2010 Audi A5 2.0t Injector Harness Diagram

The UrS fuel injectors are powered through two sources: The J17 Fuel Pump Relay and the ECU via pin 37/55 and a Holding Relay inside the ECU as detailed in this ECU pin-out link and specifically this diagram:

When the ignition key is turned to on, power flows through the ECU (input side is Pin 18/55) via the Holding Relay and out to the injectors and the
G70 Mass Air Flow Sensor via pin 37/55. As the ignition switch is turned to start and the starter is engaged, the ECU starts looking for signals from the G4 Crank Position and G28 Engine Speed sensors and the G40 Cam Position sensor, deciding whether it should trigger the operation of the J17 fuel pump relay.

The ECU does not power the FP relay through pin 3/55 until is gets a good signal from the G4 crank position sensor (via pin T47/55) and the G40 cam position sensor via pin T8/55 (with the G28 engine speed sensor telling the ECU that the engine is turning over at more than 13 RPM (some manuals say 23 RPM). Once the FP relay is powered, the internal connection (in the relay), outputs 12V to the injectors via Pin 87A on the relay. Once the car is running, the ECU continues to check for rotation of the engine via the G4 crankshaft position sensor via pin 47/55. If the engine is ever stopped, e.g. in an accident, the ECU drops the power to the FP relay and the power to the injectors is stopped. This is a safety feature intended to minimize engine fires in an accident.

Now back to the injectors and 87A in the FP relay. The 12V output from 87A leaves the relay via a blue (BL) wire that immediately branches (as blue wire) and goes to two thermo fuses/circuit breakers, S72 and S75. For the UrS6s these are normal fuses. S75 is still S75 but for the UrS6, S72 is S116. With respect to the injectors, we only care about S72/S116. (You will have to worry about S75 and what it powers later).

UrS4 on the left, UrS6 on the right

REFERENCE: ABOVE ECU FUSE CALL OUT POST

The output from S72/S116 leaves S72/S116 as a black wire with a red stripe (BK/R). This wires is branched six times, all as BK/R wires, one each for the five injectors (N30, N31, N32, N33 and N83) and one additional wire that carries on towards pin 37/55 on the ECU. Now comes that part that hopefully will make it all clear: The injectors have a two wire connector, one for power and one for ground. (Here is some info on how the fuel injectors work). They get the 12V power via the red-striped Black wire from 87A via S72 via one of the two injector connector pins. What they still need is a ground that will allow current to flow through the injector, excite the injector solenoid, and open the injector for a precise time period, controlled by the ECU. This electrical ground is provided by the ECU via 5 individual injector wires, routed through the ECU where the ECU controls the fuel injection timing and duration, and then to ground via pin 14/55 on the ECU.

The five injector "ground" wires to the ECU are as follows:

Cylinder 1, Injector N30, connected to Pin36/55 via a white wire with violet (purple) stripe (W/V)
Cylinder 2, Injector N31, connected to Pin 17/55 via a whie wire with a brown stripe (W/BR)
Cylinder 3, Injector N32, connected to Pin 34/55 via a yellow wire with a blue stripe (Y/BL)
Cylinder 4, Injector N33, connected to Pin 35/55 via a yellow wire with a green stripe (Y/G)
Cylinder 5, Injector N83, connector to Pin 16/55 via a white wire with a blue stripe (W/BL)

As a result, when you are testing whether you have voltage at the injectors with the ignition turned on, you do NOT test across the two injector connector harness pins. The problem is that while there might be 12V power on the pin connected to the Black wire with the red stripe, the connector ground, e.g. the white/violet wire on Injector No.1 (front of the engine) is not open via the ECU (yet). Therefore, to check for 12V at the injector, you need to connect one multimeter probe to the pin on the Black/red wire and the other probe to ground, e.g. on the cam cover.

Recently (July 2013), another Holding Relay failure manifested itself, as posted on the S2Forum. The holding relay apparently failed closed, sending power to both Pin 4/6 and Pin 5/6 of the G70 MAF connector even with the engine off. While this was not an issue for Pin 5 (e.g. it left the injectors and MAF energized but the injectors would not do anything without a grounding signal from the ECU, as discussed in this injector wiring post). The big issue was the power to Pin 4/6 which comes from Pin T55/25 in the ECU (via the Holding Relay). This is the power to the hot wire that is intended to stay on for 5 seconds to burn off the crud on the hot wire when the engine is turned off. After the 5 seconds has passed there should be no power coming to the MAF via either Pins 4/6 or 5/6. If the power stays on, it continues to burn the wire (potentially shortening its service life), making the metal portion of the MAF skin-burnable hot and draining the battery. As a result, if you are having strange battery-flattening current draw, check for power at the injectors and/or the MAF at Pins 4 and 5.

UPDATE:

The fuel injectors and a bunch of other devices in the engine bay are connected to the engine harness via a 2 pin (female pin) connector, PN 443906232. This is Item 11 in this engine bay harness diagram (there are a bunch of devices that use this connector):

Recently on the S2Forum, Andy P had issues with a miss on his ABY S2. Naturally we gave him lots of ideas (coils, plugs, connectors, etc etc). Eventually, he fixed his problem by doing a bunch of things at the same time (plugs, better ground(s) and fixing a wiring issue at one (two?) of the injectors. It is likely that the issue was the injector wiring (where did we here *that* one lately)(1gcrazy's miss was based on broken injector wire).

Here is what a hopefully good injector connector (one of mine) looks like (note the purple plastic pin holder):

Here is a shot of one of Andy P's good purple pin holders:

Photo courtesy of Andy P.

Here is a shot of one of Andy P's bad pin holders:

Photo courtesy of Andy P.

Here is another shot of a bad pin holder:

Photo courtesy of Andy P.

It is easy to imagine the possibility of the two wires going to the fuel injectors touching (arching) in one of those bad pin holders, causing a lean mis-fire (not enough fuel in that cylinder).

Andy P replaced the bad pin holders with a new one-piece two pin connector like this one:

Photo courtesy of Andy P.