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 near the transmission's edge just above the flywheel gear. It transmits a signal the ECU via a grey wire (T55/49) and then to the tachometer in the instrument cluster.

1. Engine Speed Sensor

The grey wire is situated on the edge of transmission, just above the flywheel ring. The sensor sends an electrical signal through the grey wire to pin T55/49. The ECU then uses this information to control the flow of fuel, timig and boost. It also sends an alert to the G5 Tachometer in instrument cluster.

The sensor is used to connect 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 in the right way.

If this sensor fails, the ECU will display an error code P00160 which indicates that the Crank Shaft and Intake Camshaft aren't in sync and possibly indicating the chain is stretched or a jump link on the upper timing chain. The code won't appear without the additional information supplied by other sensors (G4 or G40).

Testing is a bit tricky since there are two connector pins, and they serve different purposes however the best method to test it is to measure the resistance between the sensor and the ECU. When the sensor is operational, it should be reading about 1000 ohms. Check for evidence of coolant or oil in the connector bay if you have problems with this part.


2. Injectors

Yesterday, when i was accelerating to the fullest speed from highway paytoll i had a big cut in power like the engine is running out of gas or the injectors are not firing any more. This morning i pull out the spark plugs, three 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 ones with gazoline jump right out. 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 with no success. The car will start when the G28 is disconnected, but it runs fine with the G28 connected. However the intermittent misfire issue continues to occur at higher RPM. The coolant sensor (G62), even when unplugged, still shows a temperature of -49c. Also i noticed that the oil pressure gauge in the cockpit is showing 2 bar, whereas the actual pressure is 0.0 if i crank up the engine.

I'm not sure what to do, i think i've pretty much completely ruled out all other possibilities. I'm worried that i might have missed something. If anyone has any suggestions, please chime in! TIA!

3. Fuel Pump

The fuel pump in the g28 is activated by a signal from the RPM sensor. they said -style transmitter is similar to the G4 sender, and both operate on the 80,100,200, UrS, and RS2 vehicles. You can easily locate a spare in a wrecking shop or parts store. It is easy to test them - simply put your DMM into resistance mode and measure the distance between pins 1 and 2 (with the bump at the connector end facing upwards). They should be infinite ohms.

4. ECU

The ECU in our 20vt turbo (3B AAN ABY ADU) engines requires to know the speed and position of the crankshaft in order to make a decision about timing of fuel injectors, 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, the diagnostic scanner will show codes that could cause the engine shutting down.

A damaged G28 sensor could result in an inaccurate gearbox speed counter and a gearbox which shifts more quickly than normal, or a misfire while in the gear. It is possible that your sensor is failing and requires to be replaced if you experience any of these symptoms. The good news is that they are very affordable and easy to find particularly in the case of an Bosch unit like ours. Alternatively, the GM version of this component is also a good choice.

5. Tachometer

A malfunctioning engine sensor can cause a number of problems in your vehicle. It's a vital component of your Audi's transmission, since it relays information to the ECU about how fast or slow the car's crankshaft is turning. If this sensor fails, it could affect the performance of the transmission and the rest of the car's components.

The G5 engine speed sensor is located at the edge of the transmission, above the flywheel ring gear and sends a signal directly to the ECU at pin T55/49 through a grey wire. The ECU utilizes this signal to control fuel and boost, and also timig. It also transmits it to the G5 Tachometer located in the instrument cluster. You can check the sensor for failure by examining the continuity between it and the tachometer, between the ECU pin T55/49 and the instrument cluster connection to pin T6a/1 (trace [79trace [79]) as well as between T6a/1, and the instrument cluster pin T26a/12. You should detect the resistance to be around 1000 ohms between these points. This is a common feature across the Audi 80-100-200-RS2 range, from the 1985 MC all the way up to the 1997 UrS An and 1995 RS2 Du, so you might find good ones in wrecking yards.