What Does P0379 Mean?
The ECM has detected intermittent or erratic pulses from the timing reference high-resolution signal B. This is a secondary qualifier code indicating the B-circuit timing sensor signal is cutting in and out or producing noisy, unstable waveforms. The engine may exhibit intermittent misfires, slight hesitations, or occasional rough running episodes that clear on their own before returning.
Common Causes
30%
Crankshaft position sensor B developing internal intermittent open circuit
30%
Chafed or pinched wiring in the sensor B harness from engine movement or improper routing
20%
Loose or contaminated sensor B electrical connector
10%
Reluctor ring wobble or endplay causing variable sensor air gap
10%
EMI from failing alternator diodes inducing noise on the sensor signal
Diagnostic Steps
1
Review freeze frame data to identify engine conditions (RPM, load, temperature) when the fault occurred. This helps determine if the issue is speed-related, temperature-related, or load-related.
2
Perform a dual-channel oscilloscope comparison of sensor A and sensor B waveforms simultaneously. Run the engine at various speeds and look for amplitude or pattern differences between the two signals.
3
Disconnect the alternator and briefly run the engine on battery to determine if alternator AC ripple noise is the cause. If the signal cleans up, test alternator diode output with an AC voltmeter (should read <0.5V AC across the battery).
4
Inspect the full wiring route from sensor B to the ECM, paying particular attention where the harness crosses moving parts, sharp edges, or heat sources. Look for signs of intermittent contact from vibration.
5
Check crankshaft endplay with a dial indicator (typical spec 0.05-0.30mm). Excessive endplay changes the sensor air gap during operation, causing intermittent signal variations.
Estimated Repair Cost
$100 - $600
Parts + labor, varies by vehicle and location
The ECM has detected intermittent or erratic pulses from the timing reference high-resolution signal B. This is a secondary qualifier code indicating the B-circuit timing sensor signal is cutting in and out or producing noisy, unstable waveforms. The engine may exhibit intermittent misfires, slight ...
The most common cause of P0379 (Timing Reference High Resolution Signal B Intermittent/Erratic Pulses) is: Crankshaft position sensor B developing internal intermittent open circuit
Typical repair costs for P0379 range from $100 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Erratic timing signals can cause unpredictable engine behavior including stalling. The intermittent nature makes the fault unpredictable. Avoid highway driving until the fault is diagnosed. If the vehicle stalls during operation, do not continue to drive.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0379 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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