20 Myths About Audi G28: Dispelled
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In this video, Charles the humble mechanic demonstrates how to replace the G28 engine speed sensor. This sensor is located near the transmission's edge, above the flywheel gear. It transmits a signal to the ECU via an uncolored wire T55/49, then to the tachometer on the instrument cluster.
1. Engine Speed Sensor
The grey wire is situated on the outside of the transmission, directly above the flywheel ring. The sensor sends a signal via the grey wire to pin T55/49. The ECU then utilizes this information to regulate the flow of fuel, timig and boost. It also sends an indication to the G5 tachometer inside the instrument cluster.
The sensor serves as a reference to correlate with the G40 Camshaft Position Sensor. The ecu has to be aware of 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 which indicates that the Crank Shaft and Intake Camshaft aren't in sync and possibly indicating chain stretch or a jumped link on the upper timing chain. The code won't appear without the additional information supplied by other sensors (G4 or G40).
Testing is a bit tricky as there are two different pins for the connector and they have different functions but the most effective method to test it is to measure the resistance between the sensor and the ECU. When the sensor is operational, it should read around 1000 ohms. If you're having issues with this component, look for evidence of coolant or oil in the connector bay.
2. Injectors
Yesterday, as i was accelerating off the highway paytoll at full speed I noticed a significant 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 and found that 3 were drenched in gasoline and the fourth was unclean. When i crank the engine without sparks i put tissue on the top of each of the injector holes and the 3 that were drenched in gazoline leap out, however the 4th one stays shut. I checked the ground connection of ECU pins 14,30 and 48/55. I found 0ohm. So i assume the problem is in another place.
I also tried to reset the PID without success. The car is able to start when the G28 is unplugged and runs fine when it is plugged in, but still has the intermittent misfire issue at higher RPM. The temperature sensor for the coolant (G62) shows the wrong temp value -49c even when i unplug it. Also, i noticed that the oil pressure gauge in the cockpit is showing 2 bar while the actual pressure is 0.0 when i rev the engine.
I'm not sure what to do. I think I've eliminated everything else. However, i'm afraid that I might have missed something. If anyone has any suggestions, please let me know! TIA!
3. Fuel Pump
The fuel pump on the g28 is activated by a signal sent from the RPM sensor. The GM-style transmitter is identical to the G4 and both function in the 80 100 200, UrS and RS2 cars so you can easily find one at a junkyard or in a local parts store. Testing them is easy - put your DMM in resistance mode and measure the resistance 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 must be infinite ohms.
4. ECU
The ECU in our 20vt turbo (3B AAN ABY) engines must know the position and speed the crankshaft to determine timing of fuel injectors, etc. It utilizes a Crank Position Sensor G4 and an Engine Speed Sensor G28 to achieve this. If you encounter a problem with either one of these, the diagnostic scanner will display codes that could lead to an engine shutdown.
Some of the symptoms of a failing G28 sensor are an inaccurate gearbox rev counter and gears that shift faster than normal, and/or a misfire when you are in gear. If you are experiencing any of these problems, it is likely that your sensor is going bad and should be replaced. They're inexpensive and easy to locate particularly when they're a Bosch unit like ours. Alternately, GM's version this part is an option.
5. Tachometer
A malfunctioning engine sensor can cause a variety of issues in your vehicle. It's an essential component of your Audi's transmission, because it communicates to the ECU about how fast or slow the car's crankshaft is turning. If this sensor fails, it could cause problems for the transmission and the other car's components.
The G5 engine speed sensor is located at the outside 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 the flow of fuel and boost and also to timigrate. It also transmits it to the G5 Tachometer located in the instrument cluster. You can check the sensor for failure by examining the continuity between it and the tachometer. You can also check continuity between ECU pin T55/49 and the instrument cluster connection to pin T6a/1 (trace [79trace [79]) as well as between T6a/1, and the instrument cluster pin T26a/12. It should show around 1000 ohms of resistance between these two points. This is a standard part that is found across the Audi 80, 100 200, UrS and RS2 range from 1985 MC to the 1997 UrS AAN and 1995 RS2 ADU, so the best ones might be availble in wrecking yards.