Introduction
The error code P1390 is specific to Honda and Acura vehicles. It indicates an anomaly in the camshaft position circuit (Bank 1), related to the VTEC system (Variable Valve Timing and Lift Electronic Control). This system optimizes engine performance and efficiency by adjusting valve timing. Ignoring this code can lead to power loss, increased fuel consumption, or engine damage.
VTEC Operation: Technical Overview
The VTEC system uses pressurized engine oil to activate a mechanism that changes the camshaft profile:
- At low RPM: “Mild” profile for fuel economy.
- At high RPM: “Aggressive” profile to increase power.
The P1390 code occurs when the PCM (Powertrain Control Module) detects an abnormal discrepancy between the signals from the camshaft position sensor (CMP) and the crankshaft position sensor (CKP).
Possible Causes of P1390
- Engine Oil Issues:
- Low oil level.
- Degraded oil or incorrect viscosity (e.g., not using 5W-30).
- Clogged oil filter or VTEC filter (due to deposit buildup).
- Electrical Failures:
- Faulty VTEC solenoid (most common).
- Failed camshaft position sensor (CMP).
- Damaged wiring (short circuits, corrosion).
- Mechanical Problems:
- Weak oil pump (insufficient pressure).
- Worn or stuck VTEC gears.
- Internal oil leaks in the VTEC mechanism.
- PCM Errors (rare):
- Software or hardware failure of the control module.
Common Symptoms
- 🚨 Check Engine light illuminated.
- 🐌 Power loss (especially at high RPM).
- 🔉 Clicking or abnormal noises from the engine.
- ⛽ Increased fuel consumption.
- ⚠️ Unstable idle or stalling.
Step-by-Step Diagnosis
- Check Engine Oil:
- Inspect level and quality. Replace if necessary with recommended oil (e.g., 5W-30).
- Scan for Related Codes:
- Look for associated codes (e.g., P0341, P2646) to refine diagnosis.
- Inspect VTEC Solenoid:
- Electrical Test: Measure resistance (normal range: 14–30 Ω).
- Functional Test: Apply 12V to check for a “click” sound.
- Clean VTEC Filter (located under the solenoid).
- Check Oil Pressure:
- Use a pressure gauge (target: 40–80 psi at 3,000 RPM).
- Inspect Sensors and Wiring:
- Check CMP and solenoid connectors. Test wire continuity.
- Analyze Live Data:
- Observe CMP/CKP signals with an oscilloscope (look for discrepancies).
Repair Solutions
| Cause | Solution | Estimated Cost |
|---|---|---|
| Low/degraded oil | Oil change + oil filter. | 50–100 € |
| Faulty VTEC solenoid | Replace solenoid (OEM: 31110-PAA-003). | 80–200 € (part) |
| Clogged VTEC filter | Clean or replace. | 5–20 € |
| Faulty CMP sensor | Replace sensor. | 60–150 € |
| Weak oil pump | Replace pump (requires engine disassembly). | 400–800 € |
| Damaged wiring | Repair wires or replace harness. | 50–300 € |
Common Mistakes to Avoid
- Neglecting the VTEC filter (small but critical!).
- Using non-compliant oil not meeting Honda specifications.
- Forgetting to reset the PCM after repair (via OBD2 scanner).
Conclusion
The P1390 code is often related to neglected maintenance (oil or filters). Start with simple checks (oil level, VTEC filter) before exploring complex causes (oil pump, PCM). Prompt action prevents costly damage to the VTEC system. If diagnostic steps exceed your skills, consult a Honda/Acura specialist mechanic.
Tip: Perform regular oil changes with quality oil to prevent 70% of P1390 occurrences!