How to Replace an audi Key blade 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 just above the flywheel gear. It transmits a signal to the ECU via the grey wire T55/49 and then to the tachometer located on the instrument cluster.

1. Engine Speed Sensor

It is located on the outside of the transmission just above the flywheel ring gear, the G28 Engine Speed Sensor sends an electrical signal to ECU pin T55/49 through an uncolored wire. The ECU utilizes this information to control boost and fuel. It also sends an alert to the G5 Tachometer located in the instrument cluster.

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

If this sensor fails the ECU will show a P00160 code which means the Crank Shaft and Intake Camshaft are not in sync, possibly indicating the chain is stretched or a jump link on the upper timing chain. The code will not appear without the additional information provided by other sensors (G4 or G40).

It's a bit tricky to test because there are different pins on the connector, and they all have different functions. The best way to do it is by measuring the resistance between the ECU and the sensor. It should read approximately 1000 ohms if the sensor is at full operation. If you're experiencing issues with this component, look for signs of coolant or oil in the connector bay.

2. Injectors

Yesterday, while accelerating at full speed from the highway paytoll, I experienced an abrupt drop in power as if the engine was running out of gas or the injectors are not firing anymore. This morning i pull out the spark plugs. Three were drenched in gazoline, the fourth was dry. I put a piece of tissue over each injector hole and when I turn the engine on without sparks, the three with gazoline jump out. The fourth one remains shut. I tested the ground connection of ECU pins 14,30, and 48/55. I got 0ohm. I assume that the problem is in another location.

I also tried to reset the PID without success. The car will start when the G28 is unplugged, and it runs fine with the G28 connected. However the intermittent misfire issue still occurs at higher RPM. The coolant sensor (G62) even when unplugged, still shows a temperature of -49c. Also, i noticed that the oil pressure gauge in the cockpit is showing 2 bar while 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 eliminated everything else. However, i'm afraid that i might have missed something. If anyone has suggestions, please chime in! TIA!

3. Fuel Pump

The fuel pump in the g28 receives 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 which is why you can easily locate one at a wrecking yard or from a 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 has to know the position and speed of the crankshaft to make a decision about timing of the fuel injectors, etc. It uses a Crank Position Sensor G4 and an Engine Speed Sensor G28 to achieve this. If you have a problem with either of these sensors, the diagnostic scanner will show codes that could cause an engine shutdown.

Some of the symptoms of a failed G28 sensor are an inaccurate rev counter for the gearbox and Audi Key Fobs gears that shift faster than normal and/or misfiring when in gear. If you experience any of these problems, it is most likely that your sensor is deteriorating and requires replacement. The good news is that they are quite affordable and easy to find particularly in the case of the Bosch unit which is what we have. If you prefer, GM's version of this part would be an option.

5. Tachometer

A failing engine sensor could cause a number of problems in your car. It's a vital component of the Audi's transmission because it communicates to the ECU about how fast or slow the car's crankshaft is turning. When this sensor fails, it could affect the performance of the transmission and the other car's components.

The G5 engine sensor is located at the outskirts of the transmission, over the flywheel ring. It transmits signals via an uncolored wire to the ECU pin T55/49. The ECU then processes this signal to control fuel, timig, and boost as well as 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. Also, you can 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 as well as pin T26a/12. You should observe approximately 1000 ohms resistance between these two points. This is a common feature across the audi spare keys 80-100-200-RS2 series, starting from the 1985 MC all the way up to the 1997 UrS AN and the 1995 RS2 Du You may also find some good ones in wrecking yards.