P0377
UniversalTiming Reference High Resolution Signal B Too Few Pulses
The engine control system detected fewer pulses than expected from the high-resolution timing reference signal B. This signal helps the system track engine timing and speed. A weak, interrupted, or otherwise incorrect signal can affect starting or engine operation, but the code alone does not identify a failed part.
⚠️ Before You Begin (Safety First)
If the engine stalls, runs very roughly, or becomes difficult to control, pull over safely and stop driving; arrange diagnosis or towing. If the vehicle runs normally, drive cautiously and get the fault checked soon.
Common Symptoms
- The check-engine light may be on, with no noticeable change in how the vehicle runs.
- Hard starting or a no-start condition may occur if the engine control system cannot reliably track timing.
- Rough running, misfires, or reduced performance may occur if the timing reference signal is intermittent or inaccurate.
- The engine may stall if the signal drops out while driving.
Common Causes
- A timing-reference sensor or related signal source may produce a weak, interrupted, or incomplete signal.
- Damaged, loose, corroded, or poorly connected wiring or connectors may interrupt signal B.
- A damaged or contaminated timing target may prevent the signal source from registering all expected pulses.
- A power, ground, or control-system fault may affect signal generation or interpretation.
Diagnostic Steps
- Check whether the engine runs roughly, stalls, or is difficult to start; avoid driving if those symptoms make the vehicle unsafe.
- With the engine off, visually inspect accessible timing-reference wiring and connectors for looseness, corrosion, or visible damage; do not pull on wiring or probe terminals.
- Use a compatible scan tool to record other codes and available freeze-frame information, since related faults or operating conditions can help guide diagnosis.
- Have a qualified technician test the signal and circuit using service information specific to the vehicle before replacing parts.
When to Call a Professional
A technician can compare scan data with the timing-reference signal, inspect related wiring and connectors, and test the signal and its circuit using vehicle-specific service information. Further checks may be needed to distinguish a sensor or target issue from wiring, power, grounding, or control-system problems.
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Commonly Asked Questions
Does P0377 prove that the timing-reference sensor needs replacement?
No. It reports too few pulses on timing reference signal B. The cause could be the signal source, wiring, connector, timing target, or another circuit or control-system issue.
Can the vehicle still be driven with this code?
That depends on how the engine behaves. If it stalls, runs very roughly, or is hard to control, stop driving and arrange assistance. If it runs normally, drive cautiously and have it diagnosed soon.
Why might there be no noticeable symptoms?
The fault may be intermittent or may not substantially affect engine operation under the conditions in which the vehicle is being used.
What does signal B identify?
The code identifies a high-resolution timing-reference signal designated B, but it does not by itself specify the component location or the vehicle-specific signal arrangement.
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