User description

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, above the flywheel ring gear. It transmits a signal the ECU via an uncolored wire (T55/49) which is then sent to the tachometer in the instrument cluster.

1. Engine Speed Sensor

The grey wire is situated on the outside of the transmission, just above the flywheel ring. This sensor sends signals through the grey wire to pin T55/49. The ECU then uses this information to control the flow of fuel, timig and boost. It also sends an indication to the G5 tachometer in the instrument cluster.

The sensor is used to link with the G40 Camshaft position Sensor. The ecu needs to know when the crankshaft reached TDC and also the position of the camshaft, so that it can activate the spark and injectors.

If this sensor fails, the ECU will display a P00160 error message. This indicates that the Crank Shaft is out of alignment with the Intake Camshaft. It could also indicate a chain stretch or a jumped chain link in the upper chain. The code won't appear without the additional information supplied by other sensors (G4 or G40).

Testing can be a bit difficult as there are two different pins for the connector and they perform different functions however the best method to test it is to measure the resistance between the sensor and the ECU. When the sensor is fully operational, it should be reading about 1000 ohms. If you're experiencing issues with this part, check for evidence of oil or coolant in the connector bay.

2. Injectors

Yesterday, when i was accelerating to the fullest speed from highway paytoll, i experienced a big cut in power like the engine is out of gas or the injectors aren't firing at all. I pulled out the spark plugs this morning, 3 were soaked in gasoline, and the fourth was dry. When I crank the engine with no sparks i put tissue on the top of each hole in the injector, the 3 drenched with gazoline leap out, however the 4th one stays closed. I tested the ground connection on ECU pins 14/55/30/55/48/55/14/55/48/ i get zero ohm. I assume that the problem is somewhere else.


I also tried to reset PID without success. The car can start if the G28 is not plugged in and is running fine when it is plugged in however it is experiencing intermittent misfires at higher RPM. The temperature sensor for the coolant (G62) shows the wrong temperature value of that is -49c even after unplugging it. I also noticed that the oil gauge in the cockpit shows 2 bars when the actual pressure is 0.

I'm not certain what to do, i think i've pretty much ruled out everything else. But i am afraid i might have missed something. Please let me know If you have any suggestions! TIA!

3. Fuel Pump

The fuel pump in the g28 receives a signal from the RPM sensor. The GM-style transmitter is similar to the G4 sender and both work on the 80,100,200, UrS, and RS2 vehicles. You can easily locate a spare in a wrecking shop or a parts store. It is simple to test them - put your DMM in resistance mode and measure the resistance between pins 1 (with the bump on the connector's side up) and 2 (2nd from the left on the black connector's end). They should be infinite ohms.

4. ECU

The ECU in our 20vt turbo (3B AAN ABY ADU) engines must know the position and speed of the crankshaft to determine fuel injector timing, etc. In order to do this it uses a Crank Position Sensor (G4) and an Engine Speed Sensor (G28). If either of these goes bad you will get codes on the diagnostic scanner which can lead to engine shutdown.

A damaged G28 sensor can cause an inaccurate gearbox speed counter, a gearbox that shifts faster than normal, or an unfire when in gear. If you are experiencing any of these issues it is most likely that your sensor is deteriorating and requires replacement. The good thing is that they are very affordable and readily available, especially in the case of an Bosch unit which is what we have. Alternatively, GM's version of this part would be a good option.

5. Tachometer

A failing engine speed sensor could be the cause of a slew of issues in your vehicle. more information is a crucial part of the Audi's transmission since it relays information to the ECU about how fast or slow the vehicle's crankshaft is rotating. When this sensor fails, it can cause problems for the transmission and the rest of the car's components.

The G5 engine speed sensor is located at the edge of the transmission above the flywheel ring gear. It transmits a signal to the ECU at pin T55/49 through an uncolored wire. The ECU then uses and processes this signal to control fuel, timig and boost as well as transmitting it to the G5 Tachometer located in the instrument cluster. You can check for sensor failure by examining the continuity from the sensor to the tachometer. Also, you can check continuity between pin T55/49 of the ECU and pin T6a/1 of the instrument cluster (trace [79trace [79]) and between pin T6a/1 as well as pin T26a/12. You should observe around 1000 ohms of resistance between these two points. This is a standard part that is found across the Audi 80 100 200, UrS and RS2 range from 1985 MC through the 1997 UrS AAN and 1995 RS2 ADU, so the best ones could be available in wrecking yards.