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How to Replace an audi a5 key fob G28 Engine Speed Sensor

Charles the Humble Technician teaches how to replace the G28 Engine Speed Sensor. The sensor is located at the edge of transmission, above the flywheel gear. It transmits a signal to the ECU via an uncolored wire (T55/49), then to the tachometer within the instrument cluster.

1. Engine Speed Sensor

The sensor is located at the edge of the transmission just above the flywheel ring gear the G28 Engine Speed Sensor sends a signal to ECU pin T55/49 using an uncolored wire. The ECU then utilizes this information to regulate fuel, timig and boost. It also sends signals to the G5 tachometer in the instrument cluster.

The sensor serves as a reference point to connect with the G40 Camshaft Position Sensor. The ecu has to know when the crankshaft has reached TDC and also the location of the camshaft in order to activate the spark and injectors.

If this sensor fails, the ECU will throw the P00160 error, which means the Crank Shaft and Intake Camshaft are not in sync and could indicate 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).

It is a little tricky to test because there are several 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. When the sensor is operational, it should read approximately 1000 ohms. If you are having problems with this sensor, look for evidence of oil or coolant in the connector bay.

2. Injectors

Yesterday, as i was accelerating off the highway paytoll at maximum speed I noticed a massive decrease in power. It was as if the engine was running out of gas. Or my injectors were not firing. I took out the spark plugs this morning, 3 were soaked in gasoline, and the fourth was dry. When I crank the engine without sparks, i place a tissue on the top of each hole in the injector, the 3 drenched with gazoline pop out, but the 4th one stays closed. I tested the ground connection on ECU pins 14/55, 30/55 and 48/55. I got 0ohm. Therefore, i think the issue is somewhere else.

I also tried to reset the PID without success. The car can start if the G28 is not plugged in and it runs perfectly when it is connected however it is experiencing intermittent misfires at higher RPM. The coolant sensor (G62), even when unplugged, still shows temperatures of -49c. Also, i noticed that the oil pressure gauge in the cockpit is showing 2 bar, whereas the actual pressure is 0.0 if i crank up the engine.

I'm not certain what to do, but i feel i have pretty much ruled out everything else. But i'm worried that i might have missed something. If anyone has suggestions, please share them! TIA!

3. Fuel Pump

The fuel pump in 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 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 at the connector's end facing upwards). They should be infinite ohms.

4. ECU

The ECU in our 20vt turbo (3B AAN ABY) engines must know the position and speed of the crankshaft to determine fuel injector timing, etc. In order to do this it uses a Crank Position Sensor (G4) and an Engine Speed Sensor (G28). If either of these go bad you will get codes on the diagnostic scanner which could cause engine shut down.

Some cost of audi key replacement the signs of a failed G28 sensor are an inaccurate rev counter for the gearbox the gears are shifting faster than normal and/or misfiring when in gear. It is probable that the sensor is failing and needs to be replaced if you experience any of these signs. The good news is that they are very cheap and readily available, especially if you're looking at a Bosch unit like ours. Alternatively, GM's version of this component is a good option.

5. Tachometer

A malfunctioning engine sensor can cause a myriad of issues within your vehicle. It's a crucial component of the transmission of your Audi since it sends information to the ECU on how fast or slowly the car's engine is turning. If the sensor fails, it can cause problems for the transmission, as well as the rest of the car's components.

The G5 engine speed sensor is located on the edge of the transmission, above the flywheel ring gear. It sends a signal to the ECU at pin T55/49, via a grey wire. The ECU uses this signal to control fuel and boost, and also timig. It also relays it to the G5 Tachometer in instrument cluster. You can check the sensor Audi a5 key fob for failure by examining the continuity between it and the tachometer, between the ECU pin T55/49 and the instrument cluster connection via pin T6a/1 (trace [79]) and between T6a/1 and the instrument cluster pin T26a/12. You should observe around 1000 ohms of resistance between those points. This is a typical part across the Audi 80, 100, 200, UrS and RS2 range from 1985 MC until the 1997 UrS AAN and 1995 RS2 ADU. Good ones might be availble in wrecking yards.