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How to Replace an Audi G28 Engine Speed Sensor
Charles the Humble Technician teaches you how to replace the G28 Engine Speed Sensor. This sensor is located near the edges of the transmission above the flywheel ring gear. It transmits a signal to the ECU through an uncolored wire T55/49, then to the tachometer located on the instrument cluster.
1. Engine Speed Sensor
The grey wire is located at the edges of the transmission, above the flywheel ring. The sensor transmits a signal via the grey wire to pin T55/49. The ECU utilizes this information to regulate boost and fuel. It also sends an indicator to the G5 Tachometer in instrument cluster.
The sensor serves as a reference to correlate with the G40 Camshaft Position Sensor. The ecu must know when the crankshaft is TDC and where the camshaft is so it can start spark and injectors in the right way.
If this sensor fails, the ECU will display a P00160 error code. This means that the Crank Shaft is not in line with the Intake Camshaft. It could also be a sign of an issue with the chain or a jumped chain link in the upper chain of timing. However, the code won't be displayed on its own without additional information from other sensors (G4 and G40).
It is a little tricky to test because there are various connector pins, and each has its own functions. The best way to do it is to measure the resistance between the ECU and the sensor. If the sensor is operational, it should read approximately 1000 ohms. Check for evidence of coolant or oil in the connector bay if you have problems with this part.
2. Injectors
Yesterday, as i was accelerating off the highway paytoll at a high speed, i noticed a huge reduction in power. It was like the engine had run out of gas. Or my injectors weren't firing. Today, i pulled out the spark plugs. Three were soaked with gazoline and the 4th one was dry. I put tissue over each injector hole, and when I start the engine with no sparks, the ones with gazoline jump right out. The fourth one remains shut. I checked the ground connection of ECU pins 14,30 and 48/55. I got 0ohm. I assume that the problem is elsewhere.
I also tried to reset PID but without success. The car will start when the G28 is disconnected and it runs perfectly when it is plugged in, but still has intermittent misfire issues at higher RPM. The coolant temperature sensor (G62) shows the wrong temperature of -49c, even if I unplug it. Also, i noticed that the gauge for oil pressure in the cockpit shows 2 bar when the actual pressure is 0.0 when I crank up the engine.
I'm not sure what to do, as i think i've pretty much eliminated everything else. I'm worried that i might have missed something. If anyone has any ideas please chime in! TIA!
3. Fuel Pump
The fuel pump in the g28 receives signals from the RPM sensor. The GM-style transmitter 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 wrecking yard or at a parts store. Testing them is easy by putting your DMM in resistance mode and measure 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 needs to be aware of the speed and position of the crankshaft in order to make decisions regarding timing of the fuel injector, for example. It makes use of a Crank Position Sensor G4 and an Engine Speed Sensor G28 to achieve this. If you have a problem with either one of these, the diagnostic scanner will display codes that could cause an engine shutdown.
A failing G28 sensor could cause an inaccurate speed counter for the gearbox and a gearbox which shifts more quickly than normal, or a misfire while in gear. If you have any of these issues, it is most likely that your sensor is going bad and needs replacing. The good thing is that they are very affordable and readily available particularly in the case of an Bosch model, which is what ours are. Alternatively, the GM version of this part is also a great option.
5. Tachometer
A damaged engine sensor could cause a number of problems in your car. It's an essential component of your Audi's transmission, since it relays information to the ECU about how fast or slow the car's crankshaft is spinning. This sensor could cause the transmission to malfunction and other components in the car to be affected.
The G5 engine speed sensor is located at the outside of the transmission above the flywheel ring gear. It sends 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 relays it to the G5 Tachometer located in the instrument cluster. You can check for sensor failure by checking continuity from the sensor to the tachometer. Additionally, you can check continuity between pin T55/49 of the ECU and pin T6a/1 of the instrument cluster (trace [79trace [79]) and between pin T6a/1 and pin T26a/12. thekeylab.co.uk should observe around 1000 ohms of resistance between those points. This is a common part across the Audi 80, 100, 200, UrS and RS2 range from 1985 MC until the 1997 UrS AAN and 1995 RS2 ADU, so the best ones could be available in wrecking yards.