How to Replace an audi key G28 Engine Speed Sensor

In this video, Charles the humble mechanic demonstrates how to replace the G28 engine speed sensor. This sensor is located near the transmission's edge over the flywheel gear. It sends a message to the ECU via an uncolored wire T55/49, then to the tachometer on the instrument cluster.

1. Engine Speed Sensor

The grey wire is located on the edge of transmission, directly above the flywheel ring. The 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 an alert to the G5 Tachometer within the instrument cluster.

The sensor serves as a reference for comparing with the G40 Camshaft Position Sensor. The ecu must know when the crankshaft has reached TDC, and the location of the camshaft to trigger the spark and injectors.

If this sensor audi lost key fails, the ECU will display the P00160 error, which means the Crank Shaft and Intake Camshaft are out of sync and could indicate chain stretch or a jumped link on the upper chain of timing. The code won't show without the additional information supplied by other sensors (G4 or G40).

It is a little tricky to test as there are different pins on the connector and they all have different functions. The best way to do it is to measure the resistance between the ECU and the sensor. If the sensor is operational, it should read approximately 1000 ohms. If you are having problems with this component, look for signs of oil or coolant in the connector bay.

2. Injectors

Yesterday accelerating full speed from highway paytoll, i experienced massive power loss as if the engine was running out of gas or injectors aren't firing at all. In the morning, i removed the spark plugs, 3 were drenched in gazoline, the 4th one was dry. When I start the engine, there are no sparks, i place a tissue on top of each injector hole, the 3 drenched with gazoline pop out, but the 4th one stays shut. I tested the ground connection of ECU pins 14,30, and 48/55. I found 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 unplugged, and it runs fine with the G28 plugged in. However, the intermittent misfire problem continues to occur at higher RPM. The coolant temperature sensor (G62) shows the wrong temp value -49c, even if I unplug it. Also, i 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 don't know what to do. I think I've eliminated everything else. But i'm worried that i might have missed something. If anyone has any ideas please let me know! TIA!

3. Fuel Pump

The fuel pump of the g28 receives a signal from the RPM sensor. The GM-style transmitter 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 salvage yard or at a parts store. It is simple to test them by putting your DMM in resistance mode and measure between pins 1 (with the bump on the connector end up) and 2 (2nd from left on the black connector's side). They should be infinite Ohms.

4. ECU

The ECU in our 20vt turbo (3B AAN ABY ADU) engines needs to be aware of the position and speed the crankshaft to make decisions regarding fuel injector timing, etc. To accomplish this, it uses a Crank Position Sensor (G4) and an Engine Speed Sensor (G28). If either of these goes bad you will get codes on the diagnostic scanner which can lead to engine shutdown.

Some of the symptoms of a failing G28 sensor include an inaccurate rev counter in the gearbox and gears that shift faster than normal and/or a misfire when you are in gear. It is likely that your sensor is failing and needs to be replaced if you experience any of these signs. They're inexpensive and easy to locate particularly when they're an Bosch model like ours. Alternatively, the GM version of this unit is also a good choice.

5. Tachometer

A damaged engine sensor could cause a number of problems within your vehicle. It's a vital component of your Audi Replacement Key Fob's transmission, as it sends information to the ECU about how fast or slow the car's crankshaft is turning. If this sensor fails, it will affect the performance of the transmission, as well as the other car's components.

The G5 engine speed sensor is located at the edge of the transmission just above the flywheel ring gear. It sends a signal directly to the ECU at pin T55/49, via a grey wire. The ECU then processes the signal to control the flow of fuel, timig and boost and then transmitting it to the G5 tachometer in the instrument cluster. You can test for sensor failure by examining the continuity of the sensor to the tachometer. You can also examine the continuity between pins T55/49 of the ECU and pin T6a/1 of the instrument cluster (trace [79trace [79]) and between pin T6a/1 as well as pin T26a/12. You should observe approximately 1000 ohms of resistance between those two pins. This is a standard part across the audi keyfob 80, 100, 200, UrS and RS2 range from 1985 MC through the 1997 UrS AAN and 1995 RS2 ADU. Good parts could be found in wrecking yards.