How to Replace an Audi G28 Engine Speed Sensor
Charles the Humble Technician teaches you how to replace the G28 Engine Speed Sensor. The sensor is situated near the edges of the transmission, above the flywheel ring gear. It transmits a signal to the ECU via an uncolored wire (T55/49), then to the tachometer located in the instrument cluster.
1. Engine Speed Sensor
It is located on the outside of the transmission, above the flywheel ring gear G28 Engine Speed Sensor sends an electrical signal to ECU pin T55/49 using the grey wire. The ECU then uses this information to control the flow of fuel, timig and boost. It also sends an indication to the G5 Tachometer located in the instrument cluster.
The sensor is used to correlate the G40 Camshaft position Sensor. Recommended Website to know when the crankshaft reached TDC and also where the camshaft lies to trigger the spark and injectors.
If this sensor fails, the ECU will throw a P00160 code which means the Crank Shaft and Intake Camshaft are not in sync and possibly indicating the chain stretching or a jump link on the upper chain of timing. However the code will not appear on its own, without additional information from other sensors (G4 and G40).
Testing is a bit challenging because there are two connector pins and they perform different functions but the best way to test it is to measure the resistance between the sensor and the ECU. When the sensor is fully operational, it should read about 1000 ohms. If you're experiencing issues with this sensor, look for signs of oil or coolant in the connector bay.
2. Injectors
Yesterday, while accelerating from 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 weren't firing. Today, i pulled out the spark plugs, three were soaked with gazoline and the 4th one was dry. When i crank the engine without sparks i put tissue on the top of each of the injector holes, the 3 drenched with gazoline pop out, but the 4th stay closed. I checked the ground connection on ECU pins 14/55/30/55/48/55/14/55/48/ I got 0ohm. I assume that the problem is somewhere else.
I also tried to reset the PID but with no luck. The car will start when the G28 is disconnected, but it works fine when the G28 connected. However, the intermittent misfire problem persists at higher RPM. The temperature sensor for coolant (G62) shows the wrong temp value -49c, even if I unplug it. I also noticed that the gauge for oil pressure in the cockpit is showing 2 bar while the actual pressure is 0.0 when i rev the engine.
I'm not sure what to do, as i feel i have pretty much eliminated everything else. 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 receives signals from the RPM sensor. The GM-style transmitter is the same as 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 junkyard or in a local parts store. It is simple to test them - put your DMM in resistance mode and measure between pins 1 (with the bump on the connector's side up) and 2 (2nd from left on the black connector's side). They must be infinite Ohms.
4. ECU
The ECU in our 20vt turbo (3B AAN ABY) engines must be aware of the speed and position of the crankshaft in order to make a decision about timing of the fuel injector, etc. 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 of these sensors, the diagnostic scanner will show the codes that could trigger an engine shut down.
A failing G28 sensor could cause an inaccurate gearbox speed counter and a gearbox which shifts faster than normal, and/or an unfire when in gear. If you are experiencing any of these problems, it is most likely that your sensor is failing and requires replacement. They're cheap and easy to find, especially in the case of a Bosch model like ours. If you prefer, GM's version of this part is a good option.
5. Tachometer
A malfunctioning engine sensor can cause a myriad of issues in your vehicle. It is a crucial part of your Audi's transmission, since it relays information to the ECU about how fast or slow the car's crankshaft is rotating. If this sensor fails, it could cause problems for the transmission and the rest of the car's components.
The G5 engine sensor is located near the edge of the transmission, over the flywheel ring. It sends a signal via gray wire to ECU pin T55/49. The ECU uses this signal to control the amount of fuel and boost, as well as timig. It also sends it to the G5 Tachometer inside the instrument cluster. You can determine if the sensor is in failure by examining the continuity of the sensor to the tachometer. You can also 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 as well as pin T26a/12. It should show around 1000 ohms of resistance between those points. This part is common across the Audi 80-100-200-RS2 model, ranging 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.