Your 7th Gen (EM2/ES1), 8th Gen (FA5/FG2), 9th Gen (FB6/FG4), 10th Gen (FC1/FK7), or 11th Gen (FL1/FL5) Civic just threw a P0340 — and the ECU cannot detect the Camshaft position.
P0340 is the code for “Camshaft Position Sensor ‘A’ Circuit Malfunction”. The ECU is indicating that it cannot read the intake camshaft (Sensor A is always the intake cam on Hondas). Unlike crank sensor codes (P0335/P0336) that typically prevent the engine from starting, P0340 usually allows the vehicle to start and run — but it may operate in a limited-performance mode.
Here is a garage-tested breakdown of what P0340 actually means on these cars, and how to repair it without unnecessary expense AT the dealership.
P0340 Breakdown: Understanding the Camshaft Signal Loss
P0340 (“Camshaft Position Sensor Circuit Malfunction”) indicates that the ECU is not receiving a valid signal from the intake Camshaft Position Sensor.
The camshaft position sensor (CMP) provides the ECU with the precise position of the intake cam in its rotation. The ECU uses this information to time fuel injectors and, on VTEC engines, to engage the high-lobe cam profile. When the ECU loses the cam signal, it may enter a limited-performance mode — retarding timing, disabling VTEC, and limiting RPM.
The Symptoms:
- Hard start / extended crank — the engine cranks longer than normal before starting
- VTEC disabled — reduced performance above 4,000 RPM
- Loss of power — sluggish acceleration
- Rough idle — the engine may stumble or surge
- Multiple warning lights — CEL, VSA, and Traction Control may illuminate
- Cold start timing chain rattle — on K-series, a brief rattling sound on startup (indicative of VTC actuator wear)
Key Considerations: The “Fake” Sensor Code
An important diagnostic consideration: In the majority of P0340 cases on Hondas, the CMP sensor itself is not the issue.
1. Timing Chain Stretch.
When the Timing Chain stretches on a Honda (particularly the K-series and L15B7), the camshaft and crankshaft become out of sync. The ECU detects the mismatch between the CKP and CMP signals and sets P0340. This is typically a mechanical issue — not a faulty sensor.
Diagnostic clue: If the code appears alongside P0336 or P0339 (crank sensor codes), Timing Chain Stretch is likely. The ECU is detecting that the cam and crank are no longer synchronized.
2. VTC Actuator Wear (K-series Cold Start).
On 8th and 9th Gen Si (K20Z3 / K24Z7), the VTC actuator (cam phaser) is a known wear item. When the actuator’s internal locking pin wears, a brief rattling sound on cold start may occur. The camshaft may move erratically during startup, and the ECU may see inconsistent cam timing, setting P0340.
3. VTEC Solenoid / Oil Pressure Issues.
The VTC system operates on engine oil pressure. If the oil level is low, the oil is dirty, or the VTEC solenoid screen is clogged, the VTC actuator may not move the cam properly. The ECU may detect the cam in the wrong position and set P0340.
Diagnostic tip: Check the oil level before replacing any components. Low oil is a common cause of P0340 on Honda VTC systems.
4. Oil in the Connector (Valve Cover Leak).
On R18 engines, the camshaft position sensor is located on top of the cylinder head. Over time, the valve cover grommet around the sensor can harden and leak. Engine oil may enter the sensor connector, causing signal issues and setting P0340.
Generation & Engine Specifics
8th & 9th Gen Si (K20Z3 / K24Z7):
- ⚠️ The VTC Actuator Rattle. On cold starts, a loud rattle for 1-2 seconds followed by P0340 typically indicates the VTC actuator (cam phaser) is failing. The internal locking pin is worn.
- The Fix: Replace the VTC actuator. This is a $150–$280 part (OEM) and requires timing Chain removal. If replacing the VTC actuator, replace the timing chain and tensioner at the same time — the components are already accessible.
- Sensor location: On the front of the cylinder head, near the VTEC solenoid.
- Part number: 14310-R40-A01 (VTC actuator for K20Z3).
8th & 9th Gen Base Models (R18 / 1.8L):
- ⚠️ The Valve Cover Grommet Leak. The CMP sensor is mounted on top of the Valve Cover. When the rubber grommet hardens, oil can leak into the connector, causing signal issues.
- The Fix: Unplug the sensor, clean the connector with brake cleaner, dry it, and reinstall. If the code returns, replace the valve cover Gasket set ($25–$45).
- Sensor location: On top of the valve cover, near the timing chain cover.
10th & 11th Gen 1.5T (L15B7 / Direct Injection):
- ⚠️ Tuned Engine Consideration. On the 1.5T, P0340 is often timing chain stretch on high-mileage vehicles or those with aggressive tunes.
- Important: If running a tune and P0340 is present, do not ignore it. A stretched chain on a boosted L15B7 can jump timing — which may result in valve-to-piston contact and extensive engine damage.
- Check the chain tensioner: Remove the right wheel and the plastic inspection cover. If the tensioner has more than 5-6 mm of plunger travel, the chain is stretched and requires replacement.
- Sensor location: On the front of the cylinder head, near the timing chain cover.
10th & 11th Gen Type R (K20C1, FK8/FL5):
- The K20C1 has similar vulnerabilities to the K20Z3 — VTC actuator wear and timing chain stretch.
- If running heavy boost with an aftermarket tune, P0340 may reduce boost targets and limit performance.
- Fix: Check the VTC actuator first, then the timing chain.
Actionable Diagnostics — Step-by-Step
This diagnostic routine will help you avoid unnecessary parts replacement.
Step 1: The Oil Level and Condition Check.
Check the oil level and condition. Is the oil low? Is it dark and dirty?
The Verdict:
- If the oil is low: Top it up. The VTC system operates on oil pressure. Low oil can prevent the cam from moving to the commanded position.
- If the oil is dirty: Change it. A clogged VTEC solenoid screen can cause cam timing issues.
Step 2: The Connector Check (Oil-in-the-Plug Inspection).
Unplug the CMP sensor (Sensor A — the intake cam sensor, on the front of the head). Inspect the connector interior.
The Verdict:
- If oil is visible in the connector: The valve cover grommet is leaking. Clean the connector with brake cleaner, dry it, and reinstall. If the code returns, replace the valve cover gasket set.
- If the connector is dry: Proceed to Step 3.
Step 3: The Timing Chain Tensioner Check.
Remove the right front wheel and the plastic inspection cover on the timing chain cover. Inspect the timing chain tensioner.
The Verdict:
- If the tensioner has more than 5-6 mm of plunger travel: The chain is stretched and requires replacement. Do not replace the sensor — the chain requires attention.
- If the tensioner is within specification: Proceed to Step 4.
Step 4: The CMP Sensor Replacement (Last Resort).
If the oil is good, the connector is dry, and the timing chain is within specification, the CMP sensor may be faulty. Use OEM Honda, Denso, or Hitachi sensors. Inexpensive aftermarket sensors may not function reliably at high RPM under load.
After replacing the sensor, perform the camshaft position relearn procedure if the scan tool supports it.
Parts, Cost Breakdown & US Sourcing
| Part | Fits | OEM Part Number | Online Cost | Dealer Cost |
|---|---|---|---|---|
| CMP Sensor (Denso) | 8th/9th Gen R18 | Verify by VIN | $40–$65 | $80–$120 |
| CMP Sensor (Hitachi) | 8th/9th Gen K-series | Verify by VIN | $45–$70 | $90–$130 |
| CMP Sensor (Denso) | 10th Gen L15B7 1.5T | Verify by VIN | $50–$80 | $100–$150 |
| VTC Actuator (OEM) | 8th Gen Si K20Z3 | 14310-R40-A01 | $150–$280 | $350–$550 |
| Timing Chain Kit (OEM/Cloyes) | All Generations | Verify by VIN | $130–$250 | $400–$700 |
| Valve Cover Gasket Set | 8th/9th Gen R18 | Verify by VIN | $25–$45 | $60–$100 |
Repair Cost Breakdown
| Repair | DIY Cost | Independent Shop | Honda Dealer |
|---|---|---|---|
| Oil Change + VTEC Screen Clean | $30–$50 | $80–$150 | $120–$200 |
| CMP Sensor Replacement | $40–$80 | $150–$250 | $200–$350 |
| Valve Cover Gasket Replacement (R18) | $25–$45 | $150–$250 | $250–$400 |
| VTC Actuator Replacement (K-series) | $150–$280 | $500–$1,000 | $1,200–$1,800 |
| Timing Chain Replacement | $130–$250 | $900–$1,500 | $2,000+ |
| Dealer Diagnostic Fee | N/A | N/A | $120–$200 |
Sourcing Tip: We track live market rates and cross-reference part numbers directly from US OEM catalogs such as HondaPartsNow and popular distributors like RockAuto and Fitment Industries.
Used Buyer Warning
If you are test-driving a Civic that has a cold start rattle and a P0340 code, proceed with caution.
If the seller claims it just needs a cheap sensor — negotiate accordingly or consider walking away.
Why this matters:
- K-series VTC Rattle: If the cold start rattle is present on an 8th/9th Gen Si, the VTC actuator is likely failing. This is a $500–$1,000 shop repair. If the seller has not addressed it, budget for it.
- Timing Chain Stretch: A stretched chain will not be fixed by replacing the sensor. A $900–$1,500 timing chain service is required. On an L15B7, a stretched chain at elevated boost levels is a significant risk — it can jump timing and cause engine damage.
- Oil Leak: If the seller says “it just needs a sensor,” check the connector for oil. If oil is present, the valve cover gasket is leaking — a $250+ repair.
- If the seller cannot clear the code and demonstrate a smooth idle, consider this a warning sign.
Used buyer rule: P0340 with cold start rattle should be treated with caution — inspect the VTC actuator and timing chain, or have the vehicle evaluated by a professional.
Quick Reference Checklist
☐ P0340 = Camshaft Position Sensor Circuit Malfunction — ECU cannot read the intake cam signal
☐ In the majority of P0340 cases, the sensor is not the issue — timing chain stretch, VTC actuator wear, or low oil are more likely
☐ Check oil level and condition first — low or dirty oil can cause VTC issues
☐ Check the CMP sensor connector for oil — on R18, the valve cover grommet may leak oil into the plug
☐ 8th/9th Gen K-series: Cold start rattle + P0340 = VTC actuator failure — budget for replacement
☐ Check timing chain tensioner — if the plunger has more than 5-6 mm of travel, the chain is stretched
☐ 10th/11th Gen L15B7: P0340 on a tuned vehicle = timing chain stretch — address promptly to avoid timing jump
☐ VTEC solenoid screen — a clogged screen can restrict oil flow to the VTC actuator
☐ Avoid low-cost sensors — they may fail at high RPM under load
☐ Use OEM Honda, Denso, or Hitachi — these are the only sensors that provide reliable operation
☐ Used Buyer Rule — P0340 with cold start rattle on K-Series indicates VTC actuator wear; on L15B7, timing chain stretch. Do not purchase without proper inspection.