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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. The sensor is situated near the edges of the transmission, above the flywheel ring gear. It transmits a signal to the ECU via the grey wire (T55/49) and then to the tachometer located in the instrument cluster.

1. Engine Speed Sensor

The grey wire is located on the outside of the transmission, just above the flywheel ring. The sensor sends a signal via 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 in the instrument cluster.

The sensor is used as a reference to correlate with the G40 Camshaft Position Sensor. The ecu needs to know when the crankshaft reached TDC and also the position of the camshaft, to trigger the spark and injectors.

If this sensor fails, the ECU will display a P00160 code which means the Crank Shaft and Intake Camshaft are not in sync and could indicate chain stretch or a jumped link on the upper timing chain. audi car keys won't appear without the additional information supplied by other sensors (G4 or G40).

Testing is a bit tricky because there are two connector pins, and they serve different purposes but the best method of testing it is to measure the resistance between the sensor and the ECU. When the sensor is operational, it should read around 1000 ohms. Look for evidence of coolant or oil in the connector bay if you have issues with this component.





2. Injectors

Yesterday, while accelerating from the highway paytoll at a high speed I noticed a massive decrease in power. It was as if the engine had run out of gas. Or, my injectors weren't firing. I pulled out the spark plugs this morning, 3 were soaked in gasoline, and the 4th was dry. I placed a tissue over each injector hole and when I start the engine without sparks, the ones with gazoline jump out. The 4th one remains shut. I checked the ground connection of ECU pins 14,30 and 48/55. I found zero ohm. I think the issue is elsewhere.

I also tried to reset PID but without success. The car will start when the G28 is unplugged, and it is running fine with the G28 connected. However, the intermittent misfire problem persists at higher RPM. The coolant temperature sensor (G62) shows the wrong temp value -49c even when i unplug it. I also noticed that the oil gauge in the cockpit shows 2 bar but the actual pressure is 0.

I'm not sure what to do, i think i've pretty much ruled out everything else. However, i'm afraid that I might have missed something. If anyone has suggestions, please let me know! TIA!

3. Fuel Pump

The fuel pump in the g28 is activated by a signal by the RPM sensor. The GM-style transmitter 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 salvage yard or at a parts store. It is simple to test them - put 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 the left on the black connector's end). They should be infinite Ohms.

4. ECU

Our 20vt turbo (3B AAN, ABY and ADU) engines have an ECU that needs to know the position and speed of the crankshaft in order to make decisions about timing of the fuel injectors, etc. It utilizes a Crank Position Sensor G4 and an Engine Speed Sensor G28 to accomplish this. If either of these sensors go badly, you will see codes on the diagnostic scanner that can cause the engine to shut down.

A malfunctioning G28 sensor could cause an inaccurate speed counter for the gearbox, a gearbox that shifts faster than normal, or a misfire while in gear. If you have any of these issues it is likely your sensor is going bad and needs replacing. The good news is that they are very cheap and easy to find particularly if you're looking at the Bosch sensor, which is what ours are. Alternately, GM's version this part would be an excellent choice.

5. Tachometer

A damaged engine sensor could cause a myriad of issues within your vehicle. 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 turning. This sensor could cause the transmission to malfunction and other car components to be affected.

The G5 engine sensor is located at the outskirts of the transmission, just above the flywheel ring. It sends an electrical signal through an uncolored wire to the ECU pin T55/49. The ECU then processes this signal to regulate the flow of fuel, timig and boost, and also transmitting it to the G5 tachometer in the instrument cluster. You can check for sensor failure by examining the continuity of the sensor to the tachometer. You can also verify continuity between pin T55/49 of the ECU and pin T6a/1 of the instrument cluster (trace [79trace [79]) and between pin T6a/1 as well as pin T26a/12. You should observe approximately 1000 ohms of resistance between those two pins. This is a typical part across the Audi 80, 100, 200, UrS and RS2 range from 1985 MC until the 1997 UrS AAN and 1995 RS2 ADU so good ones could be available in wrecking yards.