How to Replace an Audi G28 Engine Speed Sensor
Charles the Humble Technician teaches you how to replace the G28 Engine Speed Sensor. This sensor is located near the edges of the transmission, above the flywheel ring gear. It sends a message to the ECU through the grey wire T55/49 and then to the tachometer on the instrument cluster.
1. Engine Speed Sensor
The grey wire is situated at the edges of the transmission, just above the flywheel ring. This sensor sends an electrical signal through the grey wire to pin T55/49. The ECU then utilizes this information to regulate the boost, fuel, and timig. It also sends an indication to the G5 Tachometer in instrument cluster.
The sensor is used as a reference for comparing with the G40 Camshaft Position Sensor. The ecu needs to be aware of when the crankshaft has reached TDC and also where the camshaft lies to trigger the spark and injectors.
If this sensor fails, the ECU will display a P00160 error code. This indicates that the Crank Shaft is out of sync with the Intake Camshaft. It could also indicate a chain stretch or a jumpy chain link in the upper chain. However, the error code won't appear on its own without additional information from other sensors (G4 and G40).
It is a little tricky to test as there are several pins on the connector, and each one has different functions. The best way to do it is to measure the resistance between the ECU and the sensor. If the sensor is functional, it should read about 1000 ohms. If you are having problems with this part, check for evidence of coolant or oil in the connector bay.
2. Injectors
Yesterday accelerating full speed from highway paytoll, I experienced a big cut in power as if the engine was running out of gas or the injectors are not firing at all. Today, i pulled out the spark plugs. Three were drenched with gazoline the fourth one was dry. When i crank the engine with no sparks i put tissue on the top of each hole in the injector and the 3 drenched with gazoline jump out but the 4th one stays closed. I inspected the ground connection on ECU pins 14/55/30/55/48/55/14/55/48/ i get 0ohm. I assume that the problem is somewhere else.
I also tried to reset the PID without success. The car will start if the G28 is unplugged and it runs perfectly when it is connected but it still has intermittent misfire issues at higher RPM. The temperature sensor for coolant (G62) shows the wrong temperature of -49c even when i unplug it. I also noticed that the oil gauge in the cockpit shows 2 bars when the actual pressure is zero.
I don't know what to do. I feel like i've pretty much ruled everything else out. I'm worried that i might have missed something. Please let me know if you have any ideas! TIA!
3. Fuel Pump
The fuel pump of the g28 gets a signal from the RPM sensor. The GM-style transmitter is similar to the G4 sender, and both operate on the 80,100,200, UrS, and RS2 vehicles. It is easy to find an extra in a wrecking shop or a parts store. Test them out by putting your DMM in resistance mode and take measurements between pins 1 (with the bump on the connector's end up) and 2 (2nd from left on the black connector's side). They must be infinite Ohms.
4. ECU
Our 20vt turbo (3B AAN, ABY and ADU) engines are equipped with an ECU that has to be aware of the speed and position of the crankshaft in order to make decisions regarding timing of the fuel injector, for example. To do this, it uses a Crank Position Sensor (G4) and an Engine Speed Sensor ( G28 ). If you encounter a problem with either of these, the diagnostic scanner will display the codes that could trigger an engine shut down.
The signs of a failing G28 sensor are an inaccurate gearbox rev counter, gears shifting quicker than normal and/or misfiring when in gear. It is probable that the sensor is failing and requires to be replaced if you notice any of these signs. The good thing is that they are very affordable and easy to find particularly if you're looking at an Bosch unit which is what we have. Alternatively, the GM version of this unit is also a good choice.

5. Tachometer
A faulty engine speed sensor could be the reason behind many problems in your vehicle. It's an essential component of your Audi's transmission, because it communicates to the ECU about how fast or slow the vehicle's crankshaft is spinning. This sensor can cause the transmission to fail and other components in the car to be affected.
The G5 engine sensor is located at the outskirts of the transmission, just above the flywheel ring. It sends an electrical signal through gray wire to ECU pin T55/49. The ECU utilizes this signal to regulate fuel and boost, as well as timig. It also relays it to the G5 Tachometer inside the instrument cluster. You can check the sensor for any failure by checking the continuity between it and the tachometer, between ECU pin T55/49 and the instrument cluster connection to pin T6a/1 (trace [79]) and between T6a/1 and the instrument cluster pin T26a/12. You should observe approximately 1000 ohms of resistance between those points. This part is common across the Audi 80-100-200-RS2 model, ranging from the 1985 MC up to the 1997 UrS AN and 1995 RS2 Du, so you might find good ones in wrecking yards.