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 located at the edge of transmission just above the flywheel gear. It transmits a signal to the ECU through the grey wire T55/49 and then to the tachometer on 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 via an uncolored wire. The ECU then utilizes this information to regulate fuel, timig and boost. It also sends a signal to the G5 Tachometer located in the instrument cluster.
The sensor is used to connect with the G40 Camshaft position Sensor. The ecu has to know when the crankshaft has reached TDC, and the location of the camshaft to trigger the spark and injectors.
If this sensor fails, the ECU will show the P00160 error, which means the Crank Shaft and Intake Camshaft are out of 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 since there are several connector pins, and each one has different functions. The most effective method to test it is by measuring the resistance between the ECU and the sensor. When the sensor is functional, it should read around 1000 ohms. Check for signs of coolant, or oil in the connector bay if there are problems with this part.
2. Injectors
Yesterday accelerating full speed from highway paytoll, I experienced an abrupt drop in power like the engine is out of gas or the injectors are not firing at all. I pulled out the spark plugs this morning and found that 3 were soaked in gasoline, and the 4th was dry. I placed a tissue over each injector hole, and when i start the engine with no sparks, the 3 with gazoline jump out. The 4th one remains closed. I tested the ground connection on ECU pins 14/55,30/55 and 48/55 I get zero Ohm. I'm assuming the issue is in another place.
I also tried to reset PID without success. The car will start if the G28 is not plugged in and it click here runs perfectly when it is connected, but still has intermittent misfire issues at higher RPM. The coolant sensor (G62), even if it is not plugged in, shows an ice temperature of -49c. Also, i noticed that the gauge for oil pressure in the cockpit shows 2 bar while the actual pressure is 0.0 here if i crank up the engine.
I'm not sure what to do. I feel like i've pretty much ruled everything else out. But i am afraid i might have missed something. If anyone has any suggestions, check here please chime in! TIA!
3. Fuel Pump
The fuel pump in the g28 gets a signal from the RPM sensor. The GM-style sensor is the same as the G4 and both function in the 80 100 200, read more UrS and RS2 cars which is why you can easily locate one at a salvage yard or at a 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 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 must be aware of the speed and position of the crankshaft to make a decision about timing of the fuel injector, for example. In order to do this it makes use of a Crank Position Sensor (G4) and an Engine Speed Sensor (G28). If you are experiencing issues with either one of these, the diagnostic scanner will display the codes that could trigger the engine shutting down.
A damaged G28 sensor can cause an inaccurate speed counter for the gearbox, a gearbox that shifts faster than normal, or an unfire when in the gear. It is likely that the sensor is failing and requires to be replaced if you experience any of these signs. The good news is they are very cheap and readily available particularly when you're looking at the Bosch unit which is what we have. Alternately, GM's version this part would be an option.
5. Tachometer
A damaged engine sensor could cause a number of problems in your vehicle. It's a vital component of the Audi's transmission since it relays information to the ECU about how fast or slow the car's crankshaft is spinning. If the sensor fails, it will cause problems for the transmission and the rest of the car's components.
The G5 engine speed sensor is located check here on the edge of the transmission above the flywheel ring gear and sends a signal to the ECU at pin T55/49 via a grey wire. The ECU then uses and processes this signal to control the flow of fuel, timig and boost and then transmitting it to the G5 tachometer inside the instrument cluster. You can check the sensor for failure by checking continuity between it and the tachometer, between ECU pin T55/49 and the instrument cluster connection via pin T6a/1 (trace [79trace [79]) and between T6a/1 and the instrument cluster pin T26a/12. It should show around 1000 ohms of resistance between those two pins. This is a common part that is found across the Audi 80, 100, 200, UrS and RS2 range from 1985 MC until the 1997 UrS AAN and 1995 RS2 ADU so good ones could be available in wrecking yards.