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 situated at the top of the transmission just above the flywheel ring gear. It transmits a signal to the ECU via a grey wire (T55/49) which is then sent to the tachometer within the instrument cluster.

1. Engine Speed Sensor

It is located on the outside of the transmission just above the flywheel ring gear the G28 Engine Speed Sensor sends an electrical signal to ECU pin T55/49 through an uncolored wire. The ECU uses this information to regulate boost and fuel. It also sends an indication to the G5 Tachometer in instrument cluster.

The sensor serves as a reference point to connect with the G40 Camshaft Position Sensor. The ecu must know when the crankshaft reached TDC, and where the camshaft lies so that it can activate the spark and injectors.

If this sensor fails, the ECU will display a P00160 code which means the Crank Shaft and Intake Camshaft are not in sync and could indicate chain stretch or a jumped link on the upper timing chain. However the code will not appear on its own, without additional information from other sensors (G4 and G40).

It is a little tricky to test since there are several pins on the connector, and each has its own functions. The most effective method to test it is to measure the resistance between the ECU and the sensor. It should read about 1000 ohms if the sensor is at full operation. If you're experiencing issues with this part, check for signs of coolant or oil in the connector bay.

2. Injectors

Yesterday, when i was accelerating to the fullest speed from highway paytoll i had an abrupt drop in power as if the engine was running out of gas or the injectors aren't firing any more. Today, i pulled out the spark plugs, three were drenched with gazoline the 4th one was dry. I put tissue over each injector hole and when i start the engine with no sparks, the ones that have gazoline pop right out. The 4th one remains closed. I checked the ground connection of ECU pins 14,30 and 48/55. I found zero ohm. Therefore, i think the issue is elsewhere.

I also tried to reset the PID with no success. The car will start when the G28 is unplugged, and Key For Audi it is running fine with the G28 connected. However, the intermittent misfire problem still occurs at higher RPM. The temperature sensor for coolant (G62) shows the wrong temp value -49c even when i unplug it. I also noticed that the gauge key for Audi oil pressure in the cockpit shows 2 bar while the actual pressure is 0.0 if i crank up the engine.

I don't know what to do. I believe that I've eliminated everything else. I'm concerned that i may have missed something. If anyone has any ideas please let me know! TIA!

3. Fuel Pump

The fuel pump in the g28 receives a signal from 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 upwards). 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 to make decisions about timing of the fuel injectors, etc. It uses a Crank Position Sensor G4 and an Engine Speed Sensor G28 to achieve this. If you encounter a problem with either of these, the diagnostic scanner will display the codes that could trigger an engine shutdown.

The signs of a failed G28 sensor include an inaccurate gearbox rev counter, gears shifting quicker than normal and/or misfiring when you are in gear. It is likely that your sensor is failing and requires to be replaced if you notice any of these signs. The good news is they are quite affordable and easy to find particularly when you're looking at an Bosch model, which is what we have. Alternatively, the GM version of this unit is also a good option.

5. Tachometer

A damaged engine sensor could cause a number of problems in your vehicle. It's an essential component of the Audi's transmission since it relays information to the ECU about how fast or slow the vehicle's crankshaft is spinning. If the sensor fails, it could cause problems for the transmission as well as 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. It sends a signal directly to the ECU at pin T55/49 through a grey wire. The ECU uses this signal to regulate the amount of fuel and boost, as well as 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. You can also check continuity between ECU pin T55/49 and the instrument cluster connection on pin T6a/1 (trace [79trace [79]) and between pin T6a/1 and the instrument cluster pin T26a/12. It should show around 1000 ohms of resistance between those two pins. This part is common across the replacement audi key 80-100-200-RS2 model, ranging from the 1985 MC all the way up to the 1997 UrS AN and the 1995 RS2 Du You may also find them in wrecking yards.