Faulty timing reference sensor (camshaft or crankshaft position sensor) producing an erratic signal; Damaged or corroded wiring or connector at the sensor or ECM; Electrical interference or poor ground connection affecting the signal; Worn or damaged reluctor wheel (tone ring) or sensor gap misalignment; Failed ECM (less common, but possible after other causes are ruled out)

DTC codes / P03xx · Ignition system and misfire / P0378

P0378Timing Reference High Resolution Signal 'B' Intermittent/Erratic Pulses

P0378 means the engine control module (ECM) has detected intermittent or erratic pulses from the 'B' high-resolution timing reference signal, which is generated by the camshaft or crankshaft position sensor. The ECM uses this signal to precisely synchronize fuel injection and ignition timing, so erratic pulses can disrupt engine operation.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaIgnition system and misfire

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
Engine may hesitate, stumble, or misfire under acceleration or load
Rough idle or unstable engine speed
Difficulty starting or extended cranking time
Reduced engine power or limp mode in some vehicles
In rare cases, the engine may stall unexpectedly

Common causes, most likely first

Faulty timing reference sensor (camshaft or crankshaft position sensor) producing an erratic signal
Damaged or corroded wiring or connector at the sensor or ECM
Electrical interference or poor ground connection affecting the signal
Worn or damaged reluctor wheel (tone ring) or sensor gap misalignment
Failed ECM (less common, but possible after other causes are ruled out)

How to diagnose and fix it

Inspect the sensor and its wiring for obvious damage, corrosion, or loose connections
Check the sensor gap and reluctor wheel for debris or damage
Perform a wiggle test on the sensor harness while monitoring live data to detect intermittent faults
Measure the sensor's resistance and compare to manufacturer specifications
Use an oscilloscope to verify the signal waveform for consistency and amplitude
Repair or replace damaged wiring or connectors as needed
Replace the timing reference sensor if it fails testing, then clear codes and verify the repair

Intermittent Timing Signal Diagnostics

A loose or corroded ground connection at the engine block can cause erratic sensor signals that mimic a failing sensor.
Aftermarket electrical accessories or poor shielding can introduce interference into the sensor circuit, leading to intermittent pulses.
The code may set only under specific conditions such as high engine load or temperature, so intermittent faults often require data logging during a test drive.
A worn reluctor wheel or excessive sensor gap can produce erratic pulses without the sensor itself being faulty.
Always check for related codes like P0335 or P0340, as multiple timing codes can indicate a shared wiring or mechanical issue.

Can I keep driving with P0378?

If the check engine light is on but the engine runs smoothly, you can drive cautiously to a repair shop, but avoid aggressive acceleration or heavy loads. If the engine runs rough, misfires, or stalls, stop driving and have the vehicle towed to prevent damage or safety risks.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.