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P0340 on a 2017 Honda Civic

Camshaft Position Sensor Circuit Fault

Severity: high Safe to drive (short term) Compact Sedan 2015-2019 Honda Civic

What does P0340 mean on a 2017 Honda Civic?

P0340 is set when the engine control module cannot interpret the camshaