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 located on the edge of the transmission, above the flywheel ring gear. It transmits a signal the ECU via an uncolored wire (T55/49) which is then sent to the tachometer located in the instrument cluster.
1. Engine Speed Sensor
The sensor is located at the edge of the transmission above the flywheel ring gear, the G28 Engine Speed Sensor sends signals to ECU pin T55/49 using the grey wire. The ECU then utilizes this information to regulate the flow of fuel, timig and boost. It also sends an indicator to the G5 Tachometer located in the instrument cluster.
The sensor is used to correlate the G40 Camshaft position Sensor. The ecu needs to know when the crankshaft is TDC and the location of the camshaft so it can start spark and injectors in the right way.
If this sensor fails the ECU will throw an error code P00160 which indicates that the Crank Shaft and Intake Camshaft aren't in sync and possibly indicating the chain stretching or a jump link on the upper timing chain. The code won't show without the additional information supplied by other sensors (G4 or G40).
It is a little tricky to test because there are different connector pins, and they all have different functions. The best way to do it is to measure the resistance between the ECU and the sensor. When the sensor is fully functional, it should read about 1000 ohms. Check for signs of coolant, or oil in the connector bay if you have problems with this part.
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 injectors are not firing at all. I took out the spark plugs this morning, 3 were drenched in gasoline and the 4th was dry. I placed a tissue over each injector hole and when I start the engine without sparks, the ones with gazoline jump out. The 4th one stays closed. I inspected the ground connection on ECU pins 14/55/30/55/48/55/14/55/48/ I got 0ohm. I think the issue is in another location.
I also tried to reset the PID with no success. The car can start when the G28 is unplugged and is running fine when it is plugged in but it still is experiencing intermittent misfires at higher RPM. The temperature sensor for coolant (G62) shows the wrong temperature value of -49c, even if I unplug it. I also noticed that the oil gauge in the cockpit shows 2 bars when the actual pressure is zero.
I'm not sure what to do, but i feel i have pretty much eliminated everything else. But i'm worried that i might have missed something. Let me know If you have any suggestions! TIA!
3. Fuel Pump
The fuel pump in the g28 receives a signal from the RPM sensor. The GM-style sensor is identical to the G4 and they both work in the 80 100 200, UrS and RS2 cars which is why you can easily locate one at a salvage yard or at a parts store. It is easy to test them - simply put your DMM into resistance mode and determine the distance between pins 1 and 2 (with the bump on the connector's edge facing up). They must be infinite Ohms.
4. ECU
Our 20vt turbo (3B AAN, ABY, and ADU) engines are equipped with an ECU that needs to know the speed and position of the crankshaft to make decisions regarding 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 of these sensors, the diagnostic scanner will display codes that could lead to an engine shut down.
The signs of a failed G28 sensor are an inaccurate gearbox rev counter the gears are shifting faster than normal, and/or a misfire when you're in gear. If you have any of these issues it is likely that your sensor is failing and should be replaced. They're inexpensive and easy to locate particularly if they're an Bosch model like ours. Alternatively, GM's version of this component is an option.
5. Tachometer
A malfunctioning engine sensor can cause a myriad of issues within your vehicle. It's an essential component of the transmission of your Audi since it sends information to the ECU about how fast or slowly the car's engine is spinning. When 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 on the outside of the transmission above the flywheel ring gear and sends a signal to the ECU at pin T55/49 through an uncolored wire. The ECU is then able to process this signal to regulate fuel, timig, and boost as well as transmitting it to the G5 tachometer in the instrument cluster. You can determine if the sensor is in failure by examining the continuity from the sensor to the tachometer. Also, you can examine the continuity between pins T55/49 of the ECU and pin T6a/1 of the instrument cluster (trace [79]), and between pin T6a/1 as well as pin T26a/12. There should be a resistance of approximately 1000 ohms in these areas. This is a common component across the Audi 80 100, 200, UrS and RS2 range from 1985 MC through the 1997 UrS AAN and 1995 RS2 ADU, so the best parts could be found in wrecking yards.