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How to Replace an audi a3 keys 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 just above the flywheel ring gear. It transmits a signal to the ECU via a grey wire (T55/49) which is then sent to the tachometer within 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 signals to ECU pin T55/49 via the grey wire. The ECU utilizes this information to regulate boost and fuel. It also sends an indicator to the G5 Tachometer located in the instrument cluster.

The sensor serves as a reference point to connect with the G40 Camshaft Position Sensor. The ecu needs to be aware of when the crankshaft has reached TDC and also where the camshaft lies to trigger the spark and injectors.

If this sensor fails the ECU will display the P00160 error, which means the Crank Shaft and Intake Camshaft are not in sync and possibly indicating chain stretch or a jumped link on the upper timing chain. The code won't show without the additional information supplied by other sensors (G4 or G40).

It can be a bit difficult to test since there are different pins on the connector, and they all have different functions. The best way to do it is to measure the resistance between the ECU and the sensor. It should read approximately 1000 ohms when the sensor is in full operation. Look for signs of coolant or oil in the connector bay if there are problems with this part.

2. Injectors

Yesterday accelerating full speed from highway paytoll, i experienced a big cut in power like the engine is out of gas or injectors are not firing at all. This morning i pull out the spark plugs, three were drenched with gazoline the fourth one was dry. When i crank the engine without sparks, i place a tissue on top of each injector hole and the 3 that were drenched in gazoline jump out but the 4th stays closed. I inspected the ground connection on ECU pins 14/55,30/55 and 48/55 I get 0ohm. So i assume the problem is somewhere else.

I also tried to reset the PID but without success. The car is able to start if the G28 is disconnected and runs fine when it is plugged in however it has intermittent misfire issues 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 bars but the actual pressure is zero.

I'm not sure what to do. I think I've all other possibilities out. But i'm worried that I may have missed something. If anyone has any ideas please chime in! TIA!

3. Fuel Pump

The fuel pump in the g28 can be activated by a signal by 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 so you can easily find one at a salvage yard or at a parts store. It is easy to test them - just put your DMM into resistance mode and determine the distance between pins 1 and 2 (with the bump at the connector's end facing up). They should be infinite ohms.

4. ECU

The ECU in our 20vt turbo (3B AAN ABY) engines requires to be aware of the position and speed of the crankshaft to make decisions regarding timing of the fuel injector, Audi A3 Replacement Key etc. In order to do this it utilizes a Crank Position Sensor (G4) and an Engine Speed Sensor (G28). If either of these goes badly, you will see codes on the diagnostic scanner which can cause the engine to shut down.

A damaged G28 sensor can cause an inaccurate speed counter for your gearbox or a gearbox that shifts faster than normal, or a misfire while in gear. If you are experiencing any of these issues, it is likely that your sensor is failing and should be replaced. They're cheap and easy to find especially when they're a Bosch model like ours. Alternately, the GM version of this component is also a great option.

5. Tachometer

A faulty engine speed sensor could be the cause of a slew of issues in your car. It's a vital component of the audi key's transmission because it communicates to the ECU about how fast or slow the car's crankshaft is turning. If the sensor fails, it will disrupt the performance of the transmission and the other car's components.

The G5 engine sensor is located near the edge of transmission, above the flywheel ring. It transmits a signal via a gray wire to the ECU pin T55/49. The ECU utilizes this signal to regulate the amount of fuel and boost, as well as timig. It also relays it to the G5 Tachometer in instrument cluster. You can check for sensor failure by checking continuity from 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. You should observe approximately 1000 ohms of resistance between those two pins. This is a common feature across the audi replacement keys 80-100-200-RS2 series, starting beginning with the 1985 MC and up to the 1997 UrS AN and 1995 RS2 Du, so you might find them in wrecking yards.