How to Replace an audi a3 key fob G28 Engine Speed Sensor

In this video Charles the Humble Mechanic shows how to replace the G28 engine speed sensor. This sensor is situated at the edge of transmission, above the flywheel gear. It transmits a signal to the ECU through a grey wire T55/49, then to the tachometer on the instrument cluster.

1. Engine Speed Sensor

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

The sensor is used as a reference for comparing with the G40 Camshaft Position Sensor. The ecu needs to know when the crankshaft is TDC and where the camshaft is so it can trigger spark and injectors accordingly.

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

It can be a bit difficult to test as there are different pins on the connector and each has its own functions. The best method for doing this is by measuring the resistance between the ECU and the sensor. It should read approximately 1000 ohms if the sensor is at full operation. Check for signs of coolant or oil in the connector bay if there are issues with this component.

2. Injectors

Yesterday, as i was accelerating off the highway paytoll at full speed, i noticed a huge decrease in power. It was like the engine had run out of gas. Or my injectors were not firing. Today, i pulled out the spark plugs, 3 were drenched in gazoline, the fourth one was dry. I put a piece of tissue over each injector hole, and when I start the engine with no sparks, the three with gazoline jump out. The 4th one stays closed. I tested the ground connection of ECU pins 14,30 and 48/55. I got 0ohm. I think the issue is somewhere else.

I also tried to reset the PID with no success. The car will start when the G28 is disconnected, but it works fine when the G28 connected. However the intermittent misfire issue persists at higher RPM. The coolant temperature sensor (G62) shows the wrong temperature value of -49c even when i unplug it. I also noticed that the oil gauge in the cockpit shows 2 bars when the actual pressure is 0.

I don't know what to do. I believe that I've eliminated everything else. I'm afraid i may have missed something. If anyone has suggestions, please share them! TIA!

3. Fuel Pump

The fuel pump in the g28 can be activated by a signal from the RPM sensor. The GM-style transmitter functions similarly to the G4 sender and works on the 80,100,200, UrS, and RS2 vehicles. You can easily locate the spare in a salvage shop or parts store. It is easy to test them: simply put your DMM into resistance mode and determine the distance between pins 1 and 2 (with the bump at the connector end facing upwards). They must be infinite Ohms.

4. ECU

The ECU in our 20vt turbo (3B AAN ABY) engines requires to be aware of the speed and position of the crankshaft to determine timing of the fuel injector, etc. It makes use of a Crank Position Sensor G4 and an Engine Speed Sensor G28 to accomplish this. If you have a problem with either of these sensors, the diagnostic scanner will display codes that could cause the engine shutting down.

Some of the symptoms of a malfunctioning G28 sensor are an inaccurate gearbox rev counter, gears shifting quicker than normal, and/or a misfire when you're in gear. It is probable that your sensor is failing and requires to be replaced if you notice any of these signs. They're inexpensive and easy to locate particularly when they're an Bosch sensor like ours. If you prefer, GM's version of this part is an excellent choice.

5. Tachometer

A malfunctioning engine sensor can cause a variety of issues within your vehicle. It's a crucial component of the transmission of your audi keyless go, as it transmits information to the ECU about how fast or slow the engine is turning. When this sensor repairer fails, it can affect the performance of the transmission as well as the rest of the car's components.

The G5 engine sensor is located at the edge of transmission, above the flywheel ring. It transmits signals via gray wire to ECU pin T55/49. The ECU utilizes this signal to regulate fuel and boost, and also timig. It also sends it to the G5 Tachometer inside the instrument cluster. You can check for sensor failure by examining the 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 and pin T26a/12. You should see the resistance to be around 1000 ohms in these areas. This is a common feature across the replacement audi a4 key 80-100-200-RS2 series, starting from the 1985 MC all the way up to the 1997 UrS AN and 1995 RS2 DU So, you may find them in wrecking yards.