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 situated at the edge of transmission just above the flywheel gear. It sends a signal to the ECU via the grey wire (T55/49), then to the tachometer located in the instrument cluster.
1. Engine Speed Sensor
The grey wire is situated at the edges of the transmission, above the flywheel ring. This sensor sends signals through the grey wire to pin T55/49. The ECU utilizes this information to control fuel and boost. It also sends an indicator to the G5 Tachometer in instrument cluster.
The sensor is used to link the G40 Camshaft position Sensor. The ecu must know when the crankshaft reached TDC, and the position of the camshaft, so that it can activate the spark and injectors.
If this sensor fails, the ECU will display an error code P00160 which indicates that the Crank Shaft and Intake Camshaft aren't in sync, possibly indicating chain stretch or a jumped 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 is a little tricky to test as there are several pins on the connector and each has its own functions. The best method for doing this is to measure the resistance between the ECU and the sensor. When the sensor is functional, it should read around 1000 ohms. Check for signs of coolant or oil in the connector bay if you have problems with this part.
2. Injectors
Yesterday, while accelerating from 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. Today, i pulled out the spark plugs, three were drenched in gazoline, the fourth one was dry. I put a piece of tissue over each injector hole and when i start the engine with no sparks, the 3 with gazoline jump right out. audi lost key shut. I tested the ground connection of ECU pins 14,30, and 48/55. I found zero ohm. So i assume the problem is somewhere else.
I also tried to reset the PID with no success. The car will start when the G28 is disconnected, but it runs fine with the G28 plugged in. However, the intermittent misfire problem continues to occur at higher RPM. The temperature sensor 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 bars but the actual pressure is zero.
I don't know what to do. I feel like i've pretty much all other possibilities out. I'm afraid i may have missed something. If anyone has any ideas please let me know! TIA!
3. Fuel Pump
The fuel pump in the g28 gets a signal from the RPM sensor. The GM-style transmitter functions similarly to the G4 sender and works on the 80,100,200, UrS, and RS2 vehicles. It is easy to find a spare in a wrecking shop or parts store. It is easy to test them - simply put your DMM into resistance mode and measure the distance between pins 1 and 2 (with the bump at the connector end facing upwards). They must be infinite Ohms.
4. ECU
The ECU of our 20vt turbo (3B AAN ABY) engines needs to know both the speed and position of the crankshaft to make decisions regarding 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 you have a problem with either of these sensors, the diagnostic scanner will display the codes that could trigger the engine shutting down.
Some of the signs of a failing G28 sensor are an inaccurate gearbox rev counter and gears that shift faster than normal, and/or a misfire when in gear. If you are experiencing any of these issues it is likely that your sensor is failing and needs replacing. The good news is that they are very cheap and easily accessible particularly if you're looking at a Bosch model, which is what ours are. Alternately, GM's version this part is an option.
5. Tachometer
A failing engine sensor could cause a number of problems within your vehicle. It is an important part of the transmission in your Audi, as it transmits information to the ECU on how fast or slow the engine of the car is turning. If audi lost key replacement fails, it will disrupt the performance of the transmission, as well as the rest of the car's components.
The G5 engine sensor is located at the outskirts of transmission, above the flywheel ring. It sends signals via an uncolored wire to the ECU pin T55/49. The ECU then processes this signal to control fuel, timig and boost and then sends it on to the G5 Tachometer located in the instrument cluster. You can test for sensor failure by examining the continuity from the sensor to the tachometer. Also, you can verify continuity between pin T55/49 of the ECU and pin T6a/1 of the instrument cluster (trace [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 part across the Audi 80 100, 200, UrS and RS2 range from 1985 MC until the 1997 UrS AAN and 1995 RS2 ADU, so the best parts could be found in wrecking yards.