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How to Replace an audi a5 key fob G28 Engine Speed Sensor

In this video, Charles the Humble Mechanic demonstrates how to replace the G28 engine speed sensor. The sensor is located on the edge of the transmission above the flywheel ring gear. It transmits a signal to the ECU via 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 the G28 Engine Speed Sensor sends a signal to ECU pin T55/49 through the grey wire. The ECU uses this information to control boost and fuel. It also sends an alert to the G5 Tachometer located in the instrument cluster.

The sensor is used as a reference for comparing with the G40 Camshaft Position Sensor. The ecu has to know when the crankshaft reached TDC and also the position of the camshaft, to trigger the spark and injectors.

If this sensor fails, the ECU will display an error code P00160. This means that the Crank Shaft is out of alignment with the Intake Camshaft. It could also indicate an issue with the chain or a jump in the chain link of the upper timing chain. However, the error code won't be displayed on its own without additional information from other sensors (G4 and G40).

It's a bit tricky to test because there are several pins on the connector and they all have different functions. The best method for doing this is to measure the resistance between the ECU and the sensor. When the sensor is fully functional, it should read around 1000 ohms. Check for evidence of coolant or oil in the connector bay if there are issues with this part.

2. Injectors

Yesterday, when accelerating from highway paytoll at a high speed I noticed a significant drop in power. It was as if the engine was running out of gas. Or, my injectors weren't firing. This morning i pull out the spark plugs, 3 were drenched with gazoline the fourth one was dry. When I crank the engine without sparks, i place a tissue on the top of each of the injector holes and the 3 drenched with gazoline leap out, however the 4th one stays shut. I checked the ground connection of ECU pins 14,30, and 48/55. I found zero ohm. I'm assuming that the issue is elsewhere.

I also tried to reset the PID but without success. The car will start when the G28 is disconnected, but it works fine when the G28 connected. However, the intermittent misfire problem continues to occur at higher RPM. The coolant sensor (G62) even if it is not plugged in, shows temperatures of -49c. I also noticed that the oil gauge in the cockpit shows 2 bar when the actual pressure is zero.

I'm not sure what to do. I believe that I've ruled everything else out. But i am afraid I might have missed something. If anyone has any suggestions, repaired please let me know! TIA!

3. Fuel Pump

The fuel pump on the g28 is activated by a signal by the RPM sensor. The GM-style transmitter functions similarly to the G4 sender, and both operate on the 80,100,200, UrS, and RS2 vehicles. You can easily locate an extra in a wrecking shop or parts store. It is easy to test them - just switch your DMM into resistance mode and measure the distance between pins 1 and 2 (with the bump at the connector's end facing up). They should be infinite Ohms.

4. ECU

Our 20vt turbo (3B AAN, ABY, and ADU) engines are equipped with an ECU that must be aware of the speed and position of the crankshaft in order to make a decision about timing of the fuel injectors, etc. In order to do this it utilizes a Crank Position Sensor (G4) and an Engine Speed Sensor (G28). If either of these go wrong, you will receive codes on the diagnostic scanner which can lead to engine shutdown.

Some of the symptoms of a failing G28 sensor include an inaccurate rev counter in the gearbox the gears are shifting faster than normal and/or a misfire when in gear. It is possible that the sensor is failing and needs to be replaced if you notice any of these symptoms. They're cheap and easy to find particularly when they're an Bosch unit like ours. Alternately, GM's version this component is a good option.

5. Tachometer

A faulty engine speed sensor could be a cause for a slew of issues with your vehicle. It is a crucial part of your Audi's transmission, since it relays information to the ECU about how fast or slow the vehicle's crankshaft is turning. If this sensor fails, it can affect the performance of the transmission, as well as the other car's components.

The G5 engine sensor is located at the edge of the transmission, over the flywheel ring. It transmits an electrical signal through gray wire to ECU pin T55/49. The ECU utilizes this signal to control the flow of fuel and boost and also timig. It also sends it to the G5 Tachometer in instrument cluster. You can check for sensor failure by examining the continuity of the sensor to the tachometer. Additionally, you can verify 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 see an average resistance of 1000 ohms between these two points. This is a standard component across the audi car key cover 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.