How to Replace an audi car key case G28 Engine Speed Sensor

Charles the Humble Technician teaches you how to replace the G28 Engine Speed Sensor. This sensor is situated at the edge of transmission over the flywheel gear. It sends a message to the ECU through an uncolored wire T55/49, then to the tachometer in the instrument cluster.

1. Engine Speed Sensor

The grey wire is situated on the edge of transmission, above the flywheel ring. The sensor transmits 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 a signal to the G5 Tachometer located in the instrument cluster.

The sensor is used to link the G40 Camshaft position Sensor. The ecu has to know when the crankshaft has reached TDC, and where the camshaft lies to trigger the spark and injectors.

If this sensor audi key fobs fails, the ECU will display an error code P00160 which indicates that the Crank Shaft and Intake Camshaft are not in sync, possibly indicating the chain stretching or a jump link on the upper chain of timing. However, the error code won't appear on its own, without additional information from other sensors (G4 and G40).

Testing is a bit tricky as there are two different connector pins and they perform different functions but the most effective way to test it is to measure resistance between the sensor and the ECU. It should read around 1000 ohms when it is operating at its maximum. If you're experiencing issues with this sensor, look for signs of coolant or oil in the connector bay.

2. Injectors

Yesterday accelerating full speed from highway paytoll, i experienced a big cut in power as if the engine was running out of gas or the injectors are not firing at all. Today, i pulled out the spark plugs, 3 were drenched in gazoline, the fourth was dry. When I start the engine without sparks i put tissue on the top of each hole in the injector and the 3 drenched with gazoline pop out, but the 4th stays closed. I tried to test the ground connections of ECU pins 14,30, and 48/55. I got zero ohm. Therefore, i think the issue is somewhere else.

I also tried to reset the PID but with no luck. The car is able to start when the G28 is disconnected and runs fine when it is plugged in however it has intermittent misfire issues at higher RPM. The coolant sensor (G62) even when unplugged, still shows an ice temperature of -49c. Also i noticed that the gauge for oil pressure in the cockpit is showing 2 bar when the actual pressure is 0.0 when i rev the engine.

I don't know what to do. I feel like i've pretty much ruled everything else out. But i'm worried that I might have missed something. If anyone has suggestions, please share them! TIA!

3. Fuel Pump

The fuel pump of the g28 gets 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 Audi Key Fobs RS2 cars so you can easily find one at a junkyard or in a local parts store. It is simple to test them - simply switch 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 must be infinite ohms.

4. ECU

Our 20vt turbo (3B AAN, ABY, and ADU) engines are equipped with an ECU that has to know the position and speed of the crankshaft in order to make decisions about timing of the fuel injectors, etc. To do this, it utilizes 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 shut down.

A malfunctioning G28 sensor could cause an inaccurate speed counter for your gearbox or a gearbox that shifts faster than normal, and/or a misfire in gear. If you have any of these issues it is likely that your sensor is failing and requires replacement. They are cheap and easy-to-find, especially in the case of an Bosch unit like ours. Alternatively, the GM version of this unit is also a good option.

5. Tachometer

A damaged engine sensor could cause a number of problems within your vehicle. It's a vital component of your audi Key Fobs's transmission, since it relays information to the ECU about how the car's crankshaft is turning. This sensor can cause the transmission to malfunction and other car components to be affected.

The G5 engine sensor is located near the edge of transmission, above the flywheel ring. It transmits a signal via a gray wire to the ECU pin T55/49. The ECU then processes the signal to control the flow of fuel, timig and boost, and also sends it on to the G5 tachometer inside the instrument cluster. You can determine if the sensor is in failure by examining the continuity from the sensor to the tachometer. Additionally, you can verify continuity between pin T55/49 of the ECU and pin T6a/1 of the instrument cluster (trace [79]) and between pin T6a/1 and pin T26a/12. You should see around 1000 ohms of resistance between these two points. This is a standard part across the Audi 80, 100 200, UrS and RS2 range from 1985 MC until the 1997 UrS AAN and 1995 RS2 ADU. Good parts could be found in wrecking yards.