1. Meaning of GMC Code P1392
P1392 on GMC vehicles indicates an intermittent inconsistency between the crankshaft position (CKP) and camshaft position (CMP) sensors. This fault disrupts engine timing and can affect:
- Variable Valve Timing (VVT)
- The Active Fuel Management (AFM/DOD) system
- Performance and fuel consumption
2. Affected GMC Models
| Model | Engine | Years | Typical Mileage |
|---|---|---|---|
| Sierra 1500 | 5.3L V8 (L84) | 2019-2023 | 80,000-130,000 km |
| Acadia | 3.6L V6 (LGX) | 2017-2023 | 60,000-100,000 km |
| Canyon | 2.8L Diesel (LWN) | 2015-2023 | 70,000-120,000 km |
| Yukon | 6.2L V8 (L87) | 2021-2023 | 50,000-80,000 km |
3. Main Causes
A. Mechanical Problems (45%)
- Stretched timing chain (especially 5.3L/6.2L)
- Worn tensioner or guides
- Variable phasing (VVT) issue
B. Electrical Failures (35%)
- Faulty CMP sensor (often on passenger side)
- Connector problem (corrosion on C101/C105)
- Damaged wiring near exhaust
C. Other Causes (20%)
- Insufficient/degraded engine oil
- Low oil pressure
- Outdated ECM software
4. Step-by-Step Diagnosis
Step 1: Initial Checks
- Check oil level and quality
- Visually inspect sensor connectors
- Check for related fault codes (P0016, P0340, etc.)
Step 2: Electrical Tests
- CMP resistance: 750-1500Ω (varies by model)
- CKP signal: 0.5-3V AC during startup
- Wire continuity (resistance <1Ω)
Step 3: Mechanical Check
- Timing mark alignment
- Chain slack (GM special tool J-45027 recommended)
- Condition of tensioners and guides
5. Recommended Solutions
For 5.3L/6.2L V8:
- Complete timing chain kit replacement (including new tensioners)
- ECM software update (TSB 18-NA-355)
- Cleaning AFM solenoids
For 3.6L V6:
- CMP sensor replacement (P/N 12677925)
- Timing actuator inspection
- Oil change with Dexos2 oil
For 2.8L Diesel:
- Oil pump check
- CMP/CKP sensor inspection (shielded version)
6. Key Technical Data
- Minimum oil pressure: 25 psi (hot idle)
- Timing tolerance: ±5°
- Chain interval: 150,000 km (but often at 100,000 km)
7. Estimated Costs
| Service | Cost (CAD) | Warranty |
|---|---|---|
| Sensor replacement | $200-400 | 2 years |
| Complete chain kit | $1,500-3,000 | 1 year |
| Reprogramming | $100-250 | 90 days |
8. Mistakes to Avoid
- Using non-OEM parts (high failure rate)
- Neglecting software updates
- Forgetting to reset adaptations after repair
9. FAQ
Q: Can I drive with this code?
→ No, risk of severe engine damage (especially with AFM)
Q: Why more frequent on recent GMCs?
→ Combination of thinner chains and complex VVT systems
Q: How to prevent this issue?
- Regular oil changes (every 5,000 km under severe use)
- Exclusive use of Dexos2 oil
- Annual inspections from 80,000 km
10. Conclusion
Code P1392 on GMC requires prompt attention:
- Complete diagnosis with GM MDI tool
- Thorough mechanical inspection
- Use of genuine GM parts
⚠️ Important warning: Engines with AFM can suffer catastrophic damage if this code is ignored. Consult a certified GMC technician as soon as the check engine light appears.