P0340 Code: Honda Accord (2018-2023) - Causes, Symptoms & Fixes

Comprehensive diagnostic guide for OBD-II code P0340 on 2018-2023 Honda Accord

Important data note

• Real NHTSA data provided: No complaints found for this make/model/year/issue combination.
• Recalls: No recalls found in NHTSA database for this make/model/year.
• How this affects guidance: The guide leans on general OBD-II diagnostics and Honda-specific tendencies for P0340, since the provided data contains no complaints or recalls. If you have a dealer bulletin or TSB, it’s not included here due to data limits. Always verify against current factory resources if you have access.

CODE MEANING AND SEVERITY

• What P0340 means: Camshaft Position Sensor Circuit Malfunction (CMP sensor circuit). The PCM detects an incorrect or unavailable camshaft position signal.
• Why it matters: The CMP signal is used to time spark and sequential fuel injection. A faulty signal can cause mis-timing, misfires, reduced power, stalling, or no-start conditions.
• Severity on a 2018-2023 Honda Accord: Can range from a limp-mode condition with reduced power (and check engine light) to a no-start situation. In some cases the engine may run inconsistently or stall. If the signal is intermittent, symptoms may come and go.

COMMON CAUSES ON HONDA ACCORD

Note: Honda CMP (camshaft position sensor) logic is sensitive to wiring and timing. Causes commonly seen on Accords in this generation include:

• Faulty camshaft position sensor (CMP) itself (aged sensor, internal wiring failure, poor reliability).
• Damaged or corroded CMP sensor wiring harness or connectors (pin damage, loose connector, water/oil intrusion).
• Open or short in the CMP signal or reference/ground circuits (faulty insulation, chafed wires, poor ground).
• Electrical interference or a poor PCM input due to a related sensor issue (rare, but possible): especially if the vehicle also shows P0010/P0011 (VVT solenoid or cam timing control issues) or P0335 (crankshaft position sensor).
• Timing-related problems: timing chain/belt slippage or stretched chain, mis-timed camshaft, or a faulty timing tensioner/guide that alters the cam timing enough to affect the CMP signal interpretation.
• Variable Valve Timing Control (VTC) system issues on engines with VTC: stuck or sluggish valve timing components can affect cam timing signals.
• Oil contamination or excessive sludge around the sensor area or reluctor wheel (less common but possible with poor maintenance).

SYMPTOMS YOU MIGHT SEE

• Check Engine Light (CEL) or MIL illuminated.
• Engine starts hard or fails to start; idle may be rough or unstable.
• Power loss, hesitation, or reduced acceleration.
• Intermittent stalling or misfires (P0300-type behavior may accompany P0340).
• Inconsistent engine performance across RPMs; running quality improves or deteriorates intermittently.
• No obvious mechanical noises specifically tied to P0340, but timing-related issues can manifest as mis-timing symptoms.

DIAGNOSTIC STEPS (step-by-step, practical workflow)

Note: This is a structured approach. Start with electrical checks, then mechanical validation if needed.

A. Verify the code and data

• Use a reliable OBD-II scanner with live data. Confirm P0340 and note any related codes (P0341, P0342, P0343, P0335, P0336, P0010, P0011, etc.).
• Check freeze-frame data: engine RPM, coolant temp, load, and any spark/fuel-related data at the time the code was stored.
• Check for misfire codes (P0300-P0304) that could accompany a CMP fault.

B. Visual inspection

• Inspect CMP sensor and wiring connector for signs of damage, oil/water intrusion, corrosion, or broken pins.
• Check the wiring harness routing near the timing cover, water pump area, and along the valve cover for chafing, abrasion, or pinched sections.
• Look for oil leaks around the timing cover or CMP area; oil can contaminate the sensor or wiring.

C. Electrical tests (CMP circuit)

• Power and ground:
  • With the ignition off, back-probe the CMP harness connector to verify the 5V reference (to the sensor) and ground are solid. Use the service manual to identify the exact reference pin.
  • With the ignition on, verify that the CMP sensor receives stable 5V reference and a solid ground.
• Signal circuit integrity:
  • Check continuity of the CMP signal wire from the sensor to the PCM/engine CPU harness. Look for opens or high resistance.
  • Check for shorts to power or ground on the CMP signal wire.
• Sensor resistance (if applicable):
  • Some CMP sensors provide an internal resistance range; compare measured resistance to the expected spec from Honda’s service data. (Specs vary by engine, so consult the exact CMP spec for your engine code.)
• Inspect the PCM/ECU ground strap and connectors if electrical symptoms point to a potential ECU issue.

D. Sensor-specific tests

• CMP sensor replacement test (non-destructive):
  • If electrical checks indicate a fault or if the sensor is damaged or has a poor electrical connection, consider replacing the CMP sensor with a good-quality (OEM or reputable aftermarket) unit.
  • After replacement, clear codes, start/test drive, and re-scan to ensure the code does not return.
• If available, test CMP signal with an oscilloscope or a scope-enabled scanner to assess signal shape and timing. A healthy CMP signal is a clean PWM-like waveform; a flatline or erratic waveform indicates sensor or circuit fault.

E. Mechanical timing check (only if electrical checks point to timing concerns or if symptoms persist)

• If there is suspicion of timing misalignment (stretched chain, jumped timing, tensioner failure), a timing inspection is warranted.
• Important: Accessing timing components usually requires removing parts of the timing cover. This is a more advanced job and can cause severe engine damage if done incorrectly.
• If timing is found out of spec, perform the appropriate timing repair (chain/ tensioner/ guides, or re-timing with factory procedure). After timing work, recheck CMP signal and engine start/run.

