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How to Replace an Audi G28 Engine Speed Sensor
In this video, Charles the humble mechanic demonstrates how to replace the G28 engine speed sensor. The sensor is situated near the edges of the transmission, above the flywheel ring gear. It transmits a signal to the ECU through the grey wire T55/49 and then to the tachometer on the instrument cluster.
1. Engine Speed Sensor
The grey wire is situated on the edge of transmission, directly above the flywheel ring. This sensor sends a signal via the grey wire to pin T55/49. The ECU uses this information to regulate boost and fuel. It also sends an indication 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 be aware of 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 display a P00160 error code. This means that the Crank Shaft is not in alignment with the Intake Camshaft. It could also indicate an issue with the chain or a jumped chain link in the upper chain. However the code will not appear on its own without additional information from other sensors (G4 and G40).
Testing can be a bit difficult because there are two connector pins, and they have different functions but the most effective method of testing it is to measure resistance between the sensor and the ECU. When the sensor is fully functional, it should read approximately 1000 ohms. Check for signs of coolant, or oil in the connector bay if you have issues with this component.
2. Injectors
Yesterday, when accelerating from highway paytoll at a high speed I noticed a significant drop in power. It was as if the engine had run out of gas. Or, my injectors were not firing. Today, i pulled out the spark plugs, three were drenched in gazoline, the 4th one was dry. I placed a tissue over each hole in the injector and when i start the engine with no sparks, the ones that have gazoline pop right out. The fourth one remains closed. I checked the ground connection on ECU pins 14/55/30/55/48/55/14/55/48/ I get 0ohm. I'm assuming the issue is elsewhere.
I also tried to reset PID but without success. The car is able to start if the G28 is unplugged and runs fine when it is plugged in, but still is experiencing intermittent misfires at higher RPM. The coolant sensor (G62), even when it is unplugged, shows an ice temperature of -49c. I also noticed that the oil gauge in the cockpit shows 2 bars while the actual pressure is 0.
I don't know what to do. I feel like i've pretty much eliminated everything else. I'm worried that i might have missed something. If anyone has any suggestions, please let me know! TIA!
3. Fuel Pump
The fuel pump of the g28 receives signals from the RPM sensor. The GM-style transmitter is similar to the G4 sender and both work on the 80,100,200, UrS, and RS2 vehicles. You can easily find an extra in a wrecking shop or a parts store. It is easy to test them - just put your DMM into resistance mode and measure the distance between pins 1 and 2 (with the bump on the connector's edge facing up). They should be infinite Ohms.
4. ECU
Our 20vt turbo (3B AAN, ABY, and ADU) engines have an ECU that must be aware of the speed and position of the crankshaft to make a decision about timing of the fuel injectors, etc. To accomplish this, it makes use of a Crank Position Sensor (G4) and an Engine Speed Sensor (G28). If either of these goes wrong, you will receive codes on the diagnostic scanner which can cause the engine to shut down.
A failing G28 sensor could result in an inaccurate gearbox speed counter or a gearbox that shifts faster than normal, and/or a misfire while in the gear. It is probable that your sensor is failing and needs to be replaced if you experience any of these signs. The good news is they are very affordable and easy to find, especially in the case of the Bosch unit which is what ours are. Alternatively, the GM version of this component is also a great option.
5. Tachometer
A failing engine speed sensor could be a cause for a slew of problems in your vehicle. It's a vital component of the Audi's transmission because it communicates to the ECU about how the car's crankshaft is rotating. This sensor can cause the transmission to malfunction and other components in the car to be affected.
The G5 engine speed sensor is located at the outside of the transmission just above the flywheel ring gear. It sends a signal directly to the ECU at pin T55/49 through a grey wire. The ECU then uses and processes this signal to regulate the flow of fuel, timig and boost, and also sends it on to the G5 tachometer in the instrument cluster. You can test the sensor for failure by checking continuity between it and the tachometer, between ECU pin T55/49 and the instrument cluster connection via pin T6a/1 (trace [79]) as well as between T6a/1, and the instrument cluster pin T26a/12. You should detect an average resistance of 1000 ohms in these areas. This is a typical part across the Audi 80, 100 200, UrS and RS2 range from 1985 MC through the 1997 UrS AAN and 1995 RS2 ADU so good parts could be found in wrecking yards.