Common Device Grounds for the AAN ECU's T55/30 pin

[UrS4boy]

This came up on my home forum in response to someone who was getting an "intermittent ground" fault code for the G42 Intake Air Sensor. The G42 has two wires, a brown/blue connected to Pin T55/44 in the ECU and a green/black connected to an ECU ground, along with several other devices the ECU uses or monitors, at pin t55/30. The poster was wondering whether he could just run a new separate ground for the G42. I suggested that there might be issues with that. Other opinions differred. I suggested a continuity check between the green/black wire at the G42 AAN harness connector and pin T55/30. Because I have a spare AAN harness, I was able to check out the continuity I was suggesting is needed as well as open up the T55 connector and look at how the T55 harness handles the multiple wires going to a single T55 pin. The results are shown below. I presume the principle of this will be the same for the ABY and ADU, but the wire colours might be different:

For the AAN, sever wires enter the common crimp located inside the T55 ECU connector. Five of these wires are Green/Black, one is yellow and one is brown. The G42 IAT is one of the green/black wires.

A single green/black wire exits the common crimp and runs to the T55/30 pin.



The seven devices are, left to right,

1. G61 knock sensor, 2. G66 knock sensor, 3. Idle switch/throttle potentiometer, 4. F96 Altitude sensor, 5. G62 engine coolant temp sensor, 6. G42 Intake air temp sensor and 7. Coding card for trip computer (probably regardless of whether the trip computer is installed or not).

[quattro-nick]

Two weeks ago I had the same problem with air temp sensor(AAN engine and wireloom)
the readings in vems were not correctly
After some measuring I come to a conclusion that the ground wire(from g42) was interrupted
so i made an extra ground from the intake to on the green/black wire shortly at the G42 plug and it works well,it gives a correct reading in vems and does not interfere with the other sensors, finally,the green/black wires are all ground
i dont know if i plug the origional AAN ecu motronic on the wireloom what it does with faultycodes on the sensors but that's not relevant on vems so........