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How to Replace an audi Q3 Key G28 Engine Speed Sensor

Charles the Humble Technician shows how to replace the G28 Engine Speed Sensor. This sensor is located on the outside of the transmission just above the flywheel gear. It transmits a signal to the ECU via the grey wire T55/49 and then to the tachometer on the instrument cluster.

1. Engine Speed Sensor

It is located on the outside of the transmission, above the flywheel ring gear G28 Engine Speed Sensor sends signals to ECU pin T55/49 via a grey wire. The ECU utilizes this information to regulate boost and fuel. It also sends an indication to the G5 tachometer inside the instrument cluster.

The sensor serves 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 located so that it can trigger spark and injectors in the right way.

If this sensor fails, the ECU will throw the P00160 error, which means the Crank Shaft and Intake Camshaft are not in sync and possibly indicating chain stretch or a jumped link on the upper timing chain. The code won't show without the additional information supplied by other sensors (G4 or G40).

Testing is a bit challenging as there are two different connector pins, and they have different functions however the best method to test it is by measuring resistance between the sensor and the ECU. It should read around 1000 ohms when the sensor is in full operation. Look for signs of coolant, or oil in the connector bay if there are issues with this part.

2. Injectors

Yesterday, while accelerating from the highway paytoll at maximum speed, i noticed a huge reduction 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 4th was dry. I placed a tissue over each injector hole and when i start the engine with no sparks, the ones with gazoline jump out. The 4th one stays closed. I checked the ground connection on ECU pins 14/55, 30/55 and 48/55. I get zero Ohm. Therefore, i think the issue is somewhere else.

I also tried to reset the PID but with no luck. The car can start if the G28 is unplugged and replacement key for audi a3 is running fine when it is connected, but still has intermittent misfire issues at higher RPM. The coolant temperature sensor (G62) shows the wrong temperature of that is -49c even after unplugging it. I also noticed that the gauge for oil pressure in the cockpit is showing 2 bar while the actual pressure is 0.0 if i crank up the engine.

I'm not sure what to do, but i believe that i've ruled out everything else. However, i'm afraid that i might have missed something. If anyone has any suggestions, please share them! TIA!

3. Fuel Pump

The fuel pump in the g28 gets a signal from the RPM sensor. The GM-style transmitter functions similarly to the G4 sender, and both operate on the 80,100,200, UrS, and RS2 vehicles. You can easily locate an extra in a wrecking shop or parts store. It is easy to test them - just put your DMM into resistance mode and determine the distance between pins 1 and 2 (with the bump on the connector's edge facing upwards). They must be infinite Ohms.

4. ECU

Our 20vt turbo (3B AAN, ABY and ADU) engines have an ECU that must know the speed and position of the crankshaft in order to make decisions regarding timing of the fuel injector, for example. It utilizes a Crank Position Sensor G4 and an Engine Speed Sensor G28 to accomplish this. If you have a problem with either one of these, the diagnostic scanner will display codes that could lead to an engine shutdown.

The signs of a failed G28 sensor include an inaccurate gearbox rev counter the gears are shifting faster than normal, and/or a misfire when in gear. It is likely that your sensor is failing and requires to be replaced if you encounter any of these signs. The good news is that they are quite affordable and readily available particularly if you're looking at the Bosch sensor, which is what we have. Alternately, the GM version of this part is also a good choice.

5. Tachometer

A failing engine sensor could cause a number of problems in your car. It's a crucial component of the transmission in your new audi key since it sends information to the ECU regarding how fast or slowly the engine is turning. If the sensor fails, it can cause problems for the transmission and the other car's components.

The G5 engine sensor is located at the edge of the transmission, just above the flywheel ring. It transmits a signal via an uncolored wire to the ECU pin T55/49. The ECU is then able to process this 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 check the sensor for failure by examining the continuity between it and the tachometer. You can also check continuity 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 detect a resistance of approximately 1000 ohms in these areas. This is the same across the audi spare key 80-100-200-RS2 series, starting from the 1985 MC all the way up to the 1997 UrS AN and the 1995 RS2 Du, so you might find some good ones in wrecking yards.