TD5 bcu

Henry.adams · Mar 25, 2023

My 99 d2 has been sitting for over a year I took the bcu off for another truck I want to run it before I take the engine out as a spare but the only bcu I’ve got is off a 03. My understanding is it won’t run with that bcu. However is thought I would give it a go before buying the correct one. To my surprise it cranks but doesn’t start. Is this Likely due to the incorrect bcu? or is it something else it has always been a hard car to start since I took it through deep water so could be related to that. I have Linked the ecu and bcu together and everything like that. I have got a crank position sensor to try tomorrow although I believe the problem is the incorrect bcu anyone know before I order Another BCU

I will add the codes of the bcu tomorrow

sorry for the long post

Thanks for reading

sierrafery · Mar 25, 2023

The BCUs are fully programmable, doesnt matter what year the vehicle was made but it's not just plug and play programming is needed, the engine will not start untill the engine ECU is set with nanocom or similar to learn the replacement BCU's security code :
· Learn security code: When the ignition is turned on, the BCU or Alarm, providing it is in
receipt of a valid transmitted Key Fob code and is therefore not in an alarmed or
immobilised state sends a coded data transmission to the TD5 ECU. The TD5 ECU then
decodes this data and compares the code contained in it against a mobilization code it
has stored in it. If the two codes compare OK, the TD5 will allow the engine to start.
This forms the basis of the immobiliser. If the TD5 ECU, the BCU, or the Alarm is
changed, it may be required for the TD5 ECU to re-learn a new mobilization code. This is
done by using this function to put the TD5 ECU into Security learn mode. After setting
the TD5 ECU into learn mode it is required to turn off the ignition for 15 seconds, then
back on. Receipt and acceptance of a valid code can be verified by viewing the
'Immobilisation Status' in the 'Other' section.

Henry.adams · Mar 26, 2023

sierrafery said:
The BCUs are fully programmable, doesnt matter what year the vehicle was made but it's not just plug and play programming is needed, the engine will not start untill the engine ECU is set with nanocom or similar to learn the replacement BCU's security code :
· Learn security code: When the ignition is turned on, the BCU or Alarm, providing it is in
receipt of a valid transmitted Key Fob code and is therefore not in an alarmed or
immobilised state sends a coded data transmission to the TD5 ECU. The TD5 ECU then
decodes this data and compares the code contained in it against a mobilization code it
has stored in it. If the two codes compare OK, the TD5 will allow the engine to start.
This forms the basis of the immobiliser. If the TD5 ECU, the BCU, or the Alarm is
changed, it may be required for the TD5 ECU to re-learn a new mobilization code. This is
done by using this function to put the TD5 ECU into Security learn mode. After setting
the TD5 ECU into learn mode it is required to turn off the ignition for 15 seconds, then
back on. Receipt and acceptance of a valid code can be verified by viewing the
'Immobilisation Status' in the 'Other' section.

Yeah I learnt the security codes and set it to manual the immobiliser is off I can hear the fuel pump and it cranks that’s good news then if I don’t need to buy a another bcu someone told me I had to match the codes

sierrafery · Mar 26, 2023

Henry.adams said:
Yeah I learnt the security codes and set it to manual the immobiliser is off

It's some other issue then if it doesnt start, did you purge the fuel with the 5 pedal method? also check the voltage n the battery while cranking, if it drops below 10.5V it will hardly start... any fuel smell at the exhaust while cranking?

Henry.adams · Mar 26, 2023

sierrafery said:
It's some other issue then if it doesnt start, did you purge the fuel with the 5 pedal method? also check the voltage n the battery while cranking, if it drops below 10.5V it will hardly start... any fuel smell at the exhaust while cranking?

I think is most likely the fuel syetem I did Purge it and I could hear air escaping at the Pressure regulator. I pressed the pedal 5 times so the pump would stay on and left it for 10 minutes.

sierrafery · Mar 26, 2023

Henry.adams said:
I think is most likely the fuel syetem I did Purge it and I could hear air escaping at the Pressure regulator. I pressed the pedal 5 times so the pump would stay on and left it for 10 minutes.

that "hiss" you hear is not air even if it sounds so, there's no air release valve there, it's the sound of fluid passing at the diaphragm also it's useless to let it 10 minutes as the purge cycle should end by itself as the ECU cuts the fuel after 3 minues if the engine is not running. You must see the flashing EML on dash while the purge is active, once the EML stopped flashing the pump is disabled too...if this doesnt happen on your's it's a problem with the ECU.

Henry.adams · Mar 26, 2023

sierrafery said:
that "hiss" you hear is not air even if it sounds so, there's no air release valve there, it's the sound of fluid passing at the diaphragm also it's useless to let it 10 minutes as the purge cycle should end by itself as the ECU cuts the fuel after 3 minues if the engine is not running. You must see the flashing EML on dash while the purge is active, once the EML stopped flashing the pump is disabled too...if this doesnt happen on your's it's a problem with the ECU.

Ok mate so I put the ignition on pump the throttle 5 times then the EmL light will start flashing and that’s how I know it’s working ?

sierrafery · Mar 26, 2023

Henry.adams said:
Ok mate so I put the ignition on pump the throttle 5 times then the EmL light will start flashing and that’s how I know it’s working ?

Yes

Henry.adams · Mar 26, 2023

sierrafery said:
Yes

Got it running Purged the fuel and a bit of break cleaner in the intake and it fired up now it starts first turn of the key thanks for the help

TD5 bcu

Henry.adams

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sierrafery

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Henry.adams

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sierrafery

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Henry.adams

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sierrafery

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Henry.adams

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sierrafery

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Henry.adams

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