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How to Replace an Audi etron key G28 Engine Speed Sensor

In this video, Charles the Humble Mechanic demonstrates how to replace the G28 engine speed sensor. This sensor is situated on the outside of the transmission just above the flywheel gear. It transmits a signal the ECU via a grey wire (T55/49) which is then sent to the tachometer within the instrument cluster.

1. Engine Speed Sensor

The grey wire is located on the edge of transmission, just above the flywheel ring. This sensor sends a signal via the grey wire to pin T55/49. The ECU utilizes this information to control the amount of fuel and boost. It also sends an indication to the G5 Tachometer in instrument cluster.

The sensor new Audi keys is used as a reference for comparing with the G40 Camshaft Position Sensor. The ecu needs to know when the crankshaft has reached TDC, and the location of the camshaft to trigger the spark and injectors.

If this sensor fails the ECU will throw an error code P00160 which indicates that the Crank Shaft and Intake Camshaft aren't in sync and could indicate the chain is stretched or a jump link on the upper timing chain. The code won't show without the additional information provided by other sensors (G4 or G40).

It can be a bit difficult to test since there are various pins on the connector, and each has its own functions. The best method for doing this is to measure the resistance between the ECU and the sensor. It should read approximately 1000 ohms if the sensor is at full operation. If you're experiencing issues with this part, check for signs of coolant or oil in the connector Audi Car Key Case bay.

2. Injectors

Yesterday, when i was accelerating to the fullest speed from highway paytoll, i experienced a big cut in power as if the engine was running out of gas or injectors are not firing any more. I took out the spark plugs this morning and found that 3 were drenched in gasoline and the fourth was dry. I put a piece of tissue over each injector hole and when i start the engine with no sparks, the ones that have gazoline pop right out. The 4th one remains shut. I tested the ground connection of ECU pins 14,30, and 48/55. I got 0ohm. I think the issue is somewhere else.

I also tried to reset the PID without success. The car will start when the G28 is unplugged, and it is running fine with the G28 plugged in. However, the intermittent misfire problem persists at higher RPM. The coolant sensor (G62) even when it is unplugged, shows a temperature of -49c. I also noticed that the gauge for oil pressure in the cockpit shows 2 bar when the actual pressure is 0.0 when I crank up the engine.

I'm not sure what to do, but i think i've pretty much completely ruled out all other possibilities. I'm afraid i may have missed something. If anyone has suggestions, please chime in! TIA!

3. Fuel Pump

The fuel pump of the g28 receives a signal from the RPM sensor. The GM-style sender is identical to the G4 and they both work in the 80 100 200, UrS and RS2 cars so you can easily find one at a junkyard or in a local parts store. Test them out to do - just put 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 end of the connector). They should be infinite ohms.

4. ECU

Our 20vt turbo (3B AAN, ABY, and ADU) engines have an ECU that must know the position and speed of the crankshaft to make a decision about timing of the fuel injectors, etc. In order to do this it makes use of a Crank Position Sensor audi A4 key replacement (G4) and an Engine Speed Sensor (G28). If either of these goes wrong, you will receive codes on the diagnostic scanner which can lead to engine shutdown.

A damaged G28 sensor could result in an inaccurate speed counter for your gearbox or a gearbox that shifts faster than normal, and/or a misfire while in the gear. If you experience any of these issues it is most likely that your sensor is going bad and should be replaced. The good thing is that they are very affordable and readily available, especially if you're looking at a Bosch unit which is what we have. Alternately, the GM version of this unit is also a good option.

5. Tachometer

A malfunctioning engine sensor can cause a myriad of issues in your vehicle. It's a vital component of the audi keyless go's transmission because it communicates to the ECU about how fast or slow the car's crankshaft is spinning. If the sensor fails, it can disrupt the performance of the transmission and the rest of the car's components.

The G5 engine speed sensor is situated on the outside of the transmission above the flywheel ring gear and transmits a signal to the ECU at pin T55/49 through an uncolored wire. The ECU is then able to process this signal to control fuel, timig and boost and then sends it on to the G5 tachometer inside the instrument cluster. You can check the sensor for failure by checking continuity between it and the tachometer. You can also check continuity 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 resistance between those points. This is a typical part that is found across the audi replacement key service 80, 100 200, UrS and RS2 range from 1985 MC through the 1997 UrS AAN and 1995 RS2 ADU. Good ones might be availble in wrecking yards.