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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 at the top of the transmission above the flywheel ring gear. It transmits a signal 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 just above the flywheel ring gear the G28 Engine Speed Sensor sends a signal to ECU pin T55/49 via an uncolored wire. The ECU utilizes this information to control the amount of fuel and boost. replacement audi key sends a signal to the G5 Tachometer located in the instrument cluster.

The sensor is used as a reference point to connect with the G40 Camshaft Position Sensor. The ecu must know when the crankshaft is TDC and the location of the camshaft so it can activate spark and injectors in the right way.

If this sensor fails, the ECU will display a P00160 error message. This indicates that the Crank Shaft is out of alignment with the Intake Camshaft. It could also indicate a chain stretch or a jumpy chain link in the upper chain. The code won't appear without the additional information provided by other sensors (G4 or G40).

Testing is a bit challenging since there are two connector pins, and they have different functions however the best way to test it is to measure resistance between the sensor and the ECU. When the sensor is fully operational, it should be reading approximately 1000 ohms. If you are having problems with this sensor, look for signs of oil or coolant in the connector bay.

2. Injectors

Yesterday, when i was accelerating to the fullest speed from highway paytoll i had an abrupt drop in power as if the engine was running out of gas or the injectors aren't firing anymore. I pulled out the spark plugs this morning, 3 were drenched in gasoline and the 4th was dry. When I start the engine, there are no sparks, I put a piece of tissue on the top of each hole in the injector and the 3 drenched with gazoline pop out, but the 4th stay shut. I inspected the ground connection on ECU pins 14/55,30/55 and 48/55 i get zero ohm. So i assume the problem is elsewhere.

I also tried to reset the PID with no success. The car will start when the G28 is disconnected, but it works fine when the G28 connected. However the intermittent misfire issue still occurs at higher RPM. The temperature sensor for the coolant (G62) shows the wrong temp value -49c even when i unplug it. I also noticed that the oil pressure gauge in the cockpit shows 2 bar when the actual pressure is 0.0 when I crank up the engine.

I'm not certain what to do, as i feel i have pretty much ruled out everything else. But i am afraid I may have missed something. Please let me know If you have any suggestions! TIA!

3. Fuel Pump

The fuel pump in the g28 is activated by a signal sent by the RPM sensor. The GM-style sender is identical to the G4 and they both work in the 80 100, 200, UrS and RS2 cars so you can easily find one at a junkyard or at 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 end facing upwards). They should be infinite Ohms.

4. ECU





The ECU of our 20vt turbo (3B AAN ABY ADU) engines requires to know both the position and speed the crankshaft in order to make a decision about timing of the fuel injector, etc. In order to do this it uses a Crank Position Sensor (G4) and an Engine Speed Sensor (G28). If you are experiencing issues with either of these sensors, the diagnostic scanner will display codes that could cause an engine shutdown.

The signs of a failing G28 sensor include an inaccurate rev counter in the gearbox the gears are shifting faster than normal and/or a misfire when you are in gear. It is probable that your sensor is failing and requires to be replaced if you notice any of these signs. They are cheap and easy-to-find particularly if they're a Bosch sensor like ours. Alternately, the GM version of this component is also a great option.

5. Tachometer

A failing engine sensor could cause a variety of issues within your vehicle. It's a vital component of your Audi's transmission, since it relays information to the ECU about how fast or slow the car's crankshaft is rotating. This sensor can cause the transmission to fail and other components in the car to be affected.

The G5 engine sensor is located near the edge of the transmission, just above the flywheel ring. It sends a signal via gray wire to ECU pin T55/49. The ECU uses this signal to regulate the flow of fuel and boost as well as timig. It also transmits it to the G5 Tachometer in instrument cluster. You can determine if the sensor is in failure by checking continuity from the sensor to the tachometer. Also, 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 these two points. This is a standard part 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.