How to Replace an Audi G28 Engine Speed Sensor
Charles the Humble Technician shows you how to replace the G28 Engine Speed Sensor. This sensor is located at the top of the transmission above the flywheel ring gear. It sends a message to the ECU through the grey wire T55/49 and 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 sends a signal via the grey wire to pin T55/49. The ECU uses this information to control fuel and boost. It also sends a signal to the G5 tachometer inside the instrument cluster.
The sensor is used to correlate the G40 Camshaft position Sensor. The ecu needs to be aware of 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 a P00160 code which means the Crank Shaft and Intake Camshaft aren't in sync and could indicate chain stretch or a jumped link on the upper chain of timing. The code won't show without the additional information provided by other sensors (G4 or G40).
It can be a bit difficult to test because there are different pins on the connector, and each has its own functions. The best way to do it is by measuring the resistance between the ECU and the sensor. If the sensor is operational, it should be reading about 1000 ohms. Examine for evidence of coolant or oil in the connector bay if you have issues with this part.
2. Injectors
Yesterday, when accelerating from highway paytoll at maximum speed I noticed a significant decrease in power. It was as if the engine was running out of gas. Or my injectors were not firing. In the morning, i removed the spark plugs. Three were drenched with gazoline the fourth one 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 of ECU pins 14,30, and 48/55. I got 0ohm. So i assume the problem is elsewhere.
I also tried to reset the PID without success. The car can start if the G28 is disconnected and is running fine when it is plugged in however it has intermittent misfire issues 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 shows 2 bar, whereas 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. But i am 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 can be activated by a signal from the RPM sensor. The GM-style sensor is the same as the G4 and both are used in the 80 100 200, UrS and RS2 cars so you can easily find one at a wrecking yard or at a parts store. Test them out by putting your DMM in resistance mode and take measurements between pins 1 (with the bump on the connector's end up) and 2 (2nd from the left on the black end of the connector). 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 in order 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 either of these goes badly, you will see codes on the diagnostic scanner that could cause engine shut down.
A failing G28 sensor can cause an inaccurate speed counter for your gearbox, a gearbox that shifts more quickly than normal, or a misfire while in the gear. If you experience any of these problems, it is likely your sensor is deteriorating and should be replaced. They're cheap and easy to find, especially if they're an Bosch unit like ours. If you prefer, GM's version of this component is an option.
5. Tachometer
A malfunctioning engine speed sensor could be the reason behind a slew of issues with your vehicle. It's a crucial component of the transmission of your Audi, as it transmits information to the ECU regarding how fast or slowly the engine is spinning. If what to do if you lose your audi key fails, it will cause problems for the transmission, as well as the other car's components.
The G5 engine speed sensor is located at the outside of the transmission, above the flywheel ring gear and sends a signal directly to the ECU at pin T55/49 via an uncolored wire. The ECU uses this signal to regulate the amount of fuel and boost, as well as timig. It also transmits it to the G5 Tachometer located in the instrument cluster. You can determine if the sensor is in failure by examining the continuity of 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 as well as pin T26a/12. You should observe approximately 1000 ohms of resistance between those two pins. This is a common feature across the Audi 80-100-200-RS2 range, from the 1985 MC all the way up to the 1997 UrS AN and 1995 RS2 DU, so you might find good ones in wrecking yards.