How to Replace an Audi G28 Engine Speed Sensor
Charles the Humble Technician teaches how to replace the G28 Engine Speed Sensor. This sensor is situated at the edge of transmission just above the flywheel gear. It transmits a signal to the ECU through a grey wire T55/49, then to the tachometer in 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 via the grey wire. The ECU then utilizes this information to regulate fuel, timig and boost. It also sends an indication to the G5 Tachometer located in the instrument cluster.
The sensor is used to connect the G40 Camshaft position Sensor. The ecu must be aware when the crankshaft is TDC and where the camshaft is located so that it can trigger spark and injectors accordingly.
If this sensor fails, the ECU will display an error code P00160. 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 won't appear without the additional information supplied by other sensors (G4 or G40).
It can be a bit difficult to test since there are various pins on the connector, and each one has different functions. The best method for doing this is to measure the resistance between the ECU and the sensor. It should read about 1000 ohms if the sensor is in full operation. If you are having problems with this sensor, look for signs of oil or coolant in the connector bay.
2. Injectors
Yesterday, when i was accelerating to the fullest speed from highway paytoll, i experienced a big cut in power like the engine is running out of gas or injectors aren't firing anymore. I took out the spark plugs this morning and found that 3 were soaked with gasoline and the 4th was dry. When I start the engine with no sparks, I put a piece of tissue on the top of each of the injector holes, the 3 drenched with gazoline pop out, but the 4th one stays shut. I inspected the ground connection on ECU pins 14/55, 30/55 and 48/55. I got 0ohm. I'm assuming the issue is elsewhere.
I also tried to reset PID without success. The car is able to start when the spare audi key G28 is not plugged in and it runs perfectly when it is plugged in, but audi keys still has intermittent misfire issues at higher RPM. The coolant sensor (G62), even when it is unplugged, shows an ice temperature of -49c. I also noticed that the oil gauge in the cockpit shows 2 bar when the actual pressure is 0.
I'm not sure what to do. I think I've ruled everything else out. I'm concerned website that i may have missed something. If anyone has any suggestions, please let me know! TIA!
3. Fuel Pump
The fuel pump in the g28 is activated by a signal sent by the RPM sensor. The GM-style sender website is identical to the G4 and both are used in the 80, 100, 200, UrS and RS2 cars so you can easily find one at a salvage yard or in a local parts store. Testing them is easy to do - just put your DMM in resistance mode and measure the resistance between pins 1 (with the bump on the connector end up) and 2 (2nd from the left on the black end of the connector). They must be infinite Ohms.
4. ECU
The ECU in our 20vt turbo (3B AAN ABY) engines must be aware of the position and speed of the crankshaft to determine timing of fuel injectors, etc. To do this, it makes use of a Crank Position Sensor (G4) and an Engine Speed Sensor (G28). If you have a problem with either one of these, the diagnostic scanner will display the codes that could trigger an engine shut down.
A failing G28 sensor can cause an inaccurate speed counter for the gearbox, a gearbox that shifts more quickly than normal, and/or a misfire in the gear. If you experience any of these issues, it is likely that your sensor is failing and requires replacement. They're cheap and easy to find especially in the case of a Bosch unit like ours. Alternately, the GM version of this component is also a good choice.
5. Tachometer
A malfunctioning engine speed sensor could be a cause for many issues with your car. It's an essential component of the transmission of your Audi because it relays information to the ECU regarding how fast or slow the engine is spinning. This sensor can cause the transmission to malfunction and other car components to be affected.
The G5 engine speed sensor is situated on the edge of the transmission above the flywheel ring gear. It transmits a signal to the ECU at pin T55/49, via a grey wire. The ECU utilizes this signal to control the flow of fuel and boost as well as timig. It also transmits it to the G5 Tachometer located in the instrument cluster. You can check for sensor failure by examining the continuity from the audi advanced key sensor to the tachometer. Also, you can verify continuity between pin T55/49 of the ECU and pin T6a/1 of the instrument cluster (trace [79trace [79]) and between pin T6a/1 and pin T26a/12. There should be an average resistance of 1000 ohms between these points. This is a typical component across the Audi 80, 100, 200, UrS and RS2 range from 1985 MC through the 1997 UrS AAN and 1995 RS2 ADU, so the best parts could be found in wrecking yards.