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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 over the flywheel gear. It sends a signal to 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, above the flywheel ring gear, the G28 Engine Speed Sensor sends a signal to ECU pin T55/49 through an uncolored wire. The ECU then uses this information to control the flow of fuel, timig and boost. It also sends signals to the G5 Tachometer located in the instrument cluster. The sensor is used as a reference point to connect with the G40 Camshaft Position Sensor. The ecu needs to know when the crankshaft is TDC and where the camshaft is located so that it can trigger spark and injectors accordingly. If this sensor fails, the ECU will display a P00160 error message. This indicates that the Crank Shaft is not in alignment with the Intake Camshaft. It could also indicate the possibility of a chain stretch or jump in the chain link of the upper chain. However, the code won't appear on its own, without additional information from other sensors (G4 and G40). Testing is a bit tricky since there are two connector pins, and they have different functions however the best method of testing it is to measure the resistance between the sensor and the ECU. If the sensor is operational, it should read about 1000 ohms. If you are having problems with this component, look for signs of oil or coolant in the connector bay. 2. Injectors Yesterday accelerating full speed from highway paytoll, I experienced a big cut in power like the engine is out of gas or the injectors aren't firing any more. This morning i pull out the spark plugs. Three were drenched with gazoline the fourth one was dry. When i crank the engine without sparks, I put a piece of tissue on the top of each hole in the injector and the 3 that were drenched in gazoline jump out but the 4th stays shut. I tested the ground connection on ECU pins 14/55, 30/55 and 48/55. I get 0ohm. So i assume the problem is somewhere else. I also tried to reset the PID without success. The car is able to start when the G28 is unplugged and it runs perfectly when it is plugged in, but still has the intermittent misfire issue at higher RPM. audi a3 key replacement for the coolant (G62) shows the wrong temp value -49c even when i unplug it. I also noticed that the oil gauge in the cockpit shows 2 bar when the actual pressure is zero. I don't know what to do. I feel like i've pretty much eliminated 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 of the g28 gets a signal from the RPM sensor. The GM-style transmitter is identical to the G4 and both are used in the 80 100 200, UrS and RS2 cars so you can easily find one at a salvage yard or at a parts store. It is easy to test them: simply switch your DMM into resistance mode and test the distance between pins 1 and 2 (with the bump at the connector end facing up). They must be infinite Ohms. 4. ECU Our 20vt turbo (3B AAN, ABY, and ADU) engines are equipped with an ECU that has to know the position and speed of the crankshaft to make decisions about fuel injector timing etc. It makes use of a Crank Position Sensor G4 and an Engine Speed Sensor G28 to accomplish this. If either of these go bad you will get codes on the diagnostic scanner that can lead to engine shutdown. A malfunctioning G28 sensor could result in an inaccurate speed counter for your gearbox and a gearbox which shifts more quickly than normal, and/or an unfire when in the gear. If you are experiencing any of these issues, it is likely that your sensor is going bad and requires replacement. They are cheap and easy-to-find especially in the case of a Bosch model like ours. You can also choose the GM version of this unit is also a good option. 5. Tachometer A damaged engine sensor could cause a number of problems in your vehicle. It's an essential component of the transmission of your Audi, as it transmits information to the ECU regarding how fast or slowly the engine is turning. This sensor can cause the transmission to fail and other components in the car to be affected. The G5 engine speed sensor is located on the edge of the transmission above the flywheel ring gear. It sends a signal directly to the ECU at pin T55/49, via a grey wire. The ECU then processes the signal to control fuel, timig and boost as well as sends it on to the G5 tachometer inside the instrument cluster. You can determine if the sensor is in failure by examining the continuity of the sensor to the tachometer. Additionally, 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 those two pins. This is a typical component across the Audi 80, 100, 200, UrS and RS2 range from 1985 MC to the 1997 UrS AAN and 1995 RS2 ADU so good ones might be availble in wrecking yards.