How to Replace an Audi G28 Engine Speed Sensor
Charles the Humble Technician shows how to replace the G28 Engine Speed Sensor. The sensor is located on the outside of the transmission just above the flywheel gear. It sends a signal to the ECU via a grey wire (T55/49), 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 the grey wire. The ECU uses this information to regulate the amount of fuel and boost. It also sends an alert 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 also the position of the camshaft, in order to activate the spark and injectors.
If this sensor fails when it fails, the ECU will display a P00160 error code. This indicates that the Crank Shaft is out of line with the Intake Camshaft. It could also be a sign of the possibility of a chain stretch or jumped chain link in the upper chain of timing. However the code will not appear on its own without additional information from other sensors (G4 and G40).
Testing is a bit challenging since there are two connector pins and they have different functions but the best method of testing it is by measuring resistance between the sensor and the ECU. If the sensor is operational, it should read around 1000 ohms. If you are having problems with this part, check for signs of oil or coolant in the connector bay.
2. Injectors
Yesterday, while accelerating from the highway paytoll at full speed I noticed a significant reduction in power. It was as if the engine was running out of gas. Or, audi a4 spare key were not firing. In the morning, i removed the spark plugs. Three were drenched in gazoline, the fourth one was dry. When i crank the engine without sparks, I put a piece of tissue on the top of each of the injector holes and the 3 that were drenched in gazoline pop out, but the 4th stay shut. I checked the ground connection on ECU pins 14/55, 30/55 and 48/55. I got 0ohm. So i assume the problem is somewhere else.
I also tried to reset the PID but without success. The car is able to start if the G28 is unplugged and is running fine when it is plugged in however it has intermittent misfire issues at higher RPM. The temperature sensor for the coolant (G62) shows the wrong temperature of -49c even when i unplug it. Also, i noticed that the gauge for oil pressure in the cockpit is showing 2 bar while the actual pressure is 0.0 if i crank up the engine.
I don't know what to do. I think I've all other possibilities out. I'm concerned that i may have missed something. Let me know should you have any suggestions! TIA!
3. Fuel Pump
The fuel pump of the g28 receives a signal from the RPM sensor. The GM-style sensor 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 in a local parts store. It is simple 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's end facing upwards). They should 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 regarding fuel injector timing etc. It makes use of a Crank Position Sensor G4 and an Engine Speed Sensor G28 to achieve this. If you have a problem with either of these sensors, the diagnostic scanner will display codes that could cause an engine shut down.
A failing G28 sensor could result in an inaccurate speed counter for the gearbox or a gearbox that shifts faster than normal, or a misfire while in gear. It is possible that the sensor is failing and needs to be replaced if you experience any of these symptoms. The good news is they are quite affordable and readily available particularly when you're looking at a Bosch model, which is what we have. Alternatively, audi a3 key replacement of this part is also a good choice.
5. Tachometer
A damaged engine sensor could cause a myriad of issues in your car. It is a crucial part of your Audi's transmission, because it communicates to the ECU about how fast or slow the vehicle'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 speed sensor is situated on the outside of the transmission just above the flywheel ring gear. It sends a signal to the ECU at pin T55/49 through an uncolored wire. The ECU uses this signal to regulate the flow of fuel and boost and also timig. It also transmits it 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. Additionally, you can examine the continuity between pins 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 approximately 1000 ohms resistance between those two pins. This is a common part that is found 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.