The P1390 code on Chevrolet vehicles (Silverado, Tahoe, Malibu, Equinox, etc.) indicates a critical desynchronization between the crankshaft (CKP) and the camshaft (CMP), preventing the ECU from controlling ignition and injection. Without prompt intervention, this fault can lead to serious engine damage.
🚨 Immediate Symptoms
- Engine hard to start or sudden stalling.
- Severe misfires and loss of power during acceleration.
- Check engine light on (sometimes flashing) + associated codes (P0016, P0340).
- Metallic noises near the timing cover (chain/timing gear).
🔧 Specific Chevrolet Causes
- Stretched timing chain (common on GM V6/V8 engines > 120,000 km).
- Failed hydraulic chain tensioner (oil leak or mechanical blockage).
- Dirty/defective CKP or CMP sensors (exposed to oil leaks).
- Damaged reluctor wheel (missing teeth or demagnetized magnet).
- Insufficient oil pressure (worn pump, degraded oil, clogged filter).
🔍 Step-by-Step Diagnosis
- Check oil pressure:
- Minimum 15 psi at idle, ideal 35–60 psi at 2,000 rpm (use ACDelco T-80 gauge).
- Inspect the timing chain:
- Access via side cover (models Silverado, Tahoe, Malibu 2.4L).
- Check lateral play (max 6 mm) and alignment marks.
- Test sensors:
- CKP: Resistance 850–1350 Ω (typical value V6 3.6L).
- CMP: AC 0.3–3V signal on oscilloscope.
- Advanced GM scan:
- Use Tech2 or GDS2 to compare CKP/CMP signals (offset > 2° = confirmed fault).
🛠️ Recommended Repairs (With OEM References)
| Faulty Component | Solution | ACDelco/GM Parts |
|---|---|---|
| Timing chain | Replace complete kit (chain + tensioners + guides) | GM 12640486 (V8 5.3L) / 12633846 (V6 3.6L) |
| Hydraulic tensioner | Replace + check oil supply | ACDelco 12633825 |
| CKP sensor | Replace (air gap: 1.0 ± 0.5 mm) | ACDelco 213-1151 (Silverado) |
| CMP sensor | Clean or replace | Delphi FG1105 (Equinox) |
| Reluctor wheel | Inspect crankshaft rotor (bent/missing teeth) | GM 12586459 |
⚠️ Critical Warning:
On Chevrolet interference engines (Ecotec, V8 Vortec), desynchronization causes piston-valve collision. Stop the engine at the first abnormal noises!
💡 Key Post-Repair Procedures
- Timing alignment:
- Use GM tools J-42386 (crankshaft lock) and J-45027 (camshaft locks).
- ECU reset:
- Clear code with Tech2/GDS2 + perform a timing relearn.
- Oil control:
- Use a 5W-30 Dexos1 (e.g., Mobil 1 ESP) + GM filter PF64.
📊 Technical Sheet
| Parameter | Value |
|---|---|
| OBD2 Code | P1390 |
| Definition | CKP/CMP correlation error |
| At-Risk Models | Silverado, Tahoe, Equinox, Malibu (2004–2018) |
| Urgency | MAXIMUM (risk of engine failure) |
Comparison of Common Causes by Model
| Model | Recurring Problem | Typical Solution |
|---|---|---|
| Silverado 5.3L | Failed hydraulic chain tensioner | Replace GM chain kit 12640486 |
| Equinox 2.4L | Oxidized reluctor wheel | Change crankshaft rotor GM 12586459 |
| Malibu 3.6L | CMP sensor flooded with oil | Replace + seal Delphi FG1105 |
Conclusion
The P1390 code on Chevrolet indicates a potentially destructive engine synchronization fault. Major causes include:
- Timing chain wear (especially on high-mileage V6/V8 engines),
- CKP/CMP sensor failure (aggravated by oil leaks),
- Insufficient oil pressure.
Recommended procedure:
- Start by checking oil pressure and timing condition.
- Replace faulty components with ACDelco/GM parts.
- Perform precise timing alignment with dedicated tools and reset the ECU.
Do not drive with this code – have the vehicle towed to a GM-certified technician equipped with a Tech2/GDS2 scanner to avoid costly repairs (e.g., engine replacement).