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How to Replace an Audi G28 Engine Speed Sensor

Charles the Humble Technician teaches how to replace the G28 Engine Speed Sensor. The sensor is situated on the edge of the transmission just above the flywheel ring gear. It transmits a signal to the ECU via an uncolored wire (T55/49) which is then sent to the tachometer located 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 a signal to ECU pin T55/49 using an uncolored wire. The ECU utilizes this information to control fuel and boost. It also sends a signal to the G5 tachometer inside the instrument cluster.

The sensor is used to link the G40 Camshaft position Sensor. The ecu needs to be aware of when the crankshaft has reached TDC, and the location of the camshaft in order to activate the spark and injectors.

If this sensor fails, the ECU will display a P00160 error code. This means that the Crank Shaft is out of alignment with the Intake Camshaft. It could also indicate an issue with the chain or a jumpy chain link in the upper chain. However the code will not be displayed on its own without additional information from other sensors (G4 and G40).

Testing is a bit challenging as there are two different pins for the connector and they serve different purposes but the best method of testing it is by measuring resistance between the sensor and the ECU. It should read about 1000 ohms if the sensor is operating at its maximum. If you are having problems with this component, look for evidence of oil or coolant in the connector bay.

2. Injectors

Yesterday, while accelerating at full speed from the highway paytoll, I experienced an abrupt drop in power like the engine is running out of gas or the injectors are not firing any more. I took out the spark plugs this morning, 3 were soaked with gasoline and the fourth was dry. I placed a tissue over each injector hole, and when i turn the engine on without sparks, the three that have gazoline pop right out. The 4th one remains closed. I inspected the ground connection on ECU pins 14/55, 30/55 and 48/55. I got zero Ohm. I assume that the problem is elsewhere.

I also tried to reset PID but without success. audi keyfob 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 temperature sensor for coolant (G62) shows the wrong temperature value of -49c, even if I unplug it. Also i noticed that the gauge for oil pressure in the cockpit shows 2 bar, whereas the actual pressure is 0.0 when i rev the engine.

I'm not sure what to do. I feel like i've pretty much ruled everything else out. 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 is activated by a signal sent from the RPM sensor. The GM-style transmitter is similar to the G4 sender and works on the 80,100,200, UrS, and RS2 vehicles. You can easily locate an extra in a wrecking shop or a parts store. Test them out - put your DMM in resistance mode and measure the resistance between pins 1 (with the bump on the connector's side up) and 2 (2nd from left on the black connector's end). They must be infinite Ohms.

4. ECU

Our 20vt turbo (3B AAN, ABY and ADU) engines have an ECU that needs to know the position and speed of the crankshaft in order to make decisions regarding fuel injector timing etc. In order to do this it uses a Crank Position Sensor (G4) and an Engine Speed Sensor (G28). If you encounter a problem with either of these, the diagnostic scanner will display the codes that could trigger the engine shutting down.

Some of the signs of a failing G28 sensor are an inaccurate rev counter in the gearbox and gears that shift faster than normal and/or misfiring when you're in gear. If you are experiencing any of these issues it is most likely that your sensor is failing and needs replacing. The good news is that they are very affordable and readily available particularly in the case of a Bosch unit which is what ours are. Alternately, the GM version of this unit is also a good choice.

5. Tachometer

A damaged engine sensor could cause a number of problems in your car. It's an essential component of the transmission in your Audi since it sends information to the ECU on how fast or slowly the car's engine is turning. If this sensor fails, it could affect the performance of the transmission as well as the other car's components.

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

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Pub: 16 May 2024 23:10 UTC

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