How to Replace an audi a3 key G28 Engine Speed Sensor

In this video Charles the humble mechanic demonstrates how to replace the G28 engine speed sensor. This sensor is located on the edge of the transmission just above the flywheel ring gear. It transmits a signal to the ECU through the grey wire T55/49 and then to the tachometer on the instrument cluster.

1. Engine Speed Sensor

Located on the edge of the transmission just above the flywheel ring gear the G28 Engine Speed Sensor sends signals to ECU pin T55/49 using an uncolored wire. The ECU uses this information to control the amount of fuel and boost. It also sends an indicator to the G5 Tachometer in instrument cluster.

The sensor is used to correlate the G40 Camshaft position Sensor. The ecu must know when the crankshaft reached TDC, and the location of the camshaft to trigger the spark and injectors.

If this sensor fails, the ECU will display a P00160 code which means the Crank Shaft and Intake Camshaft are out of sync and possibly indicating chain stretch or a jumped link on the upper timing chain. However, the code won't be displayed on its own without additional information from other sensors (G4 and G40).

Testing is a bit challenging because there are two connector pins and they perform different functions however the best method of testing it is by measuring resistance between the sensor and the ECU. It should read around 1000 ohms when the sensor is operating at its maximum. If you're experiencing issues with this component, look for signs of coolant or oil in the connector bay.

2. Injectors

Yesterday, while accelerating at full speed from the highway paytoll, I experienced massive power loss like the engine is out of gas or the injectors are not firing at all. I took out the spark plugs this morning, three were soaked in gasoline, and the fourth was unclean. I placed a tissue over each hole in the injector and when i turn the engine on without sparks, the ones with gazoline jump right out. The fourth one remains closed. I checked the ground connection of ECU pins 14,30 and 48/55. I got zero ohm. I'm assuming that the issue is elsewhere.

I also tried to reset the PID but with no luck. The car is able to start if the G28 is disconnected and runs fine when it is connected however it has the intermittent misfire issue at higher RPM. The temperature sensor for the coolant (G62) shows the wrong temperature value of -49c, even if I unplug it. I also noticed that the oil gauge in the cockpit shows 2 bar when the actual pressure is 0.

I'm not sure what to do, but i believe that i've ruled out everything else. But i am afraid i might have missed something. If anyone has suggestions, please chime in! TIA!

3. Fuel Pump

The fuel pump on the g28 is activated by a signal by the RPM sensor. The GM-style transmitter is identical to the G4 sender and both work 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 the resistance between pins 1 (with the bump on the connector's end up) and 2 (2nd from the left on the black connector's side). They should be infinite Ohms.

4. ECU

Our 20vt turbo (3B AAN, ABY, and ADU) engines have an ECU that needs to be aware of the speed and position of the crankshaft to make decisions about timing of the fuel injectors, etc. To accomplish this, it makes use of a Crank Position Sensor (G4) and an Engine Speed Sensor (G28). If either of these sensors go bad you will get codes on the diagnostic scanner which can cause the engine to shut down.

A malfunctioning G28 sensor could result in an inaccurate speed counter for the gearbox or a gearbox that shifts more quickly than normal, or a misfire while in the gear. It is likely 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 cheap and readily available, especially in the case of a Bosch model, like ours. Alternatively, GM's version of this part is an option.

5. Tachometer

A malfunctioning engine sensor can cause a variety of issues in your car. It is an important part of the transmission of your audi a3 key because it relays information to the ECU on how fast or slowly the engine of the car is turning. This sensor could cause the transmission to malfunction and other components in the car to be affected.

The G5 engine sensor is located at the edge of the transmission, just above the flywheel ring. It transmits an electrical signal through gray wire to ECU pin T55/49. The ECU then processes the signal to control the flow of fuel, timig and boost, and also sends it on to the G5 tachometer inside the instrument cluster. You can test for sensor Audi Key Blade failure by examining the 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 [79trace [79]) and between pin T6a/1 and pin T26a/12. You should see the resistance to be around 1000 ohms between these points. This is the same across the audi advance key 80-100-200-RS2 model, ranging from the 1985 MC up to the 1997 UrS AN and the 1995 RS2 DU, so you might find good ones in wrecking yards.