What Does P0378 Mean?
The ECM has detected an intermittent or erratic pulse pattern from the timing reference high-resolution signal B. Unlike a complete failure, this code indicates the signal comes and goes unpredictably, making it particularly difficult to diagnose. The driver may experience sporadic misfires, brief hesitations during acceleration, or occasional rough idle that comes and goes with no clear pattern.
Common Causes
35%
Intermittent wiring fault in the sensor B circuit caused by vibration-induced breaks or loose connections
25%
Temperature-sensitive sensor B failure that acts up when hot or cold
20%
Corroded connector causing intermittent high-resistance contact
10%
Intermittent ground fault in the sensor B return circuit
10%
Flexing reluctor ring or loose tone wheel with intermittent air gap variation
Diagnostic Steps
1
Set up continuous data logging of the sensor B signal and RPM PID. Drive the vehicle under various conditions (cold start, warm-up, highway, stop-and-go) to capture the intermittent fault occurrence.
2
Perform a comprehensive wiggle test on the entire sensor B circuit from the sensor connector through the engine harness to the ECM connector. Monitor the oscilloscope waveform continuously while flexing, tapping, and pulling each section.
3
Inspect all connector pins for the sensor B circuit using a magnifying glass or inspection camera. Look for backed-out pins, corroded contacts, or spread terminal ends that could cause intermittent contact.
4
With the engine running, use a heat gun and freeze spray alternately on the sensor itself to determine if the fault is temperature-related. Monitor the signal for dropouts during thermal cycling.
5
Check the reluctor ring mounting by attempting to move it by hand with the engine off. Any looseness will cause intermittent air gap changes and erratic signals. Verify all tone wheel fasteners are tight.
Estimated Repair Cost
$100 - $550
Parts + labor, varies by vehicle and location
The ECM has detected an intermittent or erratic pulse pattern from the timing reference high-resolution signal B. Unlike a complete failure, this code indicates the signal comes and goes unpredictably, making it particularly difficult to diagnose. The driver may experience sporadic misfires, brief h...
The most common cause of P0378 (Timing Reference High Resolution Signal B Intermittent/Erratic Pulses) is: Intermittent wiring fault in the sensor B circuit caused by vibration-induced breaks or loose connections
Typical repair costs for P0378 range from $100 to $550, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Intermittent timing signal issues can cause unpredictable stalling, which is hazardous during highway driving or in traffic. Because the fault is intermittent, it may worsen suddenly. Schedule diagnosis promptly; if stalling occurs, avoid driving until repaired.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0378 to identify the root cause.
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Quick Info
Category
Powertrain
System
Ignition / Engine Timing System
Difficulty
Type
Generic (SAE)
Recommended Tools
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