The P1390 code on Cadillac indicates a critical desynchronization between the crankshaft (CKP) and camshaft (CMP), risking severe engine damage. Common on Northstar V8 and LFX engines, this fault requires prompt intervention.
🚨 Immediate Symptoms
- Failure to start or sudden engine shutdown.
- Metallic rattling near the timing case (loose chain).
- Sudden power loss + red engine warning light.
- Misfires (associated codes P0300-P0308).
🔧 Specific Cadillac Causes
- Stretched timing chain (premature wear on Northstar V8 > 150,000 km).
- Failed chain tensioner (hydraulic system blocked or leaking).
- Dirty or faulty CKP/CMP sensors (exposure to oil leaks).
- Damaged tone wheel (missing teeth or demagnetized magnet).
- Engine oil issue: low level, incorrect viscosity, or weak pump.
🔍 Step-by-Step Diagnosis (High Priority)
- Check oil pressure:
- Minimum required: 20 psi at idle (use Kent-Moore J-21867 gauge).
- Target: 40–60 psi at 2,000 RPM.
- Inspect timing chain:
- Access via side cover (on CTS, STS, Escalade models).
- Check lateral play (max 5 mm) and alignment marks.
- Test sensors:
- CKP: Resistance 900–1100 Ω (ACDelco 12638548).
- CMP: Signal voltage 0.3–5V while rotating (oscilloscope tool).
- Advanced GM scan:
- Compare CKP/CMP signals via Tech2 or GDS2 (offset > 3° = confirmed fault).
🛠️ Validated Repairs (With References)
| Faulty Component | Solution | Recommended OEM Parts |
|---|---|---|
| Timing chain | Replace full kit (chains + tensioners + guides) | GM 12640485 (Northstar V8 Kit) |
| Hydraulic tensioner | Replace + check oil circuit | ACDelco 12633825 |
| CKP/CMP sensor | Clean or replace (air gap: 0.5–1.5 mm) | Delphi FG1022 (CKP), FG1105 (CMP) |
| Tone wheel | Replace crankshaft rotor | GM 12586459 |
⚠️ Critical Warning:
On interference engine Cadillacs (e.g., Northstar), desynchronization can cause piston-valve collision. Stop the engine immediately if abnormal noises occur!
💡 Key Procedures
- Use GM timing tools:
- J-42386 (crankshaft lock) + J-42387 (camshaft locks) for Northstar.
- Post-repair check:
- Reset ECU with Tech2, then perform a timing relearn.
- Engine oil: Exclusively 5W-30 Dexos1 (e.g., Mobil 1 ESP).
📊 Technical Sheet
| Code | P1390 |
|---|---|
| Definition | CKP/CMP correlation error |
| At-Risk Models | CTS, STS, SRX, Escalade (2000–2015) |
| Urgency | MAXIMUM (risk of engine destruction) |
Conclusion
The P1390 code on Cadillac reveals a potentially catastrophic engine synchronization fault. Major causes include timing chain wear, faulty sensors, or insufficient oil pressure. Immediate action is crucial:
- Check oil pressure and timing system condition.
- Replace faulty components with GM/ACDelco parts.
- Perform precise timing with dedicated tools.
Do not attempt this repair without expertise – consult a GM-certified technician equipped with a Tech2/GDS2 scanner to avoid major repair costs.