How to Replace an audi tt key G28 Engine Speed Sensor

Charles the Humble Technician shows how to replace the G28 Engine Speed Sensor. This sensor is located near the transmission's edge over the flywheel gear. It transmits a signal to the ECU via the grey wire T55/49 and then to the tachometer on the instrument cluster.

1. Engine Speed Sensor

It is located on the outside of the transmission above the flywheel ring gear, the G28 Engine Speed Sensor sends signals to ECU pin T55/49 via the grey wire. The ECU then utilizes this information to regulate fuel, timig and boost. It also sends an indicator to the G5 Tachometer located in the instrument cluster.

The sensor is used to correlate the G40 Camshaft position Sensor. The ecu must know when the crankshaft is TDC and the location of the camshaft so it can activate spark and injectors in the right way.

If this sensor fails when it fails, the ECU will display an error code P00160. This indicates that the Crank Shaft is out of line with the Intake Camshaft. It could also indicate the possibility of a chain stretch or jump in the chain link of the upper timing chain. However, the error code won't be displayed on its own without additional information from other sensors (G4 and G40).

It can be a bit difficult to test since there are several pins on the connector, and they all have different functions. The best method for doing this is to measure the resistance between the ECU and the sensor. It should read approximately 1000 ohms when it is at full operation. If you're experiencing issues with this part, check for signs of coolant or oil in the connector bay.

2. Injectors

Yesterday, as i was accelerating off the highway paytoll at full speed, i noticed a huge drop in power. It was like the engine had run out of gas. Or, my injectors were not firing. I took out the spark plugs this morning and found that 3 were drenched in gasoline and the fourth was unclean. I put tissue over each hole in the injector and when I start the engine without sparks, the ones that have gazoline pop right out. The 4th one stays closed. I tested the ground connection on ECU pins 14/55, 30/55 and 48/55. I get 0ohm. Therefore, i think the issue is elsewhere.

I also tried to reset the PID without success. The car will start when the G28 is disconnected, but it works fine when the G28 connected. However, the intermittent misfire problem still occurs at higher RPM. The temperature sensor for 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 bar when the actual pressure is 0.

I'm not certain what to do, as i think i've pretty much ruled out everything else. I'm afraid i may have missed something. Let me know if you have any ideas! TIA!

3. Fuel Pump

The fuel pump in the g28 gets a signal from the RPM sensor. The GM-style transmitter is the same as 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 at a parts store. Testing them is easy 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 end). They must be infinite Ohms.

4. ECU

The ECU in our 20vt turbo (3B AAN ABY) engines requires to know the position and speed the crankshaft in order to make a decision about fuel injector timing, etc. In order to do this it makes use of a Crank Position Sensor (G4) and an Engine Speed Sensor (G28). If either of these sensors go wrong, you will receive codes on the diagnostic scanner which could cause engine shut down.

Some of the symptoms of a failed G28 sensor are an inaccurate rev counter for the gearbox the gears are shifting faster than normal and/or a misfire when you are in gear. If you have any of these issues, it is most likely that your sensor is going bad and requires replacement. The good news is that they are very cheap and readily available, especially in the case of the Bosch sensor, like ours. You can also choose the GM version of this unit is also a great option.

5. Tachometer

A failing engine sensor could cause a number of problems in your vehicle. It is a crucial part of your audi keyless entry's transmission, since it relays information to the ECU about how fast or slow the vehicle's crankshaft is rotating. If 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 on the edge of the transmission, above the flywheel ring gear. It transmits a signal to the ECU at pin T55/49 via an uncolored wire. The ECU then processes this signal to control the flow of fuel, timig and boost as well as transmitting it to the G5 tachometer inside the instrument cluster. You can check for sensor failure by checking continuity from the sensor to the tachometer. You can also examine the continuity between pins T55/49 of the ECU and pin T6a/1 of the instrument cluster (trace [79]) and between pin T6a/1 and pin T26a/12. You should observe around 1000 ohms of resistance between those two pins. This part is common across the audi spare keys 80-100-200-RS2 range, beginning with the 1985 MC and up to the 1997 UrS AN and 1995 RS2 Du You may also find some good ones in wrecking yards.