How to Replace an Audi G28 Engine Speed Sensor

In this video, Charles the Humble Mechanic shows how to replace the G28 engine speed sensor. The sensor is situated at the top of the transmission above the flywheel ring gear. It transmits a signal to the ECU via an uncolored wire T55/49, then to the tachometer located on the instrument cluster.

1. Engine Speed Sensor

The grey wire is situated on the edge of transmission, above the flywheel ring. The sensor transmits an electrical signal through the grey wire to pin T55/49. The ECU utilizes this information to regulate boost and fuel. It also sends an indication to the G5 Tachometer within the instrument cluster.

The sensor is used to connect the G40 Camshaft position Sensor. The ecu has to know when the crankshaft has reached TDC, and the position of the camshaft, in order to activate the spark and injectors.

If this sensor fails when it fails, the ECU will display a P00160 error code. This indicates that the Crank Shaft is not in alignment with the Intake Camshaft. It could also be a sign of an issue with the chain or a jumped chain link in the upper chain. The code will not appear without the additional information provided by other sensors (G4 or G40).

It’s a bit tricky to test since there are different pins on the connector and each has its own functions. The best way to do it is by measuring the resistance between the ECU and the sensor. When the sensor is fully functional, it should read approximately 1000 ohms. Look for evidence of coolant or oil in the connector bay if you are experiencing issues with this part.

2. Injectors

Yesterday, when accelerating from highway paytoll at a high speed, i noticed a huge drop in power. It was as if the engine was running out of gas. Or my injectors weren’t firing. Today, i pulled out the spark plugs. Three were drenched in gazoline, the fourth one was dry. When I crank the engine, there are no sparks, I put a piece of tissue on the top of each hole in the injector and the 3 that were drenched in gazoline jump out but the 4th stay shut. I tested the ground connection of ECU pins 14,30, and 48/55. I got zero ohm. audi a3 key replacement g28carkeys.co.uk assume that the problem is in another location.

I also tried to reset the PID without success. The car will start when the G28 is disconnected, but it works fine when the G28 connected. However the intermittent misfire issue still occurs at higher RPM. The coolant sensor (G62), even if it is not plugged in, shows a temperature of -49c. I also noticed that the oil pressure gauge in the cockpit is showing 2 bar while the actual pressure is 0.0 when I crank up the engine.

I’m not sure what to do. I feel like i’ve pretty much ruled everything else out. I’m afraid i may have missed something. If anyone has any suggestions, please chime in! TIA!

3. Fuel Pump

The fuel pump on the g28 is activated by a signal by the RPM sensor. The GM-style sender is the same as the G4 and they both work in the 80 100 200, UrS and RS2 cars which is why you can easily locate one at a wrecking yard or in a local parts store. It is easy to test them – simply switch your DMM into resistance mode and determine the distance between pins 1 and 2 (with the bump at the connector’s end facing up). They must be infinite Ohms.

4. ECU

Our 20vt turbo (3B AAN, ABY, and ADU) engines are equipped with an ECU that has to know the speed and position of the crankshaft to make a decision about timing of the fuel injectors, etc. To accomplish this, it utilizes a Crank Position Sensor (G4) and an Engine Speed Sensor (G28). If you encounter a problem with either of these, the diagnostic scanner will show codes that could lead to the engine shutting down.

A malfunctioning G28 sensor can cause an inaccurate speed counter for the gearbox and a gearbox which shifts faster than normal, or an unfire when in gear. If you have any of these issues it is most likely that your sensor is failing and should be replaced. The good thing is that they are very cheap and easy to find particularly if you’re looking at an Bosch unit which is what we have. You can also choose the GM version of this component is also a good option.

5. Tachometer

A malfunctioning engine speed sensor could be the reason behind many problems in 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 car’s crankshaft is rotating. This sensor could cause the transmission to malfunction and other components in the car to be affected.

The G5 engine speed sensor is situated on the edge of the transmission just above the flywheel ring gear and sends a signal directly to the ECU at pin T55/49, via an uncolored wire. The ECU then uses and processes this signal to regulate fuel, timig and boost as well as sends it on to the G5 Tachometer located in the instrument cluster. You can check 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. It should show approximately 1000 ohms of resistance between these two points. This is a common feature across the Audi 80-100-200-RS2 series, starting beginning with the 1985 MC and up to the 1997 UrS AN and the 1995 RS2 DU, so you might find some good ones in wrecking yards.