F. After repair validation

• Clear the DTCs with a scan tool after repair and perform a careful test drive under varied conditions (idle, light and moderate throttle, high RPM if safe).
• If P0340 recurs, re-check all wiring, sensor integrity, and timing components; consider PCM health if no faults found in hardware.

RELATED CODES

• P0341 Camshaft Position Sensor Circuit Range/Performance (A)
• P0342 Camshaft Position Sensor Circuit Low Input (A)
• P0343 Camshaft Position Sensor Circuit High Input (A)
• P0335 Crankshaft Position Sensor A Circuit
• P0010 Camshaft Position Actuator/Timing Over-Advanced (if your engine uses a VVT/cam timing actuator and the related solenoid/valve has an issue)
• P0011 Camshaft Position Timing Over-Retarded (similar family when VVT is involved)
  Note: The exact bank/sensor labeling (A/B) may vary by engine. Use the diagnostic context and service data for your specific Accord engine code.

REPAIR OPTIONS AND COSTS (2025 prices)

Prices vary by region, shop, and whether you use OEM or aftermarket parts. The ranges below are typical for 2018-2023 Honda Accord engines.

A. Camshaft Position Sensor (CMP) replacement

• Part cost:
  • Aftermarket CMP sensor: roughly $25–$120
  • OEM/Honda CMP sensor: roughly $70–$180
• Labor:
  • Typical 0.5–1.0 hour at $75–$150/hr
• Typical total: approximately $120–$300 (sensor plus labor). If sprinting labor rates are higher in your area, expect a higher total.

B. Timing chain/tensioner/guide related repairs (only if timing issue found)

• Parts:
  • Timing chain, tensioner, guides, gaskets: $150–$600 (varies by engine and whether you replace related guides, water pump, etc.)
• Labor:
  • 4–8+ hours (engine-specific; Honda timing work is moderate to advanced)
• Typical total: $800–$2,500+, depending on extent of work and whether water/oil pump or other components are included.

C. Crank/CMP/ECU concerns beyond sensor replacement

• PCM/ECU repair or replacement is rare but possible if wiring checks point to ECU input failure.
• PCM replacement could be $300–$800 for core+labors, plus programming fees if required.

D. Miscellaneous

• Gaskets, seals, and fluids if you open the timing cover or remove components (oil change, oil filter), typically adds $20–$100.
• Diagnostic fees at shops: often $100–$150 (plus parts and labor if a diagnostic charge is included).

DIY VS PROFESSIONAL

• DIY-friendly scenarios:
  • Replacing CMP sensor is typically within DIY capability for a mechanically inclined installer with basic tools. Steps involve disconnecting battery, removing the electrical connector, unbolting the sensor, replacing it, and reassembling. Reconnect battery, clear codes, and test drive.
  • Visual inspection of sensor wiring and connectors is a good DIY starting point.
• When to go professional:
  • Suspected timing chain/belt issues, tensioner failure, or vibration that could indicate internal engine timing problems.
  • Intermittent, hard-to-diagnose electrical faults, especially if you don’t have access to an oscilloscope or advanced diagnostic tools.
  • If the CMP replacement does not resolve the issue or if the PCM/ECU could be implicated.
  • If you’re not comfortable with removing parts from the timing cover, or you’re uncertain about timing procedures. Incorrect timing can cause significant engine damage.
• Safety and reliability:
  • Always disconnect the battery when working on electrical connectors.
  • Work on a cool engine, in a clean area, and use proper torque specs when fasteners are involved.
  • After any major mechanical repair, verify timing alignment and re-check for codes.

PREVENTION

• Regular oil changes with the manufacturer-recommended viscosity and interval to keep CMP area clean and reduce sludge/oil intrusion risk.
• Use good quality oil; avoid cheap/oil-erosion additives that can affect sensor signals.
• Address oil leaks promptly. Persistent oil exposure to the CMP/wiring can degrade sensor operation.
• Inspect CMP sensor wiring during routine maintenance (especially if you’ve had timing cover work or oil leaks in that area).
• Ensure connectors are clean, dry, and properly seated with locking tabs engaged.
• If you’ve done timing-related work, use the correct timing procedure and tools; don’t skip steps or reuse worn timing components.
• For engines with VVT, ensure the VVT solenoid and related actuators are functioning properly; malfunctioning VVT components can indirectly affect cam timing signals and CMP readings.

Final notes and data limitations

• The provided data states: No NHTSA complaints found for this make/model/year/issue combination, and no recalls found. This means the diagnostic guidance here is based on general OBD-II and Honda-specific knowledge, not a documented prevalence of P0340 for this exact model/year in the NHTSA data you provided.
• If you have access to additional sources (TSBs, dealership bulletins, or a factory service manual for your exact engine code), those should be consulted to confirm any model-year-specific CMP sensor wiring or timing service procedures.
• If the code returns after repair attempts, re-check all wiring and consider additional diagnostics for related systems (crankshaft position sensor, VVT system, PCM input circuitry) or consult a Honda specialist.

If you’d like, I can tailor this to your exact Accord engine code (e.g., 1.5T vs 2.0T) or help you assemble a step-by-step test plan based on the engine you own.