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How to Replace an audi a3 key fob replacement new key (click for info) G28 Engine Speed Sensor

In this video, Charles the Humble Mechanic demonstrates how to replace the G28 engine speed sensor. The sensor is located near the transmission's edge over the flywheel gear. It transmits a signal the ECU via an uncolored wire (T55/49) which is then sent to the tachometer in the instrument cluster.

1. Engine Speed Sensor

Located on the edge of the transmission above the flywheel ring gear, the G28 Engine Speed Sensor sends an electrical signal to ECU pin T55/49 via a grey wire. The ECU uses this information to control boost and fuel. It also sends an indication to the G5 tachometer inside the instrument cluster.

The sensor is used to link with the G40 Camshaft position Sensor. The ecu must know when the crankshaft is TDC and where the camshaft is located so that it can activate spark and injectors according to the situation.

If this sensor fails the ECU will show an error code P00160 which indicates that the Crank Shaft and Intake Camshaft are out of sync and could indicate the chain is stretched or a jump link on the upper chain of timing. The code will not appear without the additional information supplied by other sensors (G4 or G40).

Testing is a bit tricky because there are two pins for the connector and they serve different purposes but the best method 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 are having problems with this part, check for signs of coolant or oil in the connector bay.

2. Injectors

Yesterday, as i was accelerating off the highway paytoll at a high speed I noticed a massive drop in power. It was like the engine was running out of gas. Or, my injectors weren't firing. Today, i pulled out the spark plugs, 3 were drenched in gazoline, the fourth one was dry. I placed a tissue over each injector hole, and when I start the engine with no sparks, the three with gazoline jump out. The fourth one remains shut. I inspected the ground connection on ECU pins 14/55, 30/55 and 48/55. i get zero Ohm. I'm assuming that the issue is in another location.

I also tried to reset the PID but without success. The car will start when the G28 is disconnected, but it is running fine with the G28 connected. However the intermittent misfire issue persists at higher RPM. The coolant temperature sensor (G62) shows the wrong temp value -49c even when i unplug it. I also noticed that the oil gauge in the cockpit shows 2 bar while the actual pressure is zero.

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

3. Fuel Pump

The fuel pump of the g28 gets a signal from the RPM sensor. The GM-style sensor is identical to the G4 and they both work in the 80 100 200, UrS and RS2 cars so you can easily find one at a salvage yard or at a parts store. Testing them is easy - 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 of our 20vt turbo (3B AAN ABY) engines needs to know the speed and position of the crankshaft to determine fuel injector timing, etc. To accomplish this, it uses a Crank Position Sensor (G4) and an Engine Speed Sensor (G28). If you have a problem with either one of these, the diagnostic scanner will show codes that could cause an engine shut down.

A malfunctioning G28 sensor can cause an inaccurate speed counter for the gearbox or a gearbox that shifts faster than normal, or a misfire in gear. If you have any of these issues, it is likely your sensor is going bad and should be replaced. The good thing is that they are very affordable and readily available, especially when you're looking at an Bosch unit which is what ours are. If you prefer, GM's version of this component is an option.

5. Tachometer

A failing engine speed sensor could be the reason behind numerous problems in your vehicle. It's an essential component of the transmission of your audi advance key because it relays information to the ECU on how fast or slowly the engine of the car is spinning. This sensor can cause the transmission to fail and other components of the car to be affected.

The G5 engine sensor is located at the edge of the transmission, just above the flywheel ring. It transmits a signal via a gray wire to the ECU pin T55/49. The ECU then processes this signal to control the flow of fuel, timig and boost, and also sends it on to the G5 Tachometer located in the instrument cluster. You can determine if the sensor is in 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 [79]), and between pin T6a/1 and pin T26a/12. There should be a resistance of approximately 1000 ohms between these two points. This is the same across the audi car keys 80-100-200-RS2 model, ranging from the 1985 MC up to the 1997 UrS AN and the 1995 RS2 Du, so you might find good ones in wrecking yards.