Code
P1377
GMC
P — Powertrain
IC Module CAM Pulse To 4X Reference Pulse Comparison
AI status
Completed
Completed
100%
Causes
- Failed or intermittent camshaft position sensor (CMP)
- Failed or intermittent crankshaft position sensor (CKP) / 4X reference sensor
- Damaged or corroded wiring, connectors, or poor grounds for cam/crank/IC module
- Incorrect cam/crank timing (timing chain/belt jumped or damaged reluctor)
- Reluctor wheel damage or missing teeth on crank/cam tone wheel
- Intermittent power supply to sensors or IC/module
Symptoms
- Malfunction Indicator Lamp (MIL) / Check Engine light illuminated
- Hard start or no-start condition
- Rough idle, hesitation, or engine misfire
- Reduced engine power or limp-home mode
- Intermittent stalling or poor driveability
- Stored or pending misfire codes or other cam/crank correlation DTCs
What to check
- Retrieve freeze frame and all stored codes; note conditions when fault set
- Verify battery voltage and charging system health
- Visual inspection of cam and crank sensor connectors, wiring harness, and grounds
- Check for physical damage or missing teeth on tone/reluctor wheels
- Wiggle test wiring/connectors while monitoring live data for dropouts
- Compare cam and crank signals with an oscilloscope while cranking/running
Signal parameters
- Cam sensor type: Hall or variable reluctance (confirm vehicle-specific type)
- Hall sensor waveform: digital 0–5 V square wave; clean transitions and correct duty
- Variable reluctance waveform: AC voltage amplitude varies with rpm (millivolts to volts)
- 4X reference: expected frequency proportional to engine rpm; pulses per crank revolution depends on design (verify OEM spec)
- Expected phasing: cam pulse should correlate to crank 4X reference per OEM timing relationship
- Look for missing pulses, shifted phase, excessive jitter, or amplitude dropouts
Diagnostic algorithm
- Record codes and freeze-frame data; clear codes and attempt to re-create fault.
- Verify vehicle battery is fully charged and system voltage stable during cranking.
- Perform visual inspection: connectors, pins, corrosion, chafing, or crushed wires for cam, crank, and IC module.
- Back-probe sensor power, ground and signal circuits; verify proper supply voltage and ground continuity.
- Use an oscilloscope to capture cam and crank (4X) waveforms simultaneously while cranking and at idle; compare phase, amplitude and pulse count to OEM reference.
- If waveforms show missing or noisy signals, isolate by substituting a known-good sensor (if available) or repairing wiring/connector faults.
- If signals are present but out of phase, inspect timing components (timing chain/belt, tensioner, sprockets, reluctor wheel) for jumped timing or damage.
- Repair/replace faulty sensor, repair wiring/connector issues, or correct mechanical timing as required.
- After repairs, clear codes and road-test; recheck for code recurrence and verify proper waveform correlation.
- If electrical and mechanical checks are good but code persists, consider IC module/PCM testing or replacement and check for software updates/TSBs.
Likely causes
- Faulty camshaft position sensor or connector
- Damaged wiring or poor ground between sensors and module
- Crank 4X reference sensor fault or damaged reluctor wheel
- Timing chain/belt jumped resulting in cam/crank correlation error
- Intermittent module failure or software issue
Fault status
Status
IC module detected mismatch between camshaft pulse and 4X crank reference pulse (cam/crank correlation fault).
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email