How to Replace an Audi G28 Engine Speed Sensor
In this video, Charles the Humble Mechanic shows 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 via an uncolored wire T55/49, then to the tachometer on the instrument cluster.
1. Engine Speed Sensor
Located on the edge of the transmission, above the flywheel ring gear, the G28 Engine Speed Sensor sends a signal to ECU pin T55/49 using a grey wire. The ECU uses this information to regulate boost and fuel. It also sends an indicator to the G5 Tachometer in instrument cluster.
The sensor is used to connect the G40 Camshaft position Sensor. The ecu needs to know when the crankshaft reached TDC and also where the camshaft lies to trigger the spark and injectors.
If this sensor fails when it fails, the ECU will display an error code P00160. This means that the Crank Shaft is out of alignment with the Intake Camshaft. It could also indicate a chain stretch or a jumpy chain link in the upper chain. The code won't appear without the additional information provided by other sensors (G4 or G40).
Testing is a bit challenging since there are two connector pins and they serve different purposes however the best method to test it is to measure the resistance between the sensor and the ECU. It should read around 1000 ohms when the sensor is at full operation. Look for signs of coolant or oil in the connector bay if you are experiencing problems with this part.
2. Injectors
Yesterday, while accelerating at full speed from the highway paytoll, I experienced a big cut in power like the engine is out of gas or the injectors are not firing any more. I pulled out the spark plugs this morning and found that 3 were soaked with gasoline and the fourth was dry. When i crank the engine with no sparks, I put a piece of tissue on the top of each hole in the injector and the 3 that were drenched in gazoline pop out, but the 4th stays closed. I checked the ground connection on ECU pins 14/55,30/55 and 48/55 I got zero Ohm. Therefore, i think the issue is somewhere else.
I also tried to reset the PID but with no luck. The car will start when the G28 is unplugged and is running fine when it is connected, but still has the intermittent misfire issue at higher RPM. The coolant sensor (G62) even if it is not plugged in, shows temperatures of -49c. I also noticed that the oil gauge in the cockpit shows 2 bars when the actual pressure is zero.
I don't know what to do. I believe that I've ruled everything else out. But i'm worried that I may have missed something. Let me know should you have any suggestions! TIA!
3. Fuel Pump
The fuel pump of the g28 gets a signal from the RPM sensor. The GM-style transmitter is identical to the G4 sender and both work on the 80,100,200, UrS, and RS2 vehicles. You can easily find a spare in a wrecking shop or a parts store. Testing them is easy to do - just put your DMM in resistance mode and measure the resistance between pins 1 (with the bump on the connector end up) and 2 (2nd from left on the black connector's end). They must be infinite Ohms.
4. ECU
The ECU of our 20vt turbo (3B AAN ABY ADU) engines must be aware of the position and speed the crankshaft to determine timing of the fuel injector, etc. audi lost key makes use of a Crank Position Sensor G4 and an Engine Speed Sensor G28 to achieve this. If either of these sensors go bad you will get codes on the diagnostic scanner which could cause engine shut down.
The signs of a malfunctioning G28 sensor include an inaccurate rev counter for the gearbox, gears shifting quicker than normal and/or misfiring when in gear. If you experience any of these issues, it is likely your sensor is failing and requires replacement. They're cheap and easy to find, especially when they're a Bosch model like ours. Alternatively, the GM version of this component is also a good choice.
5. Tachometer
A malfunctioning engine speed sensor could be the cause of a slew of problems in your car. It is a crucial part of your Audi's transmission, as it sends information to the ECU about how the car's crankshaft is turning. This sensor could cause the transmission to malfunction and other car components to be affected.
The G5 engine sensor is located at the outskirts of the transmission, just above the flywheel ring. It transmits an electrical signal through a gray wire to the ECU pin T55/49. The ECU then processes the signal to control fuel, timig, and boost as well as sends it on to the G5 tachometer in the instrument cluster. You can check for sensor failure by examining the 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 [79]) and between pin T6a/1 and pin T26a/12. It 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 until the 1997 UrS AAN and 1995 RS2 ADU so good parts could be found in wrecking yards.