How to Replace an Audi G28 Engine Speed Sensor
Charles the Humble Technician shows you how to replace the G28 Engine Speed Sensor. The sensor is situated on the edge of the transmission above the flywheel ring gear. It sends a message to the ECU through the grey wire T55/49 and then to the tachometer located on the instrument cluster.
1. Engine Speed Sensor
The grey wire is located on the outside of the transmission, just above the flywheel ring. The sensor transmits a signal via the grey wire to pin T55/49. The ECU then utilizes this information to regulate the boost, fuel, and timig. It also sends an indicator to the G5 Tachometer within the instrument cluster.
The sensor serves as a reference for comparing with the G40 Camshaft Position Sensor. The ecu must know when the crankshaft reached TDC and also the location of the camshaft so that it can activate the spark and injectors.
If this sensor fails the ECU will display a P00160 code which means the Crank Shaft and Intake Camshaft aren't in sync and possibly indicating the chain is stretched or a jump link on the upper chain of timing. The code won't show without the additional information supplied by other sensors (G4 or G40).
Testing is a bit tricky because there are two connector pins, and they have different functions however the best method to test it is to measure resistance between the sensor and the ECU. It should read about 1000 ohms if the sensor is operating at its maximum. Examine for evidence of coolant or oil in the connector bay if there are issues with this component.
2. Injectors
Yesterday accelerating full speed from highway paytoll i had a big cut in power as if the engine was running out of gas or injectors aren't firing anymore. I took out the spark plugs this morning and found that 3 were soaked in gasoline, and the fourth was unclean. I put a piece of tissue over each injector hole, and when I start the engine without sparks, the three that have gazoline pop right out. The 4th one remains closed. I tested the ground connection of ECU pins 14,30 and 48/55. I got 0ohm. Therefore, i think the issue is somewhere else.
I also tried to reset the PID with no success. The car will start when the G28 is disconnected, but it works fine when the G28 connected. However, the intermittent misfire problem still occurs at higher RPM. The coolant temperature sensor (G62) shows the wrong temp value -49c, even if I unplug it. I also noticed that the oil gauge in the cockpit shows 2 bar but the actual pressure is 0.
I don't know what to do. I think I've ruled everything else out. I'm concerned that i may have missed something. Let me know If you have any suggestions! TIA!
3. Fuel Pump
The fuel pump in the g28 can be activated by a signal by the RPM sensor. The GM-style transmitter is identical to the G4 and both are used in the 80 100, 200, UrS and RS2 cars so you can easily find one at a junkyard or in a local parts store. It is simple to test them - simply put your DMM into resistance mode and measure the distance between pins 1 and 2 (with the bump at the connector's end facing upwards). They must be infinite ohms.
4. ECU
Our 20vt turbo (3B, AAN, ABY and ADU) engines are equipped with an ECU that has to 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 uses a Crank Position Sensor (G4) and an Engine Speed Sensor (G28). If you have a problem with either one of these, the diagnostic scanner will display codes that could cause the engine shutting down.
A malfunctioning G28 sensor could cause an inaccurate speed counter for the gearbox and a gearbox which shifts more quickly than normal, or an unfire when in gear. If you are experiencing any of these problems, it is most likely that your sensor is deteriorating and needs replacing. They are cheap and easy-to-find, especially in the case of an Bosch sensor like ours. Alternatively, GM's version of this component is a good option.
5. Tachometer
A damaged engine sensor could cause a variety of issues within your vehicle. It's an essential component of the transmission of your Audi, as it transmits information to the ECU about how fast or slowly the engine of the car is spinning. When this sensor fails, it can affect the performance of the transmission as well as the rest of the car's components.
The G5 engine sensor is located near the edge of the transmission, over the flywheel ring. It sends a signal via a gray wire to the ECU pin T55/49. The ECU is then able to process the signal to control the flow of fuel, timig and boost, and also transmitting it to the G5 tachometer in the instrument cluster. You can check the sensor for failure by examining the continuity between it and the tachometer, between the ECU pin T55/49 and the instrument cluster connection on pin T6a/1 (trace [79trace [79]) and between pin T6a/1 and the instrument cluster pin T26a/12. You should detect the resistance to be around 1000 ohms between these two points. This is a standard component across the Audi 80 100, 200, UrS and RS2 range from 1985 MC until the 1997 UrS AAN and 1995 RS2 ADU, so the best parts could be found in wrecking yards.