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How to Replace an audi spare key 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 sends a signal to the ECU via the grey wire (T55/49) which is then sent to the tachometer in 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 signals to ECU pin T55/49 through an uncolored wire. The ECU uses this information to control boost and fuel. It also sends an indication to the G5 tachometer in the instrument cluster.

The sensor is used to correlate with the G40 Camshaft position Sensor. The ecu needs to know when the crankshaft is TDC and where the camshaft is so it can start spark and injectors according to the situation.

If this sensor fails, the ECU will display a P00160 code which means the Crank Shaft and Intake Camshaft are out of sync, possibly indicating chain stretch or a jumped link on the upper timing chain. The code won't appear without the additional information provided by other sensors (G4 or G40).

It can be a bit difficult to test since there are different pins on the connector, and each one has different functions. The best way to do it is by measuring the resistance between the ECU and the sensor. It should read approximately 1000 ohms when it is at full operation. Examine for signs 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 full speed I noticed a significant reduction in power. It was as if the engine was running out of gas. Or, my injectors weren't firing. I pulled out the spark plugs this morning, three were drenched in gasoline and the 4th was dry. I placed a tissue over each injector hole, and when I turn the engine on without sparks, the 3 with gazoline jump right out. The fourth one remains shut. I tried to test the ground connections of ECU pins 14,30 and 48/55. I got 0ohm. I'm assuming that the issue is somewhere else.

I also tried to reset PID without success. The car will start when the G28 is disconnected, but it runs fine with the G28 connected. However the intermittent misfire issue still occurs at higher RPM. The coolant temperature sensor (G62) shows the wrong temperature of -49c even when i unplug it. I also noticed that the oil gauge in the cockpit shows 2 bars when the actual pressure is zero.

I'm not certain what to do, but i believe that i've eliminated everything else. 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 can be activated by a signal from the RPM sensor. The GM-style transmitter functions similarly to the G4 sender and audikey works on the 80,100,200, UrS, and RS2 vehicles. You can easily locate an extra in a wrecking shop or a parts store. It is simple 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 up). They should be infinite Ohms.

4. ECU

Our 20vt turbo (3B, AAN, ABY and ADU) engines are equipped with an ECU that must know the speed and position of the crankshaft in order to make a decision about timing of the fuel injector, for example. 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 one of these, the diagnostic scanner will show codes that could lead to an engine shut down.

A damaged G28 sensor could result in an inaccurate speed counter for your gearbox or a gearbox that shifts more quickly than normal, or an unfire when in gear. If you are experiencing any of these issues it is likely that your sensor is deteriorating and needs replacing. The good news is that they are very affordable and easy to find particularly in the case of the Bosch unit which is what we have. If you prefer, GM's version of this component is an option.

5. Tachometer

A malfunctioning engine speed sensor could be a cause for many issues in your vehicle. It's an essential component of the transmission in your audi keys, as it transmits information to the ECU about how fast or slow the car's engine is turning. If this sensor fails, it will affect the performance of the transmission, as well as the rest of the car's components.

The G5 engine sensor is located at the edge of the transmission, just above the flywheel ring. It transmits a signal via a gray wire to the ECU pin T55/49. The ECU utilizes this signal to control fuel and boost, as well as timig. It also relays 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, between ECU pin T55/49 and the instrument cluster connection to pin T6a/1 (trace [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 two points. This is a typical part across the audi keyless entry 80 100 200, UrS and RS2 range from 1985 MC through the 1997 UrS AAN and 1995 RS2 ADU. Good ones might be availble in wrecking yards.