U3904 Engine Code Repair

Meaning of U3904 engine trouble code is a kind of network trouble code and U3904 code can be about replacing a broken oxygen sensor can eventually lead to a busted catalytic convertor which can cost upwards of $2,200. Taking your car into a shop will cost you around $210 depending on the car. However, an oxygen sensor is easy to replace on many cars and is usually detailed in the owner's manual. If you know where the sensor is, you only have to unclip the old sensor and replace it with a new one. Regardless of how you approach it, you should get this fixed right away.

U3904 Fault Symptoms :

U3904 Possible Solution:

Air Conditioning Pressure Sensor (ACP) Insufficient Pressure Change Each time the A/C clutch engages, the PCM is looking for a pressure change in the refrigerant. If the change in pressure is outside of the calibration the DTC will set. A/C system mechanical failure Open ACP or VREF circuit A/C sensor damaged A/C system electrical failure A/C clutch always engaged Verify A/C system function, including refrigerant charge.

U3904 Code Meaning :

The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate.

U3904 DTC reports a sensor fault, replacement of the sensor is unlikely to resolve the underlying problem. The fault is most likely to be caused by the systems that the sensor is monitoring, but might even be caused by the wiring to the sensor itself.