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. This sensor is situated on the outside of the transmission, above the flywheel gear. It sends a message to the ECU through a grey wire T55/49, then to the tachometer located on the instrument cluster.
1. Engine Speed Sensor
The grey wire is located at the edges of the transmission, just above the flywheel ring. The sensor transmits an electrical signal through the grey wire to pin T55/49. The ECU then uses this information to control the flow of fuel, timig and boost. It also sends a signal to the G5 Tachometer located in the instrument cluster.
The sensor is used as a reference point to connect with the G40 Camshaft Position Sensor. The ecu must be aware when the crankshaft is TDC and where the camshaft is located so that it can activate spark and injectors in the right way.
If this sensor fails, the ECU will display the P00160 error, which means the Crank Shaft and Intake Camshaft aren't in sync, possibly indicating the chain is stretched or a jump link on the upper chain of timing. The code will not appear without the additional information provided by other sensors (G4 or G40).
It's a bit tricky to test because there are different pins on the connector and each one has different functions. The most effective method to test it is to measure the resistance between the ECU and the sensor. If the sensor is operational, it should be reading around 1000 ohms. Check for signs of coolant, or oil in the connector bay if you are experiencing issues with this part.
2. Injectors
Yesterday, when accelerating from highway paytoll at full speed, i noticed a huge drop in power. It was like the engine had run out of gas. Or my injectors weren't firing. I took out the spark plugs this morning, three were soaked in gasoline, and the fourth was dry. I put a piece of tissue over each injector hole and when I start the engine with no sparks, the 3 that have gazoline pop right out. The 4th one stays shut. I tested the ground connection on ECU pins 14/55/30/55/48/55/14/55/48/ I got zero Ohm. Therefore, i think the issue is in another place.
I also tried to reset the PID without success. The car will start when the G28 is disconnected, but it works fine when the G28 plugged in. However, the intermittent misfire problem still occurs at higher RPM. The coolant sensor (G62), even when unplugged, still shows an ice temperature of -49c. 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 don't know what to do. I believe that I've all other possibilities out. I'm worried that i might have missed something. Let me know If you have any suggestions! TIA!
3. Fuel Pump
The fuel pump on the g28 is activated by a signal by the RPM sensor. The GM-style sensor is identical to the G4 and both function in the 80, 100, 200, UrS and RS2 cars which is why you can easily locate one at a junkyard or in a local parts store. It is simple to test them - just put your DMM into resistance mode and measure the distance between pins 1 and 2 (with the bump at the connector end facing up). They must be infinite Ohms.
4. ECU
Our 20vt turbo (3B, AAN, ABY and ADU) engines are equipped with an ECU that has to know the position and speed of the crankshaft to make a decision about timing of the fuel injectors, etc. It utilizes a Crank Position Sensor G4 and an Engine Speed Sensor G28 to accomplish this. If you encounter a problem with either of these sensors, the diagnostic scanner will display codes that could cause an engine shut down.
A failing G28 sensor can cause an inaccurate speed counter for your gearbox, a gearbox that shifts faster than normal, or a misfire while in gear. It is likely that the sensor is failing and needs to be replaced if you experience any of these symptoms. The good news is that they are very cheap and easily accessible particularly in the case of the Bosch model, like ours. Alternatively, GM's version of this part would be a good option.
5. Tachometer
A malfunctioning engine sensor can cause a number of problems in your vehicle. It's a crucial component of the transmission of your Audi since it sends information to the ECU about how fast or slowly the car's engine is turning. When this sensor fails, it will disrupt the performance of the transmission, as well as the rest of the car's components.
The G5 engine speed sensor is situated on the edge of the transmission just above the flywheel ring gear and sends a signal to the ECU at pin T55/49 through an uncolored wire. The ECU uses this signal to regulate fuel and boost, and also timig. It also relays it to the G5 Tachometer in instrument cluster. You can test for sensor failure by checking continuity from the sensor to the tachometer. Additionally, you can examine the continuity between pins T55/49 of the ECU and pin T6a/1 of the instrument cluster (trace [79trace [79]) and between pin T6a/1 as well as pin T26a/12. Read Far more should show around 1000 ohms of resistance between those two pins. This is a common part 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 ones might be availble in wrecking yards.