P0377
Timing Reference High Resolution Signal B Too Few Pulses
Ignition / timing reference
Generic OBD-II
High
What it means
P0377 means the ECM counted fewer pulses than expected on the 'B' high-resolution timing reference signal — a precise crank/cam signal used to time fuel and spark. Too few pulses, usually from a failing sensor, a damaged reluctor wheel, or wiring trouble, disrupts engine timing and can cause misfires, rough running, hard starting, or stalling.
High
Can I keep driving? May run rough, stall, or fail to start; treat as a timing fault and get it diagnosed before driving far.
Common symptoms
What you'll notice
- Check-engine light on
- Misfire and rough running
- Hard starting or stalling
- Reduced power and hesitation
Common causes
Most likely first
- Faulty high-resolution timing (optical) sensorLikely
- Faulty camshaft or crankshaft sensor feeding the timing referenceCommon
- Damaged crank/cam reluctor rings or tone wheelsCommon
- Damaged, shorted, or open wiring in the signal circuitLess often
- Failed ECM (rare)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and check for companion timing-reference or crank/cam codes.
- Inspect the sensor connector and wiring for damage, corrosion, or looseness.
- Check the reluctor rings/tone wheels for damaged or missing teeth.
- On distributor-based systems, inspect the optical sensor for dirt or wear.
- Replace the high-resolution signal sensor if the pulse count stays low. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0377?+
Not recommended. A missing-pulse timing fault can cause stalling or a no-start, which may leave you stranded. Have it diagnosed first.
Can I just clear P0377?+
It returns as soon as the ECM again counts too few pulses. Repair the sensor, reluctor, or wiring first, then clear and re-test.
Related codes
Often seen with P0377
Read & clear P0377 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX