What Does P0377 Mean?
The ECM has detected that the timing reference high-resolution signal B is producing too few pulses relative to what is expected for the engine's reluctor wheel configuration. This means the sensor is missing tooth transitions, which could be caused by a physical gap in the reluctor ring, a weak sensor signal, or excessive sensor-to-reluctor distance. The engine may run with degraded timing accuracy, misfire, or stall intermittently.
Common Causes
30%
Excessive air gap between sensor B and the reluctor ring causing weak signal amplitude
25%
Weakened or failing sensor B with reduced output voltage
20%
Damaged reluctor ring with missing or heavily worn teeth
15%
High resistance in the sensor B signal circuit reducing signal amplitude below ECM detection threshold
10%
Contamination on the reluctor ring or sensor face reducing magnetic coupling
Diagnostic Steps
1
Using an oscilloscope, capture the sensor B waveform and verify the signal amplitude meets the minimum ECM threshold (typically >0.3V AC for magnetic sensors at idle). Compare amplitude to sensor A if available.
2
Measure the sensor B air gap with a non-magnetic feeler gauge. Compare to manufacturer specification (typically 0.5-1.5mm). Adjust or replace the mounting hardware if out of spec.
3
Inspect the reluctor ring teeth for heavy wear, chips, or missing sections. Rotate the engine by hand while watching the oscilloscope waveform to identify any specific tooth positions where signal drops out.
4
Measure the total circuit resistance from ECM connector pins to sensor B pins. Total resistance should closely match the sensor's internal resistance with minimal additional wire resistance (<2 ohms added).
5
Clean both the sensor face and reluctor ring teeth with brake cleaner and a non-metallic brush to remove oil, grease, or metallic buildup that could reduce the magnetic field coupling.
Estimated Repair Cost
$100 - $550
Parts + labor, varies by vehicle and location
The ECM has detected that the timing reference high-resolution signal B is producing too few pulses relative to what is expected for the engine's reluctor wheel configuration. This means the sensor is missing tooth transitions, which could be caused by a physical gap in the reluctor ring, a weak sen...
The most common cause of P0377 (Timing Reference High Resolution Signal B Too Many Pulses) is: Excessive air gap between sensor B and the reluctor ring causing weak signal amplitude
Typical repair costs for P0377 range from $100 to $550, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Missing timing pulses degrade the ECM's ability to calculate accurate crankshaft position, leading to timing errors and potential misfires. The engine may stall unexpectedly. Have the vehicle diagnosed soon; avoid highway driving if stalling occurs.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0377 to identify the root cause.
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Quick Info
Category
Powertrain
System
Ignition / Engine Timing System
Difficulty
Type
Generic (SAE)
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