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How to Replace an audi connect key G28 Engine Speed Sensor

Charles the Humble Technician teaches you how to replace the G28 Engine Speed Sensor. This sensor is located at the edge of transmission, above the flywheel gear. It transmits a signal to the ECU via an uncolored wire (T55/49) which is then sent to the tachometer located in the instrument cluster.

1. Engine Speed Sensor

The grey wire is situated on the outside of the transmission, just above the flywheel ring. This sensor sends an electrical signal through the grey wire to pin T55/49. The ECU then uses this information to control the flow of fuel, timig and boost. It also sends an indication to the G5 Tachometer located in the instrument cluster.

The sensor serves as a reference for comparing with the G40 Camshaft Position Sensor. The ecu has to know when the crankshaft has reached TDC and also where the camshaft lies so that it can activate the spark and injectors.

If this sensor fails to function, the ECU will display an error code P00160. This means that the Crank Shaft is out of alignment with the Intake Camshaft. It could also be a sign of an issue with the chain or a jumped chain link in the upper chain. However, the error code won't appear on its own, without additional information from other sensors (G4 and G40).

Testing is a bit challenging because there are two connector pins and they perform different functions but the best method to test it is to measure resistance between the sensor and the ECU. When the sensor is operational, it should be reading around 1000 ohms. Check key for audi signs of coolant, or oil in the connector bay if there are issues with this part.

2. Injectors

Yesterday, as i was accelerating off the highway paytoll at maximum speed, i noticed a huge reduction in power. It was as if the engine was running out of gas. Or my injectors weren't firing. This morning i pull out the spark plugs, three were soaked with gazoline and the 4th one was dry. When I crank the engine, there are no sparks, i place a tissue on the top of each hole in the injector and the 3 that were drenched in gazoline jump out but the 4th stays shut. I tested the ground connection of ECU pins 14,30 and 48/55. I got 0ohm. Therefore, i think the issue is somewhere else.

I also tried to reset the PID but with no luck. The car will start when the G28 is disconnected, but it is running fine with the G28 plugged in. However, the intermittent misfire problem continues to occur at higher RPM. The coolant sensor (G62), even if it is not plugged in, shows a temperature of -49c. Also i noticed that the gauge for oil pressure in the cockpit shows 2 bar, whereas the actual pressure is 0.0 if i crank up the engine.

I'm not sure what to do. I feel like i've pretty much eliminated everything else. I'm concerned that i may have missed something. Let me know if you have any ideas! TIA!

3. Fuel Pump

The fuel pump on the g28 is activated by a signal sent 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 which is why you can easily locate one at a junkyard or from a parts store. Test them out to do - just put your DMM in resistance mode and measure the resistance between pins 1 (with the bump on the connector end up) and 2 (2nd from the left on the black end of the connector). They must be infinite ohms.

4. ECU

The ECU in our 20vt turbo (3B AAN ABY ADU) engines must be aware of the position and speed of the crankshaft to determine timing of the fuel injector, etc. It makes use of a Crank Position Sensor G4 and an Engine Speed Sensor G28 to accomplish this. If you encounter a problem with either of these sensors, the diagnostic scanner will display the codes that could trigger the engine shutting down.

A failing G28 sensor could cause an inaccurate gearbox speed counter and a gearbox which shifts faster than normal, or a misfire in gear. It is possible that the sensor is failing and requires to be replaced if you encounter any of these symptoms. They are cheap and easy-to-find particularly if they're a Bosch model like ours. You can also choose the GM version of this part is also a great option.

5. Tachometer

A failing engine sensor could cause a myriad of issues in your car. It's an essential component of the Audi Key shell's transmission since it relays information to the ECU about how fast or slow the vehicle's crankshaft is rotating. If this sensor fails, it will affect the performance of the transmission and the other car's components.

The G5 engine speed sensor is located on the edge of the transmission just above the flywheel ring gear and transmits a signal to the ECU at pin T55/49, via a grey wire. The ECU uses this signal to control the flow of fuel and boost and also timig. It also sends it to the G5 Tachometer located in the instrument cluster. You can check 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 [79trace [79]) as well as between T6a/1, and the instrument cluster pin T26a/12. It should show approximately 1000 ohms of resistance between those points. This is a common part that is found across the audi spare key replacement 80 100, 200, UrS and RS2 range from 1985 MC to the 1997 UrS AAN and 1995 RS2 ADU, so the best parts could be found in wrecking yards.