How to Replace an Audi G28 Engine Speed Sensor
Charles the Humble Technician teaches you how to replace the G28 Engine Speed Sensor. The sensor is located near the edges of the transmission, above the flywheel ring gear. It sends a message to the ECU via a grey wire T55/49, then to the tachometer in 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 signals through the grey wire to pin T55/49. The ECU uses this information to control the amount of fuel and boost. It also sends an indicator to the G5 Tachometer in instrument cluster.
The sensor serves as a reference for comparing with the G40 Camshaft Position Sensor. The ecu has to know when the crankshaft reached TDC and also where the camshaft lies to trigger the spark and injectors.
If this sensor fails, the ECU will display an error code P00160. This indicates that the Crank Shaft is not in alignment with the Intake Camshaft. It could also be a sign of the possibility of a chain stretch or jumped chain link in the upper chain of timing. The code won't show without the additional information provided by other sensors (G4 or G40).
It is a little tricky to test as there are various pins on the connector, and each has its own functions. The most effective method to test it is by measuring the resistance between the ECU and the sensor. It should read about 1000 ohms if the sensor is operating at its maximum. If you're experiencing issues with this sensor, look for evidence of oil or coolant in the connector bay.
2. Injectors
Yesterday, while accelerating from the highway paytoll at full speed I noticed a significant reduction in power. It was as if the engine had run out of gas. Or my injectors were not firing. This morning i pull out the spark plugs, three were soaked with gazoline and the fourth one was dry. When I start the engine, there are no sparks i put tissue on top of each injector hole, the 3 drenched with gazoline pop out, but the 4th one stays closed. I tested the ground connection of ECU pins 14,30, and 48/55. I found zero ohm. Therefore, i think the issue is in another place.
audi a4 spare key tried to reset PID but without success. The car can start if the G28 is unplugged and runs fine when it is connected but it still has intermittent misfire issues at higher RPM. The coolant sensor (G62), even if it is not plugged in, shows a temperature of -49c. Also, i noticed that the gauge for oil pressure in the cockpit shows 2 bar, whereas the actual pressure is 0.0 when i rev the engine.
I'm not certain what to do, but i feel i have pretty much completely ruled out all other possibilities. I'm afraid i may have missed something. Please let me know should you have any suggestions! TIA!
3. Fuel Pump
The fuel pump in the g28 is activated by a signal sent by the RPM sensor. The GM-style sender is the same as 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 junkyard or in a local parts store. Testing them is easy by putting 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 side). They should be infinite Ohms.
4. ECU
Our 20vt turbo (3B AAN, ABY and ADU) engines have an ECU that has to know the position and speed of the crankshaft to make a decision about fuel injector timing 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 show codes that could lead to an engine shut down.
A failing G28 sensor could cause an inaccurate gearbox speed counter, a gearbox that shifts more quickly than normal, and/or a misfire while in the gear. If you are experiencing any of these issues, it is likely your sensor is going bad and requires replacement. The good news is they are very cheap and readily available, especially in the case of an Bosch sensor, which is what we have. Alternately, the GM version of this part is also a good choice.
5. Tachometer
A malfunctioning engine sensor can cause a number of problems in your car. It's an essential component of the transmission in your Audi, as it transmits information to the ECU regarding how fast or slow the car's engine is spinning. This sensor could cause the transmission to fail and other components of the car to be affected.
The G5 engine speed sensor is located at the edge of the transmission just above the flywheel ring gear. It transmits a signal to the ECU at pin T55/49 through 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 located in the instrument cluster. You can test the sensor for any failure by checking the continuity between it and the tachometer. You can also check continuity between ECU pin T55/49 and the instrument cluster connection via pin T6a/1 (trace [79]) and between pin T6a/1 and the instrument cluster pin T26a/12. You should detect an average resistance of 1000 ohms between these points. This is a common feature across the Audi 80-100-200-RS2 series, starting beginning with the 1985 MC and up to the 1997 UrS AN and the 1995 RS2 DU So, you may find them in wrecking yards.