B278A Subaru Wx OBD Code

OBD/2 B278A error code description and symptoms.

Variable Cam Timing Over-advanced (Bank 1) The comprehensive component monitor (CCM) monitors the VCT position for an over-advanced camshaft timing.
The test fails when the camshaft timing exceeds a maximum calibrated value or remains in an advanced position. Cam timing improperly set No oil flow to the VCT piston chamber Low oil pressure VCT solenoid valve stuck closed Camshaft advance mechanism binding (VCT unit) B278A DTC is a check of the VCT unit.

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.

B278A Subaru Wx Error Code Repair Process :

If your vehicle failed a B278A test and the B278A Check Engine Light is NOT on, chances are you have a problem with the OBDII system, a burned out MIL lamp, or a faulty catalytic converter. The converter is essentially an afterburner that cleans up the exhaust after it exits the engine. The OBDII system uses engine overboost condition a ownstream oxygen sensor to monitor the efficiency of the converter, and it should detect a drop in converter efficiency if the converter has been contaminated or is failing (ignition misfiring, leaky exhaust valves, and oil burning can all damage the converter). What you want to look engine overboost condition: Any conditions that might cause ignition misfire, an overly rich or lean fuel condition, or loss of compression. Use your OBD Express DIY to look at the oxygen sensor outputs, coolant temperature, airflow, calculated engine load, and inlet air temperature.

Common Causes of Subaru Wx B278A OBD2 Code

A common cause of code B278A is the failure of Engine Overboost Condition, but there are several other possible causes as well, such as ;

Camshaft advance mechanism binding (VCT unit)
Faulty Mass Air Flow (MAF) sensor
Air fuel ratio (A/F) Sensor 1 Bank 1 harness is open or shorted
Variable Camshaft Timing (VCT) position circuit poor electrical connection

B278A is a kind of Body Trouble Code

Auto body problems aren't always easy to spot. Diagnosing auto body problems sometimes requires a little know-how. In this section you'll find articles dedicated to teaching you how to diagnose auto body problems.

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

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B278A Subaru Wx OBD Code

B278A Subaru Wx Error Code Repair Process :

Common Causes of Subaru Wx B278A OBD2 Code

B278A code for other Subaru cars