How to Replace an audi a1 key fob G28 Engine Speed Sensor

In this video Charles the Humble Mechanic shows how to replace the G28 engine speed sensor. The sensor is located at the edge of transmission, above the flywheel gear. It transmits a signal the ECU via a grey wire (T55/49) which is then sent to the tachometer in the instrument cluster.

1. Engine Speed Sensor

It is located on the outside of the transmission, above the flywheel ring gear, the G28 Engine Speed Sensor sends signals to ECU pin T55/49 using an uncolored wire. The ECU then uses this information to control the boost, fuel, and timig. It also sends an indicator to the G5 Tachometer within the instrument cluster.

The sensor serves as a reference for comparing with the G40 Camshaft Position Sensor. The ecu must be aware when the crankshaft is TDC and the location of the camshaft so it can start spark and injectors accordingly.

If this sensor fails, the ECU will display an error code P00160 which indicates that the Crank Shaft and Intake Camshaft aren't in sync, possibly indicating chain stretch or a jumped link on the upper timing chain. However the code will not appear on its own, without additional information from other sensors (G4 and G40).

It can be a bit difficult to test as there are various pins on the connector, and each has its own functions. The best way to do it is to measure the resistance between the ECU and the sensor. When the sensor is operational, it should read about 1000 ohms. Look for evidence of coolant or oil in the connector bay if there are issues with this component.

2. Injectors

Yesterday, while accelerating at full speed from the highway paytoll i had an abrupt drop in power like the engine is out of gas or injectors aren't firing any more. I took out the spark plugs this morning, three were soaked with gasoline and the fourth was dry. When i crank the engine with no sparks, i place a tissue on top of each injector hole, the 3 drenched with gazoline jump out but the 4th one stays closed. I tested the ground connection of ECU pins 14,30 and 48/55. I got zero ohm. Therefore, i think the issue is somewhere else.

I also tried to reset the PID without success. The car is able to start when the G28 is disconnected and runs fine when it is connected, but still has the intermittent misfire issue at higher RPM. The coolant sensor (G62), even if it is not plugged in, shows an ice temperature of -49c. I also noticed that the oil gauge in the cockpit shows 2 bars while the actual pressure is zero.

I'm not certain what to do, as i believe that i've completely ruled out all other possibilities. However, i'm afraid that I may have missed something. If anyone has any ideas please share them! TIA!

3. Fuel Pump

The fuel pump of the g28 gets a signal from the RPM sensor. The GM-style sensor is identical to 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 in a local parts store. It is simple to test them to do - just put your DMM in resistance mode and measure between pins 1 (with the bump on the connector end up) and 2 (2nd from left on the black end of the connector). They should be infinite ohms.

4. ECU

The ECU of our 20vt turbo (3B AAN ABY ADU) engines must know the speed and position of the crankshaft to determine timing of fuel injectors, etc. To accomplish this, it uses a Crank Position Sensor (G4) and an Engine Speed Sensor (G28). If either of these go bad you will get codes on the diagnostic scanner which can cause the engine to shut down.

A failing G28 sensor could cause an inaccurate speed counter for your gearbox, a gearbox that shifts faster than normal, and/or an unfire when in the gear. It is probable that the sensor is failing and needs to be replaced if you experience any of these signs. The good news is they are very cheap and readily available particularly if you're looking at the Bosch unit like ours. Alternately, the GM version of this part is also a good option.

5. Tachometer

A damaged engine sensor could cause a myriad of issues in your vehicle. It's a vital component of the audi new key's transmission because it communicates to the ECU about how the car's crankshaft is turning. If this sensor fails, it can cause problems for the transmission as well as the other car's components.

The G5 engine sensor is located at the edge of transmission, above the flywheel ring. It transmits an electrical signal through gray wire to ECU pin T55/49. The ECU uses this signal to control the flow of fuel and boost and also to timigrate. It also sends it to the G5 Tachometer inside the instrument cluster. You can check 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 on pin T6a/1 (trace [79trace [79]) and between pin T6a/1 and the instrument cluster pin T26a/12. You should detect an average resistance of 1000 ohms between these points. This is the same across the Audi 80-100-200-RS2 range, from the 1985 MC all the way up to the 1997 UrS AN and the 1995 RS2 DU So, you may find some good ones in wrecking yards.