On Acura (particularly models with Honda K-series engines like the RSX, TL, TSX), the P1391 code indicates an inconsistency between the signals from the crankshaft position sensor (CKP) and the camshaft position sensor (CMP). This fault disrupts the management of timing and injection.
Common Causes on Acura
- Faulty CKP/CMP Sensors:
- Wear or contamination by oil/metal (common on K20/K24 engines).
- Oxidized connectors (especially in humid climates).
- Timing Issues:
- Slack timing chain (models without a belt).
- Stuck VTC (Variable Timing Control) sprockets (carbon deposits).
- Mechanical Components:
- Damaged crankshaft reluctor wheel (cracks, deformation).
- Oil pump problem (insufficient pressure affecting VTC).
- Electrical Failures:
- Rubbed or cut wiring near the engine block.
- Poor connection at the PGM-FI relay (injection system).
Typical Symptoms on Acura
- 🚨 Persistent “Check Engine” light.
- 🔧 Misfires at idle (especially on Acura RSX Type-S).
- 🌀 Loss of power and hesitant acceleration.
- ⚠️ Hard starting (abnormal knocking).
- ⚡ Excessive fuel consumption.
Acura-Specific Diagnostic
- Advanced OBD-II Scanner:
- Check live data: CKP/CMP deviation > 5°.
- Look for associated codes (P0341, P0339).
- Visual Inspection:
- Inspect CKP/CMP sensors (located on the driver’s side near the flywheel).
- Check the VTC sprocket tightness (access via timing cover).
- Key Tests:
- CKP/CMP resistance: 450–700 Ω (out of tolerance = faulty).
- Oscilloscope signal: Missing peak = damaged reluctor wheel.
- Oil Pressure:
- Measure with a pressure gauge (target: > 35 psi at idle).
Common Repairs
| Cause | Solution | Average Cost |
|---|---|---|
| Faulty CKP sensor | Replace (OEM: Honda 37870-PRB-A01) | 80–150€ + labor |
| Faulty CMP sensor | Cleaning or replacement | 70–130€ |
| Loose timing chain | Replace chain + tensioner | 600–900€ |
| Stuck VTC sprocket | Disassembly/cleaning or replacement | 200–500€ |
| Damaged reluctor wheel | Replace flywheel (extreme case) | 400–800€ |
Common Cases by Model
- Acura RSX (2002–2006):
P1391 often related to the CKP sensor or a VTC misalignment after timing service. - Acura TL (3G, 2004–2008):
Recurring issues with CKP wiring chewed by rodents or oxidized. - Acura TSX (2004–2008):
Code triggered by a worn oil pump → insufficient pressure for VTC.
Acura Technical Tips
- ⚠️ Do not ignore the code: Risk of unexpected stalling or VTC damage.
- Post-repair reset:
- Clear the code with a scanner + idle learn procedure (10 min with warm engine).
- Use OEM parts:
- Generic sensors often cause recurring issues on Acura.
In Summary
P1391 on Acura generally points to:
🔧 1 faulty CKP/CMP sensor (50% of cases)
⚙️ 2 a timing/VTC issue (30% of cases)
🔌 3 an electrical problem (20% of cases).
A thorough inspection of the timing system and electrical signals is crucial. If the fault persists after replacing sensors, check the ECU power supply voltage and engine ground. Consult an Acura specialist for a precise diagnosis if necessary.