P0377 — Timing Reference High Resolution Signal “B” Too Few Pulses #

Note: The code description may vary depending on the vehicle manufacturer. Always refer to your OEM (Original Equipment Manufacturer) documentation for the most accurate information.

• P0377: Timing Reference High Resolution Signal “B” Too Few Pulses (Generic/OEM description)
• P0377: CMP Sensor High Resolution Signal “B” Insufficient Pulses (GM, Ford)
• P0377: Camshaft Position Sensor “B” Signal Shortage (Chrysler, Dodge, Jeep)
• P0377: Engine Position Sensor Signal “B” Missing Pulses (Toyota, Lexus)

Summary of Code P0377 #

P0377 is an OBD-II diagnostic trouble code that indicates the powertrain control module (PCM) has detected too few pulses from the high-resolution signal “B” circuit, usually related to a camshaft position sensor or crankshaft position sensor. This signal is crucial for precise engine timing and fuel injection management. The “B” designation typically refers to a secondary sensor or bank 2 sensor, depending on the engine configuration. When this code sets, it means the PCM is not receiving the expected number of timing reference pulses within a given period, which can affect engine performance. Addressing this issue promptly is important to prevent drivability problems and possible engine damage.

Common Symptoms for Code P0377 #

A vehicle with a P0377 code may show a range of symptoms, often related to engine timing and ignition synchronization. Some symptoms can be subtle, while others may be severe enough to affect drivability. Owners may notice the following:

• Check Engine Light illuminated
• Hard starting or no start condition
• Engine misfire or rough running
• Reduced engine power or hesitation
• Poor fuel economy
• Occasional stalling
• Inconsistent or unstable idle speed

Most Likely Causes for Code P0377 #

P0377 can be triggered by several underlying issues. Based on frequency observed in repair shops, these are the most common causes, listed in order of likelihood:

1. Faulty camshaft position sensor (CMP) “B” — The sensor may have failed or is not generating the necessary pulse count.
2. Damaged or corroded wiring/connectors — Wires or connectors in the high-resolution signal “B” circuit may be broken, shorted, or loose.
3. Defective crankshaft position sensor (CKP) — On some engines, the PCM compares cam and crank signals; a bad crank sensor may trigger this code.
4. Timing component issues — Stretched timing chain, worn gears, or a slipped timing belt can cause pulse irregularities.
5. PCM/software fault — Rare, but sometimes the engine control module itself may be at fault or require a software update.

Step-by-Step Diagnostic for Code P0377 #

Diagnosing P0377 requires methodical electrical and mechanical checks. Here’s a recommended process:

• 1. Scan for additional DTCs: Note any related codes (especially cam/crank sensor codes), as they can provide clues.
• 2. Inspect wiring and connectors: Look for damaged, corroded, or loose connections at the CMP “B” sensor and along the harness.
• 3. Test the CMP “B” sensor: Use a digital multimeter or oscilloscope to check sensor output and pulse count during cranking and running.
• 4. Verify sensor power and ground: Ensure the sensor is receiving correct voltage and has a solid ground.
• 5. Check the timing components: If the sensor and wiring are good, inspect the timing chain/belt and related hardware for wear or misalignment.
• 6. Test the CKP sensor (if applicable): Some systems use both sensors for pulse verification.
• 7. Evaluate the PCM: If all else checks out, consider PCM testing or reprogramming as a last resort.

Possible Repairs for Code P0377 #

Repairs for P0377 must address the specific cause found during diagnosis. Here are the most common fixes:

• Replace the camshaft position sensor “B” if it is faulty or not generating the correct signal.
• Repair or replace damaged wiring/connectors in the high-resolution signal “B” circuit.
• Replace the crankshaft position sensor if it is contributing to the signal discrepancy.
• Repair or replace timing components (timing chain, gears, tensioners) if mechanical timing is off.
• Update or reprogram the PCM if a known software issue is identified by the OEM.
• Replace the PCM only if verified defective after all other options are exhausted.

Is It Safe to Drive with Code P0377? #

Limited — Caution Advised: While you may be able to start and drive the vehicle with a P0377 code, it is not recommended. The risk of engine stalling, misfire, poor performance, or even internal damage increases if the underlying issue is not addressed. If you experience hard starting or significant drivability issues, avoid driving until repairs are completed. Always consult your owner’s manual and follow OEM recommendations.

Vehicles Most Commonly Affected by Code P0377 #

While P0377 can appear on many OBD-II equipped vehicles, it is more frequently reported in models with advanced timing control and multiple cam sensors. The following vehicles are known to be more susceptible:

• Chevrolet Silverado, GMC Sierra (2000s–2010s, especially 5.3L/6.0L V8 engines)
• Ford F-Series, Mustang (modular V8 engines with dual cam sensors)
• Dodge Ram, Jeep Grand Cherokee (Hemi and Pentastar engines)
• Toyota Camry, Lexus ES (V6 engines with VVT-i)
• Nissan Altima, Maxima (V6 engines with dual cam sensors)

Common Mistakes & Best Practices for Code P0377 #

Misdiagnosis is common with P0377 due to the complexity of timing and sensor circuits. Follow these tips to avoid wasted time and parts:

• Do not replace sensors without confirming they are faulty—test with a meter or oscilloscope first.
• Always inspect wiring and connectors thoroughly; many issues are due to corrosion, abrasion, or loose pins.
• Don’t overlook mechanical timing—worn timing chains or gears can mimic sensor faults.
• Use only OEM or high-quality aftermarket sensors to avoid repeat failures.
• Clear all codes and perform a drive cycle after repairs to confirm the fix.

Express FAQ for Code P0377 #

Here are answers to some of the most common quick questions about P0377:

Q: Can a low battery or alternator problem cause P0377?
A: Indirectly, yes—voltage irregularities can affect sensor signals. Always verify battery and charging system health during diagnosis.

Q: Is it okay to use universal sensors instead of OEM?
A: For best results, always use sensors matching OEM specifications. Universal sensors may not provide the required resolution and can cause repeat failures or intermittent issues.