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

Charles the Humble Technician teaches you how to replace the G28 Engine Speed Sensor. The sensor is located on the edge of the transmission, above the flywheel ring gear. It sends a message to the ECU via the grey wire T55/49 and then to the tachometer on 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 through the grey wire. The ECU uses this information to control boost and fuel. It also sends an indication to the G5 Tachometer within the instrument cluster.

The sensor is used 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 trigger spark and injectors in the right way.

If this sensor fails, the ECU will display an error code P00160. This indicates that the Crank Shaft is out of sync with the Intake Camshaft. It could also be a sign of the possibility of a chain stretch or jump in the chain link of the upper chain. The code won't appear without the additional information supplied by other sensors (G4 or G40).

It is a little tricky to test since there are several pins on the connector, and they all have different functions. The most effective method to test it is to measure the resistance between the ECU and the sensor. It should read approximately 1000 ohms if the sensor is at full operation. Look for evidence of coolant or oil in the connector bay if you have issues with this part.

2. Injectors

Yesterday, as i was accelerating off the highway paytoll at full speed, i noticed a huge reduction in power. It was as if the engine had run out of gas. Or my injectors were not firing. This morning i pull out the spark plugs, 3 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 three with gazoline jump out. The 4th one remains shut. I tested the ground connection of ECU pins 14,30 and 48/55. I got 0ohm. I'm assuming that the issue is somewhere else.

I also tried to reset PID but without success. The car will start when the G28 is unplugged, and it is running fine with the G28 plugged in. However the intermittent misfire issue still occurs at higher RPM. The coolant sensor (G62) even when it is unplugged, shows a temperature of -49c. Also, i noticed that the oil pressure gauge in the cockpit shows 2 bar when the actual pressure is 0.0 when i rev the engine.

I'm not sure what to do, i think i've pretty much eliminated everything else. But i'm worried that i might have missed something. If anyone has suggestions, please chime in! TIA!

3. Fuel Pump

The fuel pump on the g28 is activated by a signal sent by the RPM sensor. The GM-style transmitter functions similarly to the G4 sender and both work on the 80,100,200, UrS, and RS2 vehicles. You can easily locate an extra in a wrecking shop or a 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 connector's side). They must be infinite Ohms.

4. ECU

The ECU of our 20vt turbo (3B AAN ABY) engines must be aware of the position and speed the crankshaft to determine fuel injector audi a3 keys timing, etc. It utilizes a Crank Position Sensor G4 and an Engine Speed Sensor G28 to achieve this. If you have a problem with either of these, the diagnostic scanner will show the codes that could trigger an engine shut down.

A failing G28 sensor could result in an inaccurate speed counter for your gearbox, a gearbox that shifts faster than normal, and/or a misfire while in the gear. It is likely that the sensor is failing and needs to be replaced if you experience any of these symptoms. The good news is they are quite affordable and easy to find, especially when you're looking at a Bosch unit which is what ours are. If you prefer, GM's version of this component is an excellent choice.

5. Tachometer

A malfunctioning engine speed sensor could be the reason behind many problems in your vehicle. It is a crucial part of the Audi a3 keys's transmission since it relays information to the ECU about how fast or slow the vehicle's crankshaft is turning. This sensor can cause the transmission to malfunction and other components of the car to be affected.

The G5 engine speed sensor is situated on the edge of the transmission above the flywheel ring gear and sends a signal directly to the ECU at pin T55/49, via a grey wire. The ECU then processes this signal to regulate fuel, timig and boost and then transmitting it to the G5 tachometer inside the instrument cluster. You can test the sensor for failure by checking continuity between it and the tachometer, audi a3 keys between the 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 see approximately 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 through the 1997 UrS AAN and 1995 RS2 ADU so good parts could be found in wrecking yards.