P0378 means the engine control module has detected intermittent or erratic pulses from the 'B' high-resolution timing reference sensor circuit, which provides critical crankshaft or camshaft position data. Because this signal is used to time fuel injection and ignition, an unstable signal can cause drivability problems or a no-start condition.
The crankshaft or camshaft position sensor that generates Signal B can develop internal faults, producing missing or irregular pulses as it heats up or vibrates.
Chafed, corroded, or loose wires and terminals can cause momentary opens, shorts, or electrical noise that interrupts the high-resolution signal.
A cracked, chipped, bent, or debris-covered tone ring changes the magnetic or optical pattern seen by the sensor, causing erratic pulse output.
A loose, misaligned, or improperly seated sensor alters the distance to the tone wheel, weakening or distorting the signal.
Poor power or ground supply to the sensor from shared circuits can make the signal unstable even if the sensor itself tests good.
A rare failure of the engine computer's input processing circuit can misread a good sensor signal; this should only be considered after sensor and wiring checks are ruled out.
No. Most instances are caused by a failing position sensor, wiring or connector problems, or a damaged reluctor wheel. PCM replacement is rarely the correct fix.
It is not advisable. Erratic timing signals can cause stalling, hesitation, or a sudden no-start, especially at speed or under load.
Signal B is manufacturer-defined and usually refers to a high-resolution crankshaft or camshaft position sensor; consult the service information for the specific engine.
Heat, vibration, and movement often make a marginal sensor, loose connector, or chafed wire fail only under certain driving conditions.