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 on the outside of the transmission over the flywheel gear. It transmits a signal to the ECU via an uncolored wire T55/49, then to the tachometer on the instrument cluster.
1. Engine Speed Sensor
The grey wire is situated on the outside of the transmission, just above the flywheel ring. The sensor transmits a signal via the grey wire to pin T55/49. The ECU uses this information to regulate fuel and boost. It also sends an indication to the G5 Tachometer in instrument cluster.
The sensor serves as a reference for comparing with the G40 Camshaft Position Sensor. The ecu must know when the crankshaft is TDC and the location of the camshaft so it can start spark and injectors in the right way.
If this sensor fails the ECU will throw a P00160 code which means the Crank Shaft and Intake Camshaft are out of sync, possibly indicating chain stretch or a jumped link on the upper timing chain. However, the error code won't 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 pins on the connector, and each has its own functions. The best way to do it is to measure the resistance between the ECU and the sensor. It should read around 1000 ohms when it is operating at its maximum. Check for signs of coolant, or oil in the connector bay if there are problems with this part.
2. Injectors
Yesterday, when i was accelerating to the fullest speed from highway paytoll, I experienced massive power loss as if the engine was running out of gas or injectors are not firing anymore. I took out the spark plugs this morning and found that 3 were soaked with gasoline and the fourth was dry. I put tissue over each hole in the injector and when I start the engine with no sparks, the 3 that have gazoline pop right out. The 4th one remains closed. I checked the ground connection of ECU pins 14,30, and 48/55. I got 0ohm. audi q5 locked keys in car assume that the problem is elsewhere.
I also tried to reset PID but without success. The car is able to start if the G28 is not plugged in and is running fine when it is connected but it still is experiencing intermittent misfires at higher RPM. The coolant temperature sensor (G62) shows the wrong temp value that is -49c even after unplugging it. I also noticed that the oil gauge in the cockpit shows 2 bar when the actual pressure is 0.
I'm not certain what to do, but i think i've pretty much eliminated everything else. But i'm worried that i might have missed something. Please let me know If you have any suggestions! TIA!
3. Fuel Pump
The fuel pump of the g28 gets a signal from the RPM sensor. The GM-style sender 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. It 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's end facing upwards). They must be infinite Ohms.
4. ECU
The ECU in our 20vt turbo (3B AAN ABY ADU) engines must know both the position and speed of the crankshaft in order to make a decision about timing of fuel injectors, etc. To accomplish this, it utilizes a Crank Position Sensor (G4) and an Engine Speed Sensor (G28). If you encounter a problem with either one of these, the diagnostic scanner will show codes that could cause an engine shutdown.
A damaged G28 sensor could cause an inaccurate speed counter for the gearbox and a gearbox which shifts more quickly than normal, or an unfire when in gear. It is likely that the sensor is failing and needs to be replaced if you experience any of these symptoms. The good thing is that they are very affordable and easily accessible particularly in the case of an Bosch sensor, which is what ours are. If you prefer, GM's version of this part is an excellent choice.
5. Tachometer
A malfunctioning engine speed sensor could be the reason behind a slew of issues with your vehicle. It is a crucial part of your Audi's transmission, because it communicates to the ECU about how fast or slow the car's crankshaft is spinning. When this sensor 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 edge of the transmission, over the flywheel ring. It transmits a signal via an uncolored wire to the ECU pin T55/49. The ECU utilizes this signal to control the amount of fuel and boost, as well as timig. It also sends it to the G5 Tachometer inside the instrument cluster. You can test the sensor for failure by checking continuity between it and the tachometer. You can also check continuity between ECU pin T55/49 and the instrument cluster connection on pin T6a/1 (trace [79]) and between T6a/1 and the instrument cluster pin T26a/12. You should see around 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, so the best ones might be availble in wrecking yards.