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. This sensor is situated on the outside of the transmission over the flywheel gear. It sends a signal to the ECU via a grey wire (T55/49), then to the tachometer located in the instrument cluster.
1. Engine Speed Sensor
Located on the edge of the transmission just 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. This Web page sends an indicator to the G5 Tachometer within the instrument cluster.
The sensor is used to correlate the G40 Camshaft position Sensor. The ecu needs to be aware of when the crankshaft has reached TDC and also the position of the camshaft, in order to activate the spark and injectors.
If this sensor fails, the ECU will display the P00160 error, which means the Crank Shaft and Intake Camshaft are out of sync, possibly indicating chain stretch or a jumped link on the upper chain of timing. However, the code won't be displayed on its own without additional information from other sensors (G4 and G40).
Testing is a bit tricky since there are two connector pins and they perform different functions but the best method of testing it is by measuring resistance between the sensor and the ECU. It should read about 1000 ohms when the sensor is at full operation. If you're having issues with this sensor, look for signs of coolant or oil in the connector bay.
2. Injectors
Yesterday accelerating full speed from highway paytoll i had an abrupt drop in power like the engine is running out of gas or injectors are not firing any more. Today, i pulled out the spark plugs, 3 were drenched in gazoline, the fourth one was dry. I put a piece of tissue over each injector hole and when i turn the engine on without sparks, the three with gazoline jump out. The 4th one remains closed. I checked the ground connection on ECU pins 14/55,30/55 and 48/55 I get 0ohm. I assume that the problem is somewhere else.
I also tried to reset the PID without success. The car will start when the G28 is unplugged and it runs perfectly when it is plugged in however it is experiencing intermittent misfires at higher RPM. The coolant sensor (G62), even when unplugged, still shows an ice temperature of -49c. I also noticed that the oil gauge in the cockpit shows 2 bars but the actual pressure is zero.
I'm not sure what to do. I think I've all other possibilities out. But i'm worried that i might have missed something. Please let me know If you have any suggestions! TIA!
3. Fuel Pump
The fuel pump on the g28 is activated by a signal by the RPM sensor. The GM-style sender is identical to the G4 and they both work in the 80 100, 200, UrS and RS2 cars so you can easily find one at a wrecking yard or from a parts store. It is easy to test them - just 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 must be infinite Ohms.
4. ECU
The ECU in our 20vt turbo (3B AAN ABY ADU) engines needs to know both the speed and position of the crankshaft in order to make a decision about timing of fuel injectors, etc. To do this, it uses a Crank Position Sensor (G4) and an Engine Speed Sensor (G28). If either of these go bad you will get codes on the diagnostic scanner that can lead to engine shutdown.
The signs of a malfunctioning G28 sensor include an inaccurate rev counter for the gearbox and gears that shift faster than normal and/or misfiring when you are in gear. It is likely that the sensor is failing and needs to be replaced if you notice any of these signs. The good news is they are very cheap and readily available, especially in the case of the Bosch model, which is what ours are. You can also choose the GM version of this component is also a good choice.
5. Tachometer
A damaged engine sensor could cause a number of problems in your car. It's an essential component of the transmission in your Audi because it relays information to the ECU about how fast or slow the engine is spinning. This sensor can cause the transmission to malfunction and other components of the car to be affected.
The G5 engine sensor is located near the edge of the transmission, over the flywheel ring. It sends signals via an uncolored wire to the ECU pin T55/49. The ECU is then able to process the signal to control the flow of fuel, timig and boost and then sends it on to the G5 tachometer in the instrument cluster. You can determine if the sensor is in failure by examining the continuity of the sensor to the tachometer. You can also verify continuity between pin T55/49 of the ECU and pin T6a/1 of the instrument cluster (trace [79]), and between pin T6a/1 and pin T26a/12. You should see around 1000 ohms of resistance between those two pins. This is a common component across the Audi 80, 100 200, UrS and RS2 range from 1985 MC until the 1997 UrS AAN and 1995 RS2 ADU, so the best ones could be available in wrecking yards.