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. This sensor is situated near the transmission's edge just above the flywheel gear. It sends a signal to the ECU via the grey wire (T55/49) and then to the tachometer within the instrument cluster.
1. Engine Speed Sensor
Located on the edge of the transmission just above the flywheel ring gear, the G28 Engine Speed Sensor sends a signal to ECU pin T55/49 using an uncolored wire. The ECU utilizes this information to control fuel and boost. It also sends signals to the G5 tachometer in the instrument cluster.
The sensor is used to link the G40 Camshaft position Sensor. The ecu has to know when the crankshaft reached TDC, and where the camshaft lies in order to activate the spark and injectors.
If this sensor fails, the ECU will show the P00160 error, 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 code won't be displayed on its own without additional information from other sensors (G4 and G40).
Testing is a bit challenging because there are two pins for the connector and they perform different functions however the best method of testing it is by measuring resistance between the sensor and the ECU. If the sensor is operational, it should read approximately 1000 ohms. If you are having problems 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 drop in power. It was as if the engine had run out of gas. Or my injectors weren't firing. In the morning, i removed the spark plugs. Three were soaked with gazoline and the fourth one was dry. I put a piece of tissue over each injector hole and when I start the engine without sparks, the ones with gazoline jump out. The fourth one remains shut. I tested the ground connection of ECU pins 14,30, and 48/55. I found 0ohm. I assume that the problem is in another location.
I also tried to reset the PID with no success. This Web page will start when the G28 is unplugged, and it works fine when the G28 plugged in. However the intermittent misfire issue still occurs at higher RPM. The coolant sensor (G62) even if it is not plugged in, shows temperatures 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 if i crank up the engine.
I don't know what to do. I believe that I've ruled everything else out. I'm afraid i may have missed something. Please let me know If you have any suggestions! TIA!
3. Fuel Pump
The fuel pump on the g28 is activated by a signal sent by the RPM sensor. The GM-style transmitter is identical to 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 from a parts store. Test them out by putting your DMM in resistance mode and measure the resistance between pins 1 (with the bump on the connector's side up) and 2 (2nd from 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 be aware of the speed and position of the crankshaft to make decisions about 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 advanced key audi are experiencing issues with either of these, the diagnostic scanner will show codes that could cause the engine shutting down.
A malfunctioning G28 sensor can cause an inaccurate gearbox speed counter or a gearbox that shifts faster than normal, and/or a misfire in the gear. If you have any of these issues, it is most likely that your sensor is deteriorating and needs replacing. The good news is they are quite affordable and readily available, especially in the case of the Bosch unit which is what ours are. You can also choose the GM version of this unit is also a good option.
5. Tachometer
A malfunctioning engine speed sensor could be the reason behind a slew of issues in your vehicle. It's an essential component of the transmission in your Audi since it sends information to the ECU on how fast or slowly the engine of the car is turning. If this sensor fails, it will affect 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 an electrical signal through an uncolored wire to the ECU pin T55/49. The ECU uses this signal to regulate the flow of fuel and boost and also to timigrate. It also sends it to the G5 Tachometer located in the instrument cluster. You can test the sensor for failure by checking 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 [79trace [79]) and between pin T6a/1 and the instrument cluster pin T26a/12. You should see the resistance to be around 1000 ohms between these two points. This is a common feature across the Audi 80-100-200-RS2 series, starting 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.