Code
P1377
CADILLAC
P — Powertrain
IC Module CAM Pulse To 4X Reference Pulse Comparison
AI status
Completed
Completed
100%
Causes
- Faulty camshaft position sensor (CMP)
- Faulty crank/4X reference sensor or reluctor
- Damaged or corroded sensor connectors or wiring (open, short to ground, short to Vb)
- Intermittent connector or poor ground at IC, PCM or sensor
- Timing chain/belt jumped, stretched, or damaged timing components (phasers, gears)
- Reluctor wheel damage or timing signal tooth missing
Symptoms
- MIL / Check Engine Light on
- Hard starting or no-start condition (intermittent)
- Rough idle, hesitation or misfire
- Loss of power or reduced drivability
- Stored and possibly recurring P1377 and related timing/correlation codes
What to check
- Read freeze frame and related DTCs; note conditions (RPM, temp, battery voltage)
- Visually inspect CMP and crank/4X sensor connectors for corrosion, bent pins, or water intrusion
- Check battery voltage and charging system; ensure good supply during crank
- Perform wiggle test on sensor wiring and connectors while monitoring signals or scan tool
- Check for loose or bad grounds at engine, IC and PCM
- Inspect timing covers/chain/belt condition and tension (if accessible)
Signal parameters
- Camshaft sensor (Hall-type) expected: 0–5 V square wave; clean transitions with consistent amplitude and timing relative to crank
- Crank/4X reference may be Hall or VR type: Hall ~0–5 V square; VR produces AC pulse (amplitude varies with speed, often 0.5–20 VAC peak at higher RPM)
- Signal frequency and pulse spacing increase with RPM; cam pulse usually aligns to a specific crank pulse (cam event once every two crank revolutions)
- Expected: consistent pulse-to-pulse amplitude, stable duty cycle and correct phase relationship between cam and 4X reference at idle and under cranking
Diagnostic algorithm
- Retrieve all stored codes and freeze-frame data. Identify whether related cam/crank correlation codes are present.
- Verify battery voltage ≥ 12 V with key on and during crank. Recharge or replace if low.
- Visually inspect CMP and 4X sensor connectors, harness routing, and grounds. Repair any damage or corrosion.
- Backprobe sensor power, ground and signal circuits. Confirm reference power (if used) and solid ground.
- Capture both cam and 4X reference signals with an oscilloscope while cranking and at idle. Compare waveforms for missing pulses, noise, weak amplitude, or incorrect phase.
- If one sensor signal is missing or noisy, test/replace the suspect sensor. If both signals present but phase is off, check mechanical timing: rotate engine to TDC and verify cam/crank alignment marks.
- Inspect timing chain/belt, phasers, sprockets and tensioners for wear, slack, or jump. Repair or replace timing components if mechanical misalignment found.
- Repair wiring or connector faults. After repairs, clear codes and perform a road test and re-check for recurrence.
- If signals and mechanical timing are correct but code persists, evaluate IC/PCM inputs and consider module replacement only after exhaustive wiring and sensor verification.
Likely causes
- Camshaft position sensor fault or connector/wiring fault
- Crank/4X reference sensor or reluctor damage
- Mechanical timing jumped or phaser failed
- Intermittent wiring/ground issue affecting pulse integrity
Fault status
Status
IC Module detected invalid/incorrect correlation between camshaft pulse and 4X crank/reference pulse — timing/correlation fault.
Repair difficulty: Medium
Diagnostic time: 1.5-3.0 hours
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