Earthed Throttle position Sensor

[blue95 0]

Hello all,

Whilst sorting my replacement engine harness (95 VR6) i noticed on my old loom that the wiring for my Throttle position Sensor had been altered, in particular the brown/green wire had been earthed....just wondered why this would need to be done? as the wiring looked OK, assume the the other end is earthed somewhere

Edited September 29, 2020 by blue95

[fendervg 29]

Sounds strange - I would have thought the TPS was variable resistance, so one wire is + and the other -, with the ECU interpreting the difference - surely a separate earth straight to ground would mess this up? Do you have any pictures?

Or could it be that your previous loom was for a motorised throttle on OBD2, maybe a AAA engine transplant from a Golf?

Edited September 29, 2020 by fendervg

[blue95 0]

Green/White - Throttle Position Sensor Signal?
Black/Gray - Throttle Position Sensor Power?
Brown/Green - earth

Plan to trace the Brown/Green wire to see where it goes to originally as well - can only assume root cause was bad earth but id like to be sure.  Dont plan to emulate on my newer loom

Edited September 29, 2020 by blue95

[tonedef 8]

If you look at the following pinout for the OBD1 VR6 ECU you'll see these allocations:

Pin 40 TPS signal 1 Green/White

Pin 41 TPS Power Black/Grey

Pin 33 Sensors Ground (including Throttle) Brown

Click

I also have a Golf wiring diagram which shows the same wiring,:

TPS pin 1 to plug T42 pin 28 Brown/Green which joins a group of other Brown/(Second Colour) wires before becoming finally a brown which goes to ECU plug T68 pin 33 

TPS Pin 2 to plug T42 pin 29 Green/White to ECU plug T68 pin 40

TPS pin 3 to plug T42 pin 34 Black/Grey to ECU plug T68 pin 41

Admittedly it's not a Corrado diagram but I've swapped enough looms around to know they generally follow, it suggests your wiring whilst maybe not the neatest is correct as installed.

Edited September 29, 2020 by tonedef

[blue95 0]

Cheers, traced the wire back goes to the multiplug, the old loom did have a few cracks and the wire was corroded, so assume there was a bad earth at some point which led to this fix.

[fendervg 29]

10 hours ago, tonedef said:

If you look at the following pinout for the OBD1 VR6 ECU you'll see these allocations:

Pin 40 TPS signal 1 Green/White

Pin 41 TPS Power Black/Grey

Pin 33 Sensors Ground (including Throttle) Brown

Click

I also have a Golf wiring diagram which shows the same wiring,:

TPS pin 1 to plug T42 pin 28 Brown/Green which joins a group of other Brown/(Second Colour) wires before becoming finally a brown which goes to ECU plug T68 pin 33 

TPS Pin 2 to plug T42 pin 29 Green/White to ECU plug T68 pin 40

TPS pin 3 to plug T42 pin 34 Black/Grey to ECU plug T68 pin 41

Admittedly it's not a Corrado diagram but I've swapped enough looms around to know they generally follow, it suggests your wiring whilst maybe not the neatest is correct as installed.

Ah ok - so it's 3 wires at the TPS plug then - serves me right for being too lazy to open the bonnet in the rain the check! Looks like it was just a workaround for a bad earth then, to avoid having to inspect the whole loom and fix.