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Updated the 2007 version of my AAN pin-out in Post 1 in this thread to the current version I have at my home forum, quattroworld. With photos and hyperlinks to the connected devices, etc. etc.
While wire colours might not cross to the ABY and ADU the pins are the same and info about the connected devices applies equally well.
I had to go to my Connector Stn 2 post to confirm that the T6a is green and the T6c is red and its the T6c that carries the speedometer signal and T6a the tachometer signal.
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If AAN car - it is brown/red through T6c Red pin 1.
I think you have the Speedometer and Tachometer confused (maybe the English/German translation?). What you say is correct for the speedometer, not the tachometer (rev counter).
The G28 Engine Speed Sensor on the edge of transmission, above the flywheel ring gear, sends its signal to T55/49 on the ECU in a Grey wire. The ECU uses and processes this signal appropriately to control fuel, timig and boost. It also sends a signal to the G5 tachometer in the instrument cluster. This G5 signal leaves the ECU on pin T55/40 (trace [79]) as a violet/black wire, goes through a T6a connector (as Pin T6a/1) (a green 6 pin connector in Connector Station 2 (passenger kick panel)) and emerges as a green wire (trace [79]). This green wire enters the C4 UrS instrument cluster on trace [174] and instrument cluster pin T26a/12.
If you have tachometer problems on your UrS, make sure that you have continuity between the G28 and the T55/49 ECU pin and between the T55/40 ECU pin, the T6a/1 connection and the T26a/12. If those show up good, you might have problem on the instrument cluster printed circuit board (cold joint/cracked trace that is often fixable).
BTW, the [578] destination on the [80] trace is the Automatic Climate Control head, i.e. the reason you can read the RPM on Channel 28 of the Climate Control Diagnostics
What can be the cause when the ECU sees engine speed, Vag Com shows RPM but the instrument cluster not? We tried 2 different clusters but still no RPM. What cable goes from the ECU to the cluster?
The G28 engine speed sensor signal enters the ECU on pin 49 as a blue wire:
EDIT: It goes through the ECU, is utilized as needed, and a signal to the G5 Tachometer emerges on Pin T55/40 as lilac (violet/purple) wire and as _ShurikeN noted, first going through a T10 connector on pin T10/7. It emerges from the T10 as green/blue wire and heads to the instrument cluster at pin T26/22. You need to check for continuity, broken wires and/or corrosion in the connectors, e.g. the T10.
Diagrams found in the Technical section of S2Central.net
Updated AAN Motronic ECU device list and T55 pin-out
Originally posted by caterpillar
really nice info...!!!
Wow. That must have been one of the earliest posts I made here in 2007. I have moved well beyond that point. Here is the latest version of that T55 AAN ECU connector pin-out (with hyperlinks to info about each of the devices to which the ECU is connected):
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What can be the cause when the ECU sees engine speed, Vag Com shows RPM but the instrument cluster not? We tried 2 different clusters but still no RPM. What cable goes from the ECU to the cluster?
What car?
If S2 - look for green/blue cable, going from engine loom to dash loom through black connector T10 pin 7.
If AAN car - it is brown/red through T6c Red pin 1.
What can be the cause when the ECU sees engine speed, Vag Com shows RPM but the instrument cluster not? We tried 2 different clusters but still no RPM. What cable goes from the ECU to the cluster?
6-Connection to A/C Control Head –E87- G/Y –Used to shut off A/C for up to 12 seconds when throttle is opened rapidly at speeds under 7 kph and shut off A/C for up to 3 seconds when in first gear and throttle position is at 65 degrees or more (full load) Ref: VAG143.
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