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 just above the flywheel gear. It sends a signal to the ECU via the grey wire (T55/49), then to the tachometer located in the instrument cluster.
1. Engine Speed Sensor
Located on the edge of the transmission just above the flywheel ring gear G28 Engine Speed Sensor sends a signal to ECU pin T55/49 via an uncolored wire. The ECU uses this information to regulate the amount of fuel and boost. It also sends an alert to the G5 Tachometer located in the instrument cluster.
The sensor is used as a reference for comparing with the G40 Camshaft Position Sensor. The ecu needs to know when the crankshaft is TDC and where the camshaft is so it can trigger spark and injectors accordingly.
If this sensor fails the ECU will show a P00160 code which means the Crank Shaft and Intake Camshaft are not in sync, possibly indicating chain stretch or a jumped link on the upper chain of timing. The code will not appear without the additional information provided by other sensors (G4 or G40).
Testing is a bit challenging as there are two different connector pins, and they perform different functions however the best method to test it is to measure the resistance between the sensor and the ECU. When the sensor is fully operational, it should read approximately 1000 ohms. If you're having issues with this sensor, look for evidence of oil or coolant in the connector bay.
2. Injectors
Yesterday, when accelerating from highway paytoll at full speed I noticed a massive decrease in power. It was like the engine was running out of gas. Or my injectors were not firing. I took out the spark plugs this morning, three were soaked with gasoline and the fourth was dry. When i crank the engine with no sparks i put tissue on the top of each hole in the injector and the 3 that were drenched in gazoline pop out, but the 4th stays shut. I inspected the ground connection on ECU pins 14/55/30/55/48/55/14/55/48/ i get zero Ohm. So i assume the problem is somewhere else.
I also tried to reset PID but without success. The car is able to start if the G28 is disconnected and is running fine when it is plugged in, but still has the intermittent misfire issue at higher RPM. The coolant temperature sensor (G62) shows the wrong temp value -49c even when i unplug it. Also i noticed that the gauge for oil pressure in the cockpit shows 2 bar, whereas the actual pressure is 0.0 when I crank up the engine.
see here now 'm not sure what to do. I believe that I've eliminated everything else. But i'm worried that i might have missed something. If anyone has suggestions, please chime in! TIA!
3. Fuel Pump
The fuel pump in the g28 receives signals from the RPM sensor. The GM-style transmitter functions similarly to the G4 sender and both work on the 80,100,200, UrS, and RS2 vehicles. You can easily find a spare in a wrecking shop or parts store. It is simple to test them by putting your DMM in resistance mode and measure the resistance between pins 1 (with the bump on the connector's side up) and 2 (2nd from left on the black connector's end). They must 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 of these sensors, the diagnostic scanner will show the codes that could trigger an engine shutdown.
A failing G28 sensor can cause an inaccurate speed counter for the gearbox and a gearbox which shifts faster than normal, and/or a misfire while in gear. It is possible that your sensor is failing and needs to be replaced if you experience any of these symptoms. They are cheap and easy-to-find especially if they're a Bosch sensor like ours. Alternately, the GM version of this unit is also a good choice.
5. Tachometer
A failing engine speed sensor could be the cause of numerous problems in your vehicle. It is a crucial part of the Audi's transmission because it communicates to the ECU about how fast or slow the vehicle's crankshaft is spinning. This sensor could cause the transmission to malfunction and other car components to be affected.
The G5 engine sensor is located at the edge of the transmission, just above the flywheel ring. It sends signals via an uncolored wire to the ECU pin T55/49. The ECU then uses and processes this signal to regulate fuel, timig and boost as well as transmitting it to the G5 Tachometer located in the instrument cluster. You can test the sensor for failure by checking continuity between it and the tachometer, between ECU pin T55/49 and the instrument cluster connection on pin T6a/1 (trace [79trace [79]) as well as between T6a/1, and the instrument cluster pin T26a/12. You should see the resistance to be around 1000 ohms in these areas. This is a common 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 parts could be found in wrecking yards.