How to Replace an Audi G28 Engine Speed Sensor
Charles the Humble Technician shows you how to replace the G28 Engine Speed Sensor. The sensor is situated on the edge of the transmission just above the flywheel ring gear. It sends a signal to the ECU via the grey wire (T55/49), then to the tachometer located in the instrument cluster.
1. Engine Speed Sensor
The grey wire is situated on the edge of 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 an indication to the G5 Tachometer located in the instrument cluster.
The sensor is used to connect with the G40 Camshaft position Sensor. The ecu needs to know when the crankshaft is TDC and where the camshaft is so it can activate spark and injectors accordingly.
If this sensor fails, the ECU will display an error code P00160. This indicates that the Crank Shaft is not in line with the Intake Camshaft. It could also indicate an issue with the chain or a jumped chain link in the upper timing chain. However, the error code won't appear on its own, without additional information from other sensors (G4 and G40).
It is a little tricky to test because there are different connector pins, and each one has different functions. The most effective method to test it is to measure the resistance between the ECU and the sensor. It should read about 1000 ohms if the sensor is operating at its maximum. If you are having problems with this sensor, look for signs of coolant or oil in the connector bay.
2. Injectors
Yesterday, when accelerating from highway paytoll at a high speed I noticed a significant reduction in power. It was like the engine had run out of gas. Or audi advanced key weren't firing. In the morning, i removed the spark plugs. Three were drenched in gazoline, the fourth was dry. I put tissue over each injector hole and when i start the engine without sparks, the 3 that have gazoline pop right out. The fourth one remains closed. I tried to test the ground connections of ECU pins 14,30 and 48/55. I found zero ohm. I assume that the problem is in another location.
I also tried to reset the PID but with no luck. The car will start if the G28 is unplugged and runs fine when it is connected, but still has intermittent misfire issues at higher RPM. The temperature sensor for coolant (G62) shows the wrong temp value that is -49c even after unplugging it. Also, i noticed that the oil pressure gauge in the cockpit is showing 2 bar when the actual pressure is 0.0 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'm worried that i might have missed something. Please let me know if you have any ideas! 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 identical to the G4 and both are used in the 80, 100 200, UrS and RS2 cars which is why you can easily locate one at a wrecking yard or in a local parts store. It is easy to test them: simply switch your DMM into resistance mode and determine 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 have an ECU that needs to be aware of the speed and position of the crankshaft to make decisions about fuel injector timing etc. To do this, it uses a Crank Position Sensor (G4) and an Engine Speed Sensor (G28). If either of these goes wrong, you will receive codes on the diagnostic scanner which could cause engine shut down.
Some of the signs of a failed G28 sensor are an inaccurate rev counter in the gearbox the gears are shifting faster than normal and/or a misfire when in gear. It is possible that your sensor is failing and needs to be replaced if you encounter any of these symptoms. The good news is that they are very affordable and easily accessible, especially when you're looking at an Bosch unit which is what ours are. Alternately, the GM version of this component is also a great option.
5. Tachometer
A faulty engine speed sensor could be a cause for a slew of issues in your car. It is a crucial part of the Audi's transmission because it communicates to the ECU about how the car's crankshaft is turning. If the sensor fails, it could disrupt the performance of the transmission and the other car's components.
The G5 engine sensor is located at the edge of transmission, above the flywheel ring. It sends a signal via an uncolored wire to the ECU pin T55/49. The ECU utilizes this signal to control the amount of fuel and boost, and also timig. It also transmits it to the G5 Tachometer in 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 to pin T6a/1 (trace [79trace [79]) and between T6a/1 and the instrument cluster pin T26a/12. You should detect an average resistance of 1000 ohms between these points. This is the same across the Audi 80-100-200-RS2 model, ranging beginning with the 1985 MC and up to the 1997 UrS AN and the 1995 RS2 DU, so you might find some good ones in wrecking yards.