U3991 Mitsubishi Valley OBD Code

OBD/2 U3991 error code description and symptoms.

The Transmission Fluid Pressure Switch allows the engine's control module (PCM) or Transmission Control Module (TCM) to use hydraulic fluid to engage the clutches in the transmission to allow for smoother shifting while driving. If the PCM or TCM detects an issue with the hydraulic clutch or the pressure switch, the PCM or TCM will set code U3991

One example of this would be when an automatic vehicle in placed in gear. To prevent the added drag from the torque converter and transmission from reducing the idling speed, the PCM will command the idle control valve to allow more air to enter the engine, while at the same time, adjusting the injector pulse width to inject more fuel to suit the increased amount of air. Note that the idle air control valve is closed by the PCM when the throttle plate is opened to prevent excess air from entering the engine.

U3991 Mitsubishi Valley Error Code Repair Process :

If your air temperature external sensor circuit open check engine light is illuminated, it's best to take it in for diagnostic testing, which can feel like a hassle. Because while the lights vary in appearance from vehicle to vehicle, all have the same basic meaning: There's a problem with the car's emissions system. The on-board diagnostics system U3991 and engine control unit are in charge of monitoring a bunch of different air temperature external sensor circuit open, and if they get a reading that's a little out of whack, up pops the check engine light.

Common Causes of Mitsubishi Valley U3991 OBD2 Code

A common cause of code U3991 is the failure of Air Temperature External Sensor Circuit Open, but there are several other possible causes as well, such as ;

Continuous oil flow to the VCT piston chamber
Faulty Camshaft Position Sensor
Ignition coils circuit poor electrical connection
Improper ignition timing

U3991 is a kind of Network Trouble Code

U-code indicates that engine communication errors and shows lost communication with engine parts.U-Codes are fairly straight forward, given all of the articles and technical publications that have been written regarding these problematic codes. In most cases, it just comes down to identifying the module that isn't communicating with the other modules on the CAN bus line for whatever reason.

Engine OBD 2 Codes website is a freeware resource center for engine trouble codes.

About Us | Contact | Privacy

U3991 Mitsubishi Valley OBD Code

U3991 Mitsubishi Valley Error Code Repair Process :

Common Causes of Mitsubishi Valley U3991 OBD2 Code

U3991 code for other Mitsubishi cars