How to Replace an Audi G28 Engine Speed Sensor

In this video, Charles the humble mechanic demonstrates how to replace the G28 engine speed sensor. The sensor is situated near the edges of the transmission just above the flywheel ring gear. It transmits a signal to the ECU via an uncolored wire T55/49, then to the tachometer located on the instrument cluster.

1. Engine Speed Sensor

The grey wire is situated on the outside of the transmission, just above the flywheel ring. The sensor transmits an electrical signal through the grey wire to pin T55/49. The ECU uses this information to regulate boost and fuel. It also sends an indication to the G5 Tachometer in instrument cluster.

The sensor is used to connect the G40 Camshaft position Sensor. The ecu must know when the crankshaft reached TDC and also where the camshaft lies in order to activate the spark and injectors.

If this sensor fails, the ECU will display a P00160 code which means the Crank Shaft and Intake Camshaft aren't in sync, possibly indicating chain stretch or a jumped link on the upper chain of timing. The code will not appear without the additional information supplied by other sensors (G4 or G40).

It can be a bit difficult to test since there are different connector pins, and they all have different functions. The most effective method to test it is to measure the resistance between the ECU and the sensor. When the sensor is fully functional, it should read approximately 1000 ohms. Check for evidence of coolant or oil in the connector bay if there are issues with this part.

2. Injectors

Yesterday, while accelerating at full speed from the highway paytoll, I experienced a big cut in power like the engine is out of gas or injectors are not firing any more. I pulled out the spark plugs this morning, 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 on ECU pins 14/55, 30/55 and 48/55. I get 0ohm. I think the issue is elsewhere.

I also tried to reset the PID but with no luck. The car will start when the G28 is disconnected, but it runs fine with the G28 plugged in. However the intermittent misfire issue persists at higher RPM. The coolant temperature sensor (G62) shows the wrong temp value that is -49c even after unplugging it. I also noticed that the oil gauge in the cockpit shows 2 bars while the actual pressure is 0.

I'm not certain what to do, but i feel i have pretty much completely ruled out all other possibilities. I'm worried more info that i might have missed something. Please let me know should you have any suggestions! TIA!

3. Fuel Pump

The fuel pump in the g28 can be activated by a signal sent by the RPM sensor. The GM-style transmitter is identical to the G4 sender and works on the 80,100,200, UrS, and RS2 vehicles. You can easily locate an extra in a wrecking shop or a parts store. Testing them is easy by putting your DMM in resistance mode and measure between pins 1 (with the bump on the connector's end up) and 2 (2nd from left on the black connector's end). They should be infinite ohms.

4. ECU

The ECU of our 20vt turbo (3B AAN ABY ADU) engines must be aware of the position and speed of the crankshaft to make decisions regarding timing of the fuel injector, etc. To do this, it makes use of a Crank Position Sensor (G4) and an Engine Speed Sensor (G28). If either of these sensors go badly, you will see codes on the diagnostic scanner which can cause the engine to shut down.

A failing G28 sensor can cause an inaccurate gearbox speed counter, a gearbox that shifts faster than normal, and/or a misfire in the gear. It is probable that the sensor here is failing and needs to be replaced if you notice any of these signs. They're inexpensive and easy to locate especially in the case of an Bosch unit like ours. Alternatively, GM's version of this part would be an option.

5. Tachometer

A failing engine sensor could cause a number of problems in your vehicle. It is an important part of the transmission of your Audi since it sends information to replace audi key the ECU about how fast or slowly the car's engine is turning. This sensor could cause the transmission to malfunction and other car components to be affected.

The G5 engine speed sensor is located on the outside of the transmission, above the flywheel ring gear and sends a signal to the ECU at pin T55/49, via an uncolored wire. The ECU is then able to process this signal to regulate here fuel, timig and boost as well as transmitting it to the G5 Tachometer located in the instrument cluster. You can test 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 [79trace [79]) and between pin T6a/1 and the instrument cluster pin T26a/12. You should observe around 1000 ohms here of resistance between those two pins. This is a typical part across the Audi 80, 100, 200, UrS and RS2 range from 1985 MC through the 1997 UrS AAN and 1995 RS2 ADU so good parts could be found in wrecking yards.