P0377: Timing Reference High Resolution Signal B Too Few Pulses
The PCM has detected that the high resolution timing reference signal from the crankshaft position sensor (CKP) or camshaft position sensor (CMP) has fewer pulses than expected. This signal is critical for engine timing, fuel injection, and ignition synchronization. A low pulse count indicates a weak or intermittent signal, often due to sensor degradation, wiring issues, or a damaged reluctor wheel.
01. Most Common Causes
- Faulty crankshaft or camshaft position sensor
- Damaged or contaminated reluctor wheel
- Wiring or connector issues (shorts, opens, corrosion)
- Intermittent electrical connection
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Engine misfire or rough idle
- Hard starting or no start
- Reduced engine performance
03. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data.
Step 2: Visually inspect CKP/CMP sensor wiring and connectors for damage or corrosion.
Step 3: Test sensor resistance and AC voltage output while cranking using a multimeter.
Step 4: Inspect reluctor wheel for damage, debris, or excessive runout.
Step 5: Replace sensor if signal is weak or absent; clear codes and test drive.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
No, it is not safe. The engine may stall or fail to start, and driving could cause further damage to the catalytic converter or other components.
How much does it cost to fix?▼
Typically $50-$150 for a sensor replacement, plus diagnostic time. Costs vary by vehicle and shop labor rates.