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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 located at the edge of transmission over the flywheel gear. It sends a message to the ECU via an uncolored wire T55/49, then to the tachometer in the instrument cluster.

1. Engine Speed Sensor

Located on the edge of the transmission, above the flywheel ring gear G28 Engine Speed Sensor sends an electrical signal to ECU pin T55/49 through an uncolored wire. The ECU then utilizes this information to regulate the flow of fuel, timig and boost. It also sends an indication to the G5 Tachometer within the instrument cluster.

The sensor is used 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 where the camshaft lies in order to activate the spark and injectors.

If this sensor fails, the ECU will display an error code P00160. This means that the Crank Shaft is out of line with the Intake Camshaft. It could also indicate the possibility of a chain stretch or jump in the chain link of the upper chain of timing. However, the code won't appear on its own without additional information from other sensors (G4 and G40).

It's a bit tricky to test as there are various pins on the connector, and each has its own functions. The best method replacement key for audi doing this is by measuring the resistance between the ECU and replaced the sensor. When the sensor is functional, it should read approximately 1000 ohms. Look for signs of coolant or oil in the connector bay if you are experiencing problems with this part.

2. Injectors

Yesterday, when i was accelerating to the fullest speed from highway paytoll, i experienced a big cut in power like the engine is out of gas or the injectors are not firing at all. I pulled out the spark plugs this morning, three were soaked with gasoline and the fourth was unclean. When I start the engine, there are no sparks i put tissue on top of each injector hole and the 3 drenched with gazoline leap out, however the 4th stay shut. I checked the ground connection of ECU pins 14,30 and 48/55. I found zero ohm. I think the issue is in another location.

I also tried to reset the PID without success. The car will start when the G28 is disconnected, replaced but it works fine when the G28 connected. However the intermittent misfire issue persists at higher RPM. The coolant temperature sensor (G62) shows the wrong temperature of that is -49c even after unplugging it. Also i noticed that the oil pressure gauge in the cockpit is showing 2 bar, whereas the actual pressure is 0.0 when i rev the engine.

I'm not certain what to do, i believe that i've ruled out everything else. I'm worried that i might have missed something. If anyone has any suggestions, please share them! TIA!

3. Fuel Pump

The fuel pump on the g28 is activated by a signal from the RPM sensor. The GM-style transmitter is identical to the G4 sender and both work on the 80,100,200, UrS, and RS2 vehicles. You can easily find a spare in a wrecking shop or parts store. Testing them is easy to do - just put your DMM in resistance mode and take measurements between pins 1 (with the bump on the connector's end up) and 2 (2nd from the left on the black connector's end). They should be infinite Ohms.

4. ECU

Our 20vt turbo (3B AAN, ABY, and ADU) engines have an ECU that needs to be aware of the speed and position of the crankshaft to make a decision about timing of the fuel injector, for example. To do this, it uses a Crank Position Sensor (G4) and an Engine Speed Sensor (G28). If you are experiencing issues with either one of these, the diagnostic scanner will display codes that could lead to the engine shutting down.

The signs of a failed G28 sensor include an inaccurate gearbox rev counter, gears shifting quicker than normal and/or a misfire when you're in gear. If you are experiencing any of these issues, it is most likely that your sensor is failing and should be replaced. They're cheap and easy to find particularly if they're an Bosch model like ours. Alternatively, GM's version of this part would be an option.

5. Tachometer

A damaged engine sensor could cause a myriad of issues in your car. It's a crucial component of the transmission in your Audi since it sends information to the ECU on how fast or slow the engine of the car 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 and sends a signal to the ECU at pin T55/49 via a grey wire. The ECU is then able to process this signal to control fuel, timig and boost as well as transmitting it to the G5 Tachometer located in the instrument cluster. You can test the sensor for failure by checking continuity between it and the tachometer, between the ECU pin T55/49 and the instrument cluster connection on pin T6a/1 (trace [79]) and between pin T6a/1 and the instrument cluster pin T26a/12. You should observe approximately 1000 ohms resistance between those points. This part is common across the Audi 80-100-200-RS2 range, beginning with the 1985 MC and up to the 1997 UrS An and 1995 RS2 DU, so you might find them in wrecking yards.