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 near the transmission's edge, above the flywheel gear. It transmits a signal the ECU via an uncolored wire (T55/49) which is then sent 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 then uses this information to control fuel, timig and boost. It also sends an indication to the G5 Tachometer located in the instrument cluster.
The sensor is used to connect with the G40 Camshaft position Sensor. The ecu must know when the crankshaft has reached TDC and also the location of the camshaft so that it can activate the spark and injectors.
If this sensor fails to function, the ECU will display an error code P00160. This indicates that the Crank Shaft is out of sync with the Intake Camshaft. It could also be a sign of an issue with the chain or a jump in the chain link of the upper chain of timing. 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 since there are various pins on the connector, and they all have different functions. The best way to do it is by measuring the resistance between the ECU and the sensor. It should read about 1000 ohms if the sensor is in full operation. Look for signs of coolant or oil in the connector bay if you have problems with this part.
2. Injectors
Yesterday, while accelerating at full speed from the highway paytoll, I experienced a big cut in power like the engine is running out of gas or the injectors are not firing any more. Today, i pulled out the spark plugs, 3 were drenched in gazoline, the 4th one was dry. I put tissue over each injector hole and when i turn the engine on without sparks, the 3 with gazoline jump out. The 4th one stays shut. I tested the ground connection on ECU pins 14/55, 30/55 and 48/55. i get zero ohm. Therefore, i think the issue is in another place.
I also tried to reset the PID but with no luck. The car will start if the G28 is unplugged and it runs perfectly when it is connected, but still is experiencing intermittent misfires at higher RPM. spare audi key (G62) shows the wrong temp value -49c even when i unplug it. I also noticed that the oil pressure gauge in the cockpit is showing 2 bar, whereas the actual pressure is 0.0 if i crank up the engine.
I'm not sure what to do. I believe that I've ruled everything else out. However, i'm afraid that I might have missed something. Let me know if you have any ideas! TIA!
3. Fuel Pump
The fuel pump in the g28 gets a signal from the RPM sensor. The GM-style transmitter is identical to the G4 sender and works on the 80,100,200, UrS, and RS2 vehicles. You can easily find a spare in a wrecking shop or parts store. Test them out - put your DMM in resistance mode and take measurements between pins 1 (with the bump on the connector's side up) and 2 (2nd from left on the black end of the connector). 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 in order to make decisions about timing of the fuel injector, for example. It makes use of 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 lead to an engine shut down.
The signs of a malfunctioning G28 sensor are an inaccurate rev counter for the gearbox, gears shifting quicker than normal and/or a misfire when in gear. If you are experiencing any of these issues it is most likely that your sensor is deteriorating and needs replacing. The good news is that they are very cheap and easily accessible particularly when you're looking at a Bosch model, like ours. Alternatively, GM's version of this part is an option.
5. Tachometer
A failing engine sensor could cause a variety of issues within 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 turning. This sensor can cause the transmission to malfunction and other components of the car to be affected.
The G5 engine sensor is located near the edge of transmission, above the flywheel ring. It transmits an electrical signal through gray wire to ECU pin T55/49. The ECU then uses and processes the signal to control fuel, timig, and boost as well as transmitting it to the G5 Tachometer located in the instrument cluster. You can check the sensor for failure by checking continuity between it and the tachometer, between the ECU pin T55/49 and the instrument cluster connection via pin T6a/1 (trace [79]) and between T6a/1 and the instrument cluster pin T26a/12. You should observe around 1000 ohms of resistance between those points. This is a common part 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.