How to Replace an Audi G28 Engine Speed Sensor
In this video, Charles the Humble Mechanic shows how to replace the G28 engine speed sensor. This sensor is located at the edge of transmission just above the flywheel gear. It transmits a signal the ECU via a grey wire (T55/49), then to the tachometer within the instrument cluster.
1. Engine Speed Sensor
The grey wire is situated on the outside of the transmission, directly above the flywheel ring. The sensor sends an electrical signal through the grey wire to pin T55/49. The ECU then utilizes this information to regulate the boost, fuel, and timig. It also sends an indication to the G5 Tachometer located in the instrument cluster.
The sensor is used to connect the G40 Camshaft position Sensor. The ecu must know 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 when it fails, the ECU will display a P00160 error message. This means that the Crank Shaft is not in alignment with the Intake Camshaft. lost audi key could also be a sign of a chain stretch or a jumped chain link in the upper chain of timing. However the code will not be displayed on its own without additional information from other sensors (G4 and G40).
It can be a bit difficult to test because there are different pins on the connector and each one has 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 at full operation. If you're having issues with this sensor, look 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 huge decrease in power. It was as if the engine had run out of gas. Or my injectors weren't firing. This morning i pull out the spark plugs, three were drenched with gazoline the 4th one was dry. I put tissue over each injector hole and when i start the engine without sparks, the three that have gazoline pop right out. The fourth one remains shut. I checked the ground connection of ECU pins 14,30 and 48/55. I got zero ohm. So i assume the problem is in another place.
I also tried to reset the PID without success. The car will start if the G28 is unplugged and it runs perfectly when it is plugged in, but still has the intermittent misfire issue at higher RPM. The temperature sensor for coolant (G62) shows the wrong temperature value of -49c, even if I unplug it. I also noticed that the oil pressure gauge in the cockpit is showing 2 bar while the actual pressure is 0.0 when I crank up the engine.
I'm not certain what to do, i feel i have pretty much completely ruled out all other possibilities. I'm concerned that i may have missed something. If anyone has any ideas please let me know! TIA!
3. Fuel Pump
The fuel pump in the g28 is activated by a signal from the RPM sensor. The GM-style transmitter is the same as the G4 and they both work in the 80, 100, 200, UrS and RS2 cars which is why you can easily locate one at a junkyard or in a local parts store. It is simple to test them - simply put your DMM into resistance mode and test the distance between pins 1 and 2 (with the bump on the connector's edge facing up). They should be infinite Ohms.
4. ECU
Our 20vt turbo (3B AAN, ABY, and ADU) engines have an ECU that must be aware of the speed and position of the crankshaft in order to make decisions about fuel injector timing etc. In order to do 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 lead to an engine shutdown.
The signs of a failed G28 sensor are an inaccurate rev counter in the gearbox the gears are shifting faster than normal and/or misfiring when you're in gear. If you are experiencing any of these issues it is likely your sensor is failing and needs replacing. The good news is that they are very cheap and readily available, especially in the case of a Bosch unit which is what ours are. Alternately, the GM version of this part is also a great option.
5. Tachometer
A failing engine sensor could cause a variety of issues in your vehicle. It's an essential component of the Audi's transmission since it relays information to the ECU about how fast or slow the vehicle's crankshaft is rotating. This sensor can cause the transmission to fail and other car components to be affected.
The G5 engine speed sensor is located at the edge of the transmission, above the flywheel ring gear and transmits a signal to the ECU at pin T55/49 through an uncolored wire. The ECU then uses and processes this signal to control fuel, timig and boost as well as sends it on to the G5 Tachometer located in the instrument cluster. You can test the sensor for failure by examining the continuity between it and the tachometer, between ECU pin T55/49 and the instrument cluster connection via pin T6a/1 (trace [79]) and between pin T6a/1 and the instrument cluster pin T26a/12. There should be an average resistance of 1000 ohms in these areas. This part is common across the Audi 80-100-200-RS2 model, ranging from the 1985 MC all the way up to the 1997 UrS An and 1995 RS2 DU You may also find some good ones in wrecking yards.