How to Replace an Audi A3 key Fob replacement G28 Engine Speed Sensor

Charles the Humble Technician shows how to replace the G28 Engine Speed Sensor. The sensor is located near the edges of the transmission, above the flywheel ring gear. It transmits a signal the ECU via a grey wire (T55/49) and then to the tachometer in the instrument cluster.

1. Engine Speed Sensor

The grey wire is situated on the edge of transmission, just above the flywheel ring. This sensor sends signals through the grey wire to pin T55/49. The ECU then utilizes this information to regulate the boost, fuel, and timig. It also sends a signal 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 must know when the crankshaft reached TDC, and the position of the camshaft, in order to activate the spark and injectors.

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

Testing is a bit challenging since there are two pins for the connector and they perform different functions but the best way to test it is to measure resistance between the sensor and the ECU. It should read about 1000 ohms if the sensor is at full operation. If you are having problems with this sensor, look for signs of coolant or oil in the connector bay.

2. Injectors

Yesterday, when accelerating from highway paytoll at full speed I noticed a significant drop in power. It was as if the engine was running out of gas. Or, my injectors weren't firing. Today, audi spare key i pulled out the spark plugs. Three were soaked with gazoline and the fourth was dry. I placed a tissue over each injector hole and when I start the engine with no sparks, the three that have gazoline pop right out. The 4th one remains closed. I tried to test the ground connections of ECU pins 14,30 and 48/55. I found 0ohm. I assume that the problem is in another location.

I also tried to reset the PID with no success. The audi car keys will start when the G28 is unplugged, and it is running fine with the G28 plugged in. However, the intermittent misfire problem persists at higher RPM. The coolant sensor (G62), even when it is unplugged, shows an ice temperature of -49c. I also noticed that the oil gauge in the cockpit shows 2 bar when the actual pressure is zero.

I'm not certain what to do, i believe that i've eliminated everything else. I'm worried that i might have missed something. Please let me know should you have any suggestions! TIA!

3. Fuel Pump

The fuel pump in the g28 receives a signal from the RPM sensor. The GM-style transmitter is identical to the G4 and both function in the 80 100 200, UrS and Audi Replacement Car Keys RS2 cars so you can easily find one at a salvage yard or from a parts store. It is simple to test them to do - just put your DMM in resistance mode and measure the resistance between pins 1 (with the bump on the connector's end up) and 2 (2nd from the left on the black connector's side). They must be infinite Ohms.

4. ECU

The ECU of our 20vt turbo (3B AAN ABY ADU) engines needs to know the speed and position of the crankshaft in order to make a decision about timing of fuel injectors, etc. It makes use of a Crank Position Sensor G4 and an Engine Speed Sensor G28 to achieve this. If you encounter a problem with either of these, the diagnostic scanner will display codes that could cause an engine shut down.

Some of the signs of a failing G28 sensor are an inaccurate rev counter for the gearbox, gears shifting quicker than normal and/or a misfire when you are in gear. It is likely that your sensor is failing and requires to be replaced if you notice any of these symptoms. They are cheap and easy-to-find especially if they're an Bosch model like ours. Alternatively, GM's version of this component is an option.

5. Tachometer

A failing engine sensor could cause a variety of issues within your vehicle. It is an important part of the transmission in your audi tt key since it sends information to the ECU on how fast or slow the engine is spinning. If this sensor fails, it will disrupt the performance of the transmission as well as the other car's components.

The G5 engine sensor is located near the edge of the transmission, just above the flywheel ring. It transmits a signal via gray wire to ECU pin T55/49. The ECU then uses and processes the signal to control fuel, timig, and boost as well as transmitting it to the G5 tachometer in the instrument cluster. You can test the sensor for failure by checking continuity between it and the tachometer, between the ECU pin T55/49 and the instrument cluster connection on pin T6a/1 (trace [79]) as well as between T6a/1, and the instrument cluster pin T26a/12. There should be the resistance to be around 1000 ohms in these areas. This part is common across the audi tt key case 80-100-200-RS2 model, ranging from the 1985 MC all the way up to the 1997 UrS AN and the 1995 RS2 Du, so you might find them in wrecking yards.