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How to Replace an Audi G28 Engine Speed Sensor

In this video, Charles the Humble Mechanic demonstrates how to replace audi key fob the G28 engine speed sensor. This sensor is situated at the edge of transmission over the flywheel gear. It transmits a signal the ECU via the grey wire (T55/49) which is then sent to the tachometer within the instrument cluster.

1. Engine Speed Sensor

The sensor is located at the edge of the transmission above the flywheel ring gear G28 Engine Speed Sensor sends signals to ECU pin T55/49 via an uncolored wire. The ECU uses this information to control fuel and boost. It also sends an alert to the G5 Tachometer within the instrument cluster.

The sensor is used to link with the G40 Camshaft position Sensor. The ecu needs to be aware of when the crankshaft has reached TDC, and the location of the camshaft to trigger the spark and injectors.

If this sensor fails, the ECU will show a P00160 code which means the Crank Shaft and Intake Camshaft aren't in sync, 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).

Testing can be a bit difficult since there are two connector pins, and they have different functions however the best method of testing it is to measure resistance between the sensor and the ECU. It should read approximately 1000 ohms when it is in full operation. If you are having problems with this sensor, look for audi Spare keys evidence of oil or coolant in the connector bay.

2. Injectors

Yesterday, while accelerating from the highway paytoll at a high speed, i noticed a huge decrease in power. It was as if the engine was running out of gas. Or, my injectors weren't firing. In the morning, i removed the spark plugs, 3 were drenched with gazoline the fourth one was dry. When I crank the engine, there are no sparks, i place a tissue on top of each injector hole, the 3 drenched with gazoline jump out but the 4th stays closed. I checked the ground connection of ECU pins 14,30, and 48/55. I got 0ohm. So i assume the problem is in another place.

I also tried to reset the PID but with no luck. The car will start when the G28 is not plugged in and it runs perfectly when it is plugged in but it still has the intermittent misfire issue at higher RPM. The temperature sensor for the coolant (G62) shows the wrong temp value -49c even when i unplug it. I also noticed that the oil pressure gauge in the cockpit is showing 2 bar, whereas the actual pressure is 0.0 when I crank up the engine.

I don't know what to do. I think I've eliminated everything else. But i'm worried that i might have missed something. If anyone has any suggestions, please let me know! TIA!

3. Fuel Pump

The fuel pump in the g28 receives signals from the RPM sensor. The GM-style transmitter is identical to the G4 sender and works on the 80,100,200, UrS, and RS2 vehicles. You can easily find an extra in a wrecking shop or parts store. Test them out by putting your DMM in resistance mode and measure the resistance between pins 1 (with the bump on the connector's side up) and 2 (2nd from the left on the black end of the connector). They should be infinite ohms.

4. ECU

Our 20vt turbo (3B AAN, ABY and ADU) engines have an ECU that must know the speed and position of the crankshaft to make a decision about timing of the fuel injectors, etc. It makes use of 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 codes that could lead to an engine shut down.

A failing G28 sensor can cause an inaccurate speed counter for the gearbox or a gearbox that shifts faster than normal, and/or an unfire when in gear. It is possible 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 readily available, especially in the case of a Bosch unit which is what ours are. If you prefer, GM's version of this part is a good option.

5. Tachometer

A damaged engine sensor could cause a variety of issues in your car. It's an essential component of the Audi's transmission since it relays information to the ECU about how fast or slow the car's crankshaft is turning. If the sensor fails, it will cause problems for the transmission and the rest of the car's components.

The G5 engine speed sensor is located at the outside 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 is then able to process this signal to regulate fuel, timig and boost as well as transmitting it to the G5 tachometer in the instrument cluster. You can test the sensor for any failure by checking the continuity between it and the tachometer. You can also check continuity between ECU pin T55/49 and the instrument cluster connection to pin T6a/1 (trace [79trace [79]) and between T6a/1 and the instrument cluster pin T26a/12. You should observe approximately 1000 ohms resistance between these two points. This is a typical part that is found across the audi spare keys 80, 100 200, UrS and RS2 range from 1985 MC until the 1997 UrS AAN and 1995 RS2 ADU. Good parts could be found in wrecking yards.