of the s**t bypass ;)
 
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