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How to Replace an Audi G28 Engine Speed Sensor Charles the Humble Technician shows how to replace the G28 Engine Speed Sensor. This sensor is located on the outside of the transmission, above the flywheel gear. It transmits a signal the ECU via a grey wire (T55/49) and then to the tachometer in the instrument cluster. 1. Engine Speed Sensor Located on the edge of the transmission just above the flywheel ring gear G28 Engine Speed Sensor sends an electrical signal to ECU pin T55/49 using an uncolored wire. 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 as a reference to correlate with the G40 Camshaft Position Sensor. The ecu must be aware when the crankshaft is TDC and where the camshaft is located so that it can activate spark and injectors in the right way. If this sensor fails, the ECU will display the P00160 error, which means the Crank Shaft and Intake Camshaft aren't in sync and could indicate the chain stretching or a jump link on the upper timing chain. However the code will not appear on its own without additional information from other sensors (G4 and G40). It can be a bit difficult to test because there are several connector pins, and each one has different functions. The best way to do it is to measure the resistance between the ECU and the sensor. It should read about 1000 ohms when it is operating at its maximum. Check for signs of coolant or oil in the connector bay if you have problems with this part. 2. Injectors Yesterday, as i was accelerating off the highway paytoll at maximum speed, i noticed a huge drop in power. It was like the engine had run out of gas. Or, my injectors weren't firing. I took out the spark plugs this morning, three were soaked with gasoline and the fourth was unclean. I placed a tissue over each injector hole, and when i turn the engine on without sparks, the three with gazoline jump out. The 4th one stays closed. I checked the ground connection on ECU pins 14/55,30/55 and 48/55 I get zero ohm. I assume that the problem is elsewhere. I also tried to reset PID but 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 unplugged, still shows temperatures of -49c. Also audi spare keys noticed that the oil pressure gauge in the cockpit is showing 2 bar while the actual pressure is 0.0 when I crank up the engine. I'm not sure what to do, but i feel i have pretty much completely ruled out all other possibilities. I'm afraid i may have missed something. If anyone has any suggestions, please chime in! 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 similar to the G4 sender, and both operate on the 80,100,200, UrS, and RS2 vehicles. You can easily find the spare in a salvage shop or parts store. It is simple to test them – simply put your DMM into resistance mode and test the distance between pins 1 and 2 (with the bump at the connector end facing up). They should 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. It utilizes a Crank Position Sensor G4 and an Engine Speed Sensor G28 to achieve this. If you are experiencing issues with either of these sensors, the diagnostic scanner will show codes that could cause an engine shutdown. Some of the symptoms of a failing G28 sensor are an inaccurate rev counter in the gearbox, gears shifting quicker than normal, and/or a misfire when you are in gear. If you are experiencing any of these problems, it is most likely that your sensor is deteriorating and requires replacement. They're cheap and easy to find especially if they're a Bosch sensor like ours. You can also choose the GM version of this part is also a good choice. 5. Tachometer A malfunctioning engine sensor can cause a myriad of issues in your vehicle. It is a crucial part of the Audi's transmission as it sends information to the ECU about how fast or slow the vehicle's crankshaft is spinning. If this sensor fails, it can cause problems for the transmission and the other car's components. The G5 engine speed sensor is situated on the outside of the transmission above the flywheel ring gear. It sends a signal to the ECU at pin T55/49 through a grey wire. The ECU is then able to process the signal to control fuel, timig and boost, and also transmitting it to the G5 tachometer inside the instrument cluster. You can test the sensor for failure by examining the continuity between it and the tachometer, between the ECU pin T55/49 and the instrument cluster connection to pin T6a/1 (trace [79trace [79]) as well as between T6a/1, and the instrument cluster pin T26a/12. You should see approximately 1000 ohms of resistance between those points. This is a typical 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. Good parts could be found in wrecking yards.