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How to Replace an audi a1 key fob G28 Engine Speed Sensor

In this video Charles the Humble Mechanic shows how to replace the G28 engine speed sensor. This sensor is situated at the edge of transmission over the flywheel gear. It sends a signal to the ECU via the grey wire (T55/49) and then to the tachometer within the instrument cluster.

1. Engine Speed Sensor

Located on the edge of the transmission, above the flywheel ring gear, the G28 Engine Speed Sensor sends an electrical signal to ECU pin T55/49 through the grey wire. The ECU uses this information to regulate fuel and boost. It also sends signals to the G5 tachometer in the instrument cluster.

The sensor is used as a reference point to connect with the G40 Camshaft Position Sensor. The ecu needs to know when the crankshaft is TDC and where the camshaft is so it can activate spark and injectors in the right way.

If this sensor fails, the ECU will show an error code P00160 which indicates that the Crank Shaft and Intake Camshaft aren't in sync and could indicate the chain is stretched or a jump link on the upper chain of timing. However, the code won't appear on its own without additional information from other sensors (G4 and G40).

Testing can be a bit difficult because there are two connector pins, and they perform different functions but the best method of testing it is to measure resistance between the sensor and the ECU. If the sensor is operational, it should read about 1000 ohms. Look for evidence of coolant or oil in the connector bay if you have problems with this part.

2. Injectors

Yesterday, as i was accelerating off the highway paytoll at maximum speed I noticed a significant drop 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 and found that 3 were soaked in gasoline, and the fourth was unclean. When I crank the engine with no sparks, I put a piece of tissue on the top of each hole in the injector and the 3 drenched with gazoline pop out, but the 4th stay closed. I inspected the ground connection on ECU pins 14/55,30/55 and 48/55 I get zero ohm. I think the issue is somewhere else.

I also tried to reset the PID but with no luck. The car will start when the G28 is disconnected, but it is running 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 that is -49c even after unplugging it. Also, i noticed that the gauge for oil pressure in the cockpit shows 2 bar when the actual pressure is 0.0 when i rev the engine.

I don't know what to do. I believe that I've all other possibilities out. I'm afraid i may have missed something. Please let me know should you have any suggestions! TIA!

3. Fuel Pump

The fuel pump in the g28 can be activated by a signal sent by the RPM sensor. The GM-style sensor is identical to the G4 and both function 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 - simply switch your DMM into resistance mode and determine the distance between pins 1 and 2 (with the bump on the connector's edge facing up). They should be infinite Ohms.

4. ECU

The ECU in our 20vt turbo (3B AAN ABY ADU) engines must know both the position and speed of the crankshaft to determine fuel injector timing, 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 lead to the engine shutting down.

A damaged G28 sensor can cause an inaccurate speed counter for your gearbox, a gearbox that shifts faster than normal, and/or a misfire in the gear. If you experience any of these issues it is most likely that your sensor is going bad and should be replaced. They are cheap and easy-to-find particularly in the case of a Bosch unit like ours. Alternately, GM's version this component is an option.

5. Tachometer

A failing engine sensor could cause a myriad of issues within your vehicle. It's a crucial component of the transmission in your audi a3 Spare key since it sends information to the ECU on how fast or slow the engine is turning. This sensor could cause the transmission to fail and other components of the car to be affected.

The G5 engine sensor is located at the edge of transmission, audi A3 spare key above the flywheel ring. It transmits an electrical signal through gray wire to ECU pin T55/49. The ECU then processes this signal to regulate fuel, timig, and boost and then transmitting it to the G5 tachometer inside 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 on pin T6a/1 (trace [79]) as well as between T6a/1, and the instrument cluster pin T26a/12. You should observe approximately 1000 ohms resistance between those points. This is a common feature across the Audi 80-100-200-RS2 range, from the 1985 MC up to the 1997 UrS AN and the 1995 RS2 DU, so you might find good ones in wrecking yards.