How to Replace an Audi G28 Engine Speed Sensor
In this video Charles the Humble Mechanic demonstrates how to replace the G28 engine speed sensor. The sensor is situated at the top of the transmission just above the flywheel ring gear. It sends a signal to the ECU via the grey wire (T55/49) which is then sent to the tachometer located in the instrument cluster.
1. Engine Speed Sensor
The sensor is located at the edge of the transmission above the flywheel ring gear G28 Engine Speed Sensor sends a signal to ECU pin T55/49 through the grey wire. The ECU then uses this information to control the boost, fuel, and timig. It also sends an indication to the G5 tachometer inside the instrument cluster.
The sensor is used as a reference for comparing with the G40 Camshaft Position Sensor. The ecu must know when the crankshaft is TDC and the location of the camshaft so it can start spark and injectors accordingly.
If this sensor fails, the ECU will show a P00160 code which means the Crank Shaft and Intake Camshaft are out of sync, possibly indicating the chain stretching or a jump link on the upper timing chain. However, the error code won't appear on its own without additional information from other sensors (G4 and G40).
Testing is a bit challenging since there are two connector pins, and they serve different purposes but the most effective method to test it is by measuring resistance between the sensor and the ECU. If the sensor is functional, it should read around 1000 ohms. 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 maximum speed I noticed a massive reduction in power. It was like the engine had run out of gas. Or, my injectors were not firing. In the morning, i removed the spark plugs, three were soaked with gazoline and the fourth one was dry. I put tissue over each hole in the injector and when i start the engine without sparks, the ones with gazoline jump out. The 4th one stays shut. I tried to test the ground connections of ECU pins 14,30, and 48/55. I found zero ohm. So i assume the problem is elsewhere.
I also tried to reset the PID without success. The car can start when the G28 is unplugged and it runs perfectly when it is connected but it still has intermittent misfire issues check here at higher RPM. The coolant sensor (G62), even when it is unplugged, shows an ice temperature of -49c. Also, i noticed that the gauge for oil pressure in the cockpit is showing 2 bar while the actual pressure is 0.0 when I crank up the engine.
I don't know what to do. I think I've all other possibilities out. I'm concerned that i may have missed something. If anyone has any ideas please let me know! TIA!
3. Fuel Pump
The fuel pump on the g28 is activated by a signal from the RPM sensor. The GM-style sensor is identical to the G4 and both function in the 80, 100 200, UrS and RS2 cars so you can easily find one at a junkyard or website from a parts store. It is simple to test them - just put your DMM into resistance mode and measure the distance between pins 1 and 2 (with the bump at the connector's end facing up). They must be infinite Ohms.
4. ECU
Our 20vt turbo (3B, AAN, ABY and ADU) engines are equipped with an ECU that has to know the speed and position of the crankshaft to make decisions regarding timing of the fuel injector, for example. To accomplish this, it makes use of a Crank Position Sensor (G4) and an Engine Speed Sensor (G28). If either of these goes bad you will get codes on the diagnostic scanner that could cause engine shut down.
A malfunctioning G28 sensor can cause an inaccurate gearbox speed counter or a gearbox that shifts faster than normal, or a misfire in gear. It is probable that the sensor is failing and needs to be replaced if you notice any of these symptoms. They're inexpensive and easy to locate especially when they're a Bosch sensor like ours. Alternatively, GM's version of this part would be a good option.
5. Tachometer
A malfunctioning engine sensor can cause a myriad of issues in your vehicle. It's a vital component of the Audi's transmission as website it sends information to the ECU about how fast or slow the car's crankshaft is turning. This sensor could cause the transmission to fail and other car components to be affected.
The G5 engine speed sensor is located on the edge of the transmission just above the flywheel ring gear. It sends a signal directly to the ECU at pin T55/49 via a grey wire. The ECU is then able to process this signal to control the flow of fuel, timig and boost, and also sends it on to the G5 Tachometer located in the instrument cluster. You can check the sensor for failure by examining the continuity between it and the tachometer, between ECU pin T55/49 and the instrument cluster connection on pin T6a/1 (trace [79]) as well as between T6a/1, and the instrument cluster pin audi car keys replacement T26a/12. You should get more info observe approximately 1000 ohms of resistance between these two points. This is the same across the Audi 80-100-200-RS2 series, starting from the 1985 MC up to the 1997 UrS AN and the 1995 RS2 DU So, you may find them in wrecking yards.