P1377

Code

CHEVROLET P — Powertrain

IC Module CAM Pulse To 4X Reference Pulse Comparison

Brand: CHEVROLET

Type: P — Powertrain

Views: UK: 30 EN: 41 RU: 33

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Page language: EN

Causes

Faulty or intermittent camshaft position sensor
Faulty or intermittent crankshaft/4X reference sensor or damaged reluctor/toner wheel
Damaged wiring, broken wires, poor connector contacts, or corrosion in sensor circuits
Timing chain/belt jump, stretched chain, or incorrect mechanical timing after service
VVT (variable valve timing) actuator or oil control valve failure causing cam timing drift
Faulty PCM/Integrated Control (IC) module or internal comparator fault

Symptoms

Malfunction Indicator Lamp (MIL) illuminated
Hard start, extended crank, or no‑start condition
Rough idle, misfire, or intermittent stalling
Reduced engine power or poor drivability
Stored misfire or cam/crank correlation related codes

What to check

Read stored codes and freeze frame data; confirm P1377 and any related codes (cam/crank, misfire, battery/charging).
Capture live data: camshaft position, crankshaft/4X reference counts and timing; verify cam vs crank correlation at idle and during crank.
Perform an oscilloscope capture of cam sensor and 4X reference/crank sensor signals simultaneously to verify waveform timing and integrity.
Visually inspect sensor connectors, wiring harness for chafing, corrosion, pin damage or loose terminals; wiggle test while monitoring data/waveforms.
Inspect reluctor/toner wheel or target ring for damaged/missing teeth or debris and check sensor air gap and mounting.
Check battery voltage and engine grounds; verify stable supply and reference voltages to sensors while cranking and running.

Signal parameters

Camshaft position sensor: typically produces one pulse per camshaft cycle (varies by engine); pulse timing relative to crank is critical.
4X crank reference: provides multiple evenly spaced reference pulses used for synchronization on some GM engines (verify exact pulse count for the engine).
Hall‑type sensors: near 0–5 V square wave. Logical high typically ~5 V, low ~0 V.
Variable reluctance (VR) sensors: AC sine waveform; amplitude rises with engine speed (often ~0.2–2 VAC at cranking, higher at speed).
Expected correlation: cam pulse position should occur at a defined angle relative to the 4X crank pulses. Any large phase shift, missing pulses, or jitter indicates a problem.

Diagnostic algorithm

Confirm the code and note freeze frame / engine conditions when the code set.
Check battery voltage and engine grounds; repair poor connections and retest.
Visually inspect cam and crank sensor connectors and wiring. Repair any damage and clear codes.
Use a scan tool to monitor cam and crank/4X signals (or counts) while cranking and running; look for missing or unstable pulses.
If available, capture both sensor waveforms with an oscilloscope to verify timing relationship and signal quality (check amplitude, shape, and timing).
If signal quality is poor on one sensor, test the sensor per manufacturer procedure (voltage, resistance, AC output for VR sensors) and replace if out of spec.
If signals are good electrically but correlation is out of tolerance, inspect the reluctor/toner wheel and timing components for damage or timing jump; verify mechanical timing marks.
Check VVT actuator/solenoid operation and oil control (low oil pressure or stuck actuator can alter cam timing).
After repairs, clear codes and perform a road test or drive cycle to confirm code does not return; recheck waveform/correlation under load and at various RPMs.
If all sensors, wiring, and mechanical timing check good and the code persists, consider PCM/IC module fault and consult manufacturer resources for module bench tests or reprogramming.

Likely causes

Wiring/connectors between cam sensor and IC module (most common)
Failed camshaft position sensor
Failed crankshaft/4X reference sensor or damaged reluctor ring
Timing chain/belt jumped or mechanical timing error
VVT actuator or oil control valve causing incorrect cam timing
PCM/IC module fault (less common)

Fault status

⚠️ Status

PCM/IC module detected camshaft pulse does not match expected timing relationship to the 4X crank reference pulse; cam/crank correlation out of tolerance.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.5 - 4.0 hours

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