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How to Replace an Audi A3 Spare key G28 Engine Speed Sensor

Charles the Humble Technician teaches how to replace the G28 Engine Speed Sensor. This sensor is situated on the outside of the transmission over the flywheel gear. It transmits a signal to the ECU through a grey wire T55/49, then to the tachometer located on the instrument cluster.

1. Engine Speed Sensor

Located on the edge of the transmission, above the flywheel ring gear the G28 Engine Speed Sensor sends a signal to ECU pin T55/49 using the grey wire. The ECU utilizes this information to regulate boost and fuel. It also sends signals to the G5 tachometer inside the instrument cluster.

The sensor serves as a reference to correlate with the G40 Camshaft Position Sensor. The ecu has to be aware of when the crankshaft has reached TDC, and the position of the camshaft, in order to activate the spark and injectors.

If this sensor fails to function, the ECU will display a P00160 error message. This means that the Crank Shaft is out of line with the Intake Camshaft. It could also indicate a chain stretch or a jump in the chain link of the upper timing chain. The code won't show without the additional information supplied by other sensors (G4 or G40).

Testing is a bit challenging since there are two pins for the connector and they serve different purposes however the best way to test it is to measure the resistance between the sensor and audi A3 Spare key the ECU. If the sensor is functional, it should read approximately 1000 ohms. Look for signs of coolant, or oil in the connector bay if you are experiencing problems with this part.

2. Injectors

Yesterday, when accelerating from highway paytoll at full speed I noticed a massive drop in power. It was like the engine had run out of gas. Or my injectors were not firing. I pulled out the spark plugs this morning and found that 3 were soaked with gasoline and the fourth was dry. When I crank the engine without sparks i put tissue on the top of each hole in the injector and the 3 that were drenched in gazoline pop out, but the 4th one stays closed. I checked the ground connection of ECU pins 14,30, and 48/55. I got 0ohm. So i assume the problem is somewhere else.

I also tried to reset PID without success. The car will start when the G28 is unplugged, and it runs fine with the G28 connected. However, the intermittent misfire problem continues to occur at higher RPM. The coolant temperature sensor (G62) shows the wrong temperature of -49c, even if I unplug it. I also noticed that the oil gauge in the cockpit shows 2 bar but the actual pressure is zero.

I'm not sure what to do, i think i've pretty much completely ruled out all other possibilities. But i am afraid i might have missed something. 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 sender is identical to the G4 and they both work 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. Test them out by putting your DMM in resistance mode and take measurements 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 must be infinite ohms.

4. ECU

Our 20vt turbo (3B, AAN, ABY and ADU) engines have an ECU that must know the position and speed of the crankshaft in order to make a decision about timing of the fuel injector, for example. In order to do this it makes use of a Crank Position Sensor (G4) and an Engine Speed Sensor (G28). If either of these go badly, you will see codes on the diagnostic scanner which can cause the engine to shut down.

A failing G28 sensor could cause an inaccurate speed counter for the gearbox or a gearbox that shifts more quickly than normal, or a misfire in the gear. If you experience any of these issues, it is likely your sensor is going bad and requires replacement. They are cheap and easy-to-find, especially if they're a Bosch unit like ours. Alternatively, GM's version of this part would be an excellent choice.

5. Tachometer

A malfunctioning engine speed sensor could be the cause of many issues in your vehicle. It's an essential component of the transmission of your Audi because it relays information to the ECU regarding how fast or slowly the engine of the car is turning. If this sensor fails, it could disrupt the performance of the transmission, as well as the other car's components.

The G5 engine speed sensor is located on the edge of the transmission, above the flywheel ring gear and sends a signal to the ECU at pin T55/49 via an uncolored wire. The ECU then processes this signal to regulate fuel, timig, and boost and then transmitting it to the G5 tachometer in the instrument cluster. You can test the sensor for failure by checking continuity between it and the tachometer, between the ECU pin T55/49 and the instrument cluster connection on pin T6a/1 (trace [79]) and between pin T6a/1 and the instrument cluster pin T26a/12. You should see an average resistance of 1000 ohms in these areas. This is a common part that is found across the audi key programming 80, 100, 200, UrS and RS2 range from 1985 MC to the 1997 UrS AAN and 1995 RS2 ADU. Good ones could be available in wrecking yards.