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How to Replace an Audi G28 Engine Speed Sensor

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

1. Engine Speed Sensor

The sensor is located at the edge of the transmission, above the flywheel ring gear, the G28 Engine Speed Sensor sends an electrical signal to ECU pin T55/49 via a grey wire. The ECU uses this information to regulate the amount of fuel and boost. It also sends an indicator to the G5 Tachometer located in the instrument cluster.

The sensor is used to link the G40 Camshaft position Sensor. The ecu needs to know when the crankshaft is TDC and where the camshaft is located so that it can trigger spark and injectors according to the situation.

If this sensor fails, the ECU will show an error code P00160 which indicates that the Crank Shaft and Intake Camshaft are out of sync, possibly indicating the chain stretching or a jump link on the upper timing chain. However the code will not be displayed on its own without additional information from other sensors (G4 and G40).

It's a bit tricky to test since 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. It should read about 1000 ohms if the sensor is in full operation. If you're experiencing issues with this component, look for evidence of coolant or oil in the connector bay.

2. Injectors

Yesterday, as i was accelerating off the highway paytoll at maximum speed I noticed a massive drop in power. It was like the engine had run out of gas. Or, my injectors weren't firing. Today, i pulled out the spark plugs, three were soaked with gazoline and the fourth one was dry. When i crank the engine without sparks, i place a tissue on the top of each hole in the injector, the 3 drenched with gazoline leap out, however the 4th stay shut. I tried to test the ground connections of ECU pins 14,30, and 48/55. I found zero ohm. I'm assuming that the issue is somewhere else.

I also tried to reset the PID without success. The car will start if the G28 is disconnected and is running fine when it is plugged in, but still is experiencing intermittent misfires 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 bars when the actual pressure is zero.





I don't know what to do. I feel like i've pretty much eliminated everything else. I'm concerned that i may have missed something. If anyone has any ideas please share them! TIA!

3. Fuel Pump

The fuel pump of the g28 receives signals from the RPM sensor. The GM-style transmitter is the same as the G4 and both are used in the 80 100, 200, UrS and RS2 cars so you can easily find one at a salvage yard or at a parts store. It is easy to test them - just put your DMM into resistance mode and measure the distance between pins 1 and 2 (with the bump at the connector end facing upwards). audi lost key G28 must be infinite Ohms.

4. ECU

The ECU of our 20vt turbo (3B AAN ABY ADU) engines must be aware of the position and speed of the crankshaft to make decisions regarding 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 either of these goes wrong, you will receive codes on the diagnostic scanner which can lead to engine shutdown.

A failing G28 sensor could result in an inaccurate speed counter for the gearbox or a gearbox that shifts more quickly 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 quite affordable and readily available particularly when you're looking at a Bosch unit like ours. Alternately, GM's version this part would be a good option.

5. Tachometer

A damaged engine sensor could cause a variety of issues in your car. It's a crucial component of the transmission of your Audi, as it transmits information to the ECU regarding how fast or slowly the car's engine is spinning. If the sensor fails, it could cause problems for the transmission, as well as the other car's components.

The G5 engine speed sensor is located on the outside of the transmission just above the flywheel ring gear and transmits a signal to the ECU at pin T55/49 through an uncolored wire. The ECU uses this signal to control fuel and boost, as well as timig. It also sends it to the G5 Tachometer inside 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 on pin T6a/1 (trace [79trace [79]) and between T6a/1 and the instrument cluster pin T26a/12. There should be an average resistance of 1000 ohms in these areas. This is the same across the Audi 80-100-200-RS2 range, beginning with the 1985 MC and up to the 1997 UrS An and 1995 RS2 DU So, you may find some good ones in wrecking yards.