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 located near the edges of the transmission, above the flywheel ring gear. It sends a signal to the ECU via a grey wire (T55/49), then to the tachometer within the instrument cluster.
1. Engine Speed Sensor
The sensor is located at the edge of the transmission just above the flywheel ring gear, the G28 Engine Speed Sensor sends an electrical signal to ECU pin T55/49 through the grey wire. The ECU uses this information to control boost and fuel. It also sends a signal to the G5 Tachometer located in the instrument cluster.
The sensor is used as a reference point to connect with the G40 Camshaft Position Sensor. The ecu has to be aware of when the crankshaft has reached TDC, and where the camshaft lies so that it can activate the spark and injectors.
If this sensor fails the ECU will throw a P00160 code which means the Crank Shaft and Intake Camshaft aren't in sync and could indicate the chain stretching or a jump link on the upper timing chain. The code will not appear without the additional information provided by other sensors (G4 or G40).
It is a little tricky to test since there are various pins on the connector, and each one has different functions. The most effective method to test it is to measure the resistance between the ECU and the sensor. If the sensor is operational, it should read around 1000 ohms. Check for signs of coolant or oil in the connector bay if there are issues with this part.
2. Injectors
Yesterday, as i was accelerating off the highway paytoll at full speed I noticed a significant decrease in power. It was as if the engine had run out of gas. Or, my injectors were not firing. I took out the spark plugs this morning, three were soaked in gasoline, and the fourth was dry. When audi car key replacement start the engine with no sparks, I put a piece of tissue on the top of each of the injector holes and the 3 drenched with gazoline leap out, however the 4th one stays shut. I checked the ground connection on ECU pins 14/55, 30/55 and 48/55. i get zero Ohm. I assume that the problem is somewhere else.
I also tried to reset the PID with no success. The car will start when the G28 is unplugged, and it runs fine with the G28 connected. However, the intermittent misfire problem still occurs at higher RPM. The coolant sensor (G62) even when it is unplugged, shows an ice temperature of -49c. Also, i noticed that the oil pressure gauge in the cockpit shows 2 bar when the actual pressure is 0.0 when i rev the engine.
I'm not sure what to do. I think I've eliminated everything else. But i am afraid I may have missed something. If anyone has suggestions, please share them! TIA!
3. Fuel Pump
The fuel pump on the g28 is activated by a signal sent from the RPM sensor. The GM-style sender is the same as the G4 and both function in the 80 100 200, UrS and RS2 cars which is why you can easily locate one at a salvage yard or at a parts store. Testing them is easy to do - just put your DMM in resistance mode and take measurements between pins 1 (with the bump on the connector end up) and 2 (2nd from left on the black end of the connector). They must be infinite Ohms.
4. ECU
The ECU of our 20vt turbo (3B AAN ABY ADU) engines needs to know both the speed and position of the crankshaft in order to make a decision about timing of fuel injectors, etc. To do this, it uses a Crank Position Sensor (G4) and an Engine Speed Sensor (G28). If either of these sensors go bad you will get codes on the diagnostic scanner that can cause the engine to shut down.
The signs of a failing G28 sensor are an inaccurate rev counter in the gearbox and gears that shift faster than normal and/or misfiring when you're in gear. It is possible that the sensor is failing and needs to be replaced if you experience any of these signs. They're inexpensive and easy to locate especially when they're an Bosch sensor like ours. Alternately, the GM version of this unit is also a great option.
5. Tachometer
A failing engine speed sensor could be the reason behind many issues with your car. It's a vital component of the Audi's transmission since it relays information to the ECU about how fast or slow the vehicle's crankshaft is spinning. If the sensor fails, it will affect the performance of the transmission as well as the other car's components.
The G5 engine speed sensor is situated on the edge of the transmission just above the flywheel ring gear and transmits a signal to the ECU at pin T55/49 through a grey wire. The ECU utilizes this signal to control fuel and boost, and also timig. It also sends 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 on pin T6a/1 (trace [79trace [79]) as well as between T6a/1, and the instrument cluster pin T26a/12. You should see approximately 1000 ohms resistance between those two pins. This is the same across the Audi 80-100-200-RS2 series, starting from the 1985 MC up to the 1997 UrS AN and 1995 RS2 DU So, you may find them in wrecking yards.