How to Replace an Audi G28 Engine Speed Sensor
In this video, Charles the humble mechanic demonstrates how to replace the G28 engine speed sensor. This sensor is located at the edge of transmission, above the flywheel gear. It transmits a signal to the ECU via an uncolored wire (T55/49) which is then sent to the tachometer within the instrument cluster.
1. Engine Speed Sensor
The grey wire is located on the outside of the transmission, above the flywheel ring. The sensor transmits signals through the grey wire to pin T55/49. The ECU then utilizes this information to regulate fuel, timig and boost. It also sends signals to the G5 tachometer in the instrument cluster.
The sensor serves as a reference for comparing 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 start spark and injectors according to the situation.
If this sensor fails the ECU will throw an error code P00160 which indicates that the Crank Shaft and Intake Camshaft aren't in sync, possibly indicating the chain is stretched or a jump link on the upper chain of timing. The code won't show without the additional information provided by other sensors (G4 or G40).
Testing is a bit tricky as there are two different connector pins, and they serve different purposes but the best method to test it is by measuring resistance between the sensor and the ECU. If the sensor is functional, it should read approximately 1000 ohms. Look for signs of coolant, or oil in the connector bay if there are issues with this component.
2. Injectors
Yesterday, when i was accelerating to the fullest speed from highway paytoll, i experienced massive power loss like the engine is out of gas or injectors are not firing anymore. I took out the spark plugs this morning, three were soaked in gasoline, and the fourth was dry. I placed a tissue over each injector hole and when i turn the engine on without sparks, the 3 that have gazoline pop right out. The 4th one remains closed. I tried to test the ground connections of ECU pins 14,30 and 48/55. I found 0ohm. I'm assuming the issue is elsewhere.
I also tried to reset the PID without success. The car will start when the G28 is disconnected, but it runs fine with the G28 plugged in. However, the intermittent misfire problem still occurs at higher RPM. The temperature sensor for 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 0.
I don't know what to do. I think I've eliminated everything else. But i am afraid I might have missed something. If anyone has any ideas please chime in! TIA!
3. Fuel Pump
The fuel pump of the g28 gets a signal from the RPM sensor. The GM-style transmitter is the same as the G4 and both function in the 80, 100, 200, UrS and RS2 cars so you can easily find one at a junkyard or from a parts store. My Web Site is easy to test them: simply switch your DMM into resistance mode and measure the distance between pins 1 and 2 (with the bump at the connector end facing upwards). They should be infinite Ohms.
4. ECU
Our 20vt turbo (3B, AAN, ABY and ADU) engines have an ECU that must know the speed and position of the crankshaft in order to make decisions regarding timing of the fuel injector, for example. It uses a Crank Position Sensor G4 and an Engine Speed Sensor G28 to achieve this. If either of these goes bad you will get codes on the diagnostic scanner which can lead to engine shutdown.
Some of the symptoms of a failed G28 sensor include an inaccurate gearbox rev counter and gears that shift faster than normal and/or misfiring when you are in gear. If you have any of these issues, it is most likely that your sensor is deteriorating and should be replaced. They're inexpensive and easy to locate particularly in the case of a Bosch unit like ours. You can also choose the GM version of this unit is also a good choice.
5. Tachometer
A failing engine speed sensor could be the reason behind a slew of problems in your vehicle. It is an important part of the transmission in your Audi, as it transmits information to the ECU about how fast or slow the engine is spinning. When this sensor fails, it will affect the performance of the transmission, as well as the other car's components.
The G5 engine speed sensor is situated on the outside of the transmission just above the flywheel ring gear and sends a signal directly to the ECU at pin T55/49 via an uncolored wire. The ECU uses this signal to regulate fuel and boost, as well as timig. It also transmits it to the G5 Tachometer inside the instrument cluster. You can check for sensor failure by checking continuity from the sensor to the tachometer. Additionally, you can 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 as well as pin T26a/12. You should detect a resistance of approximately 1000 ohms in these areas. 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 the best ones could be available in wrecking yards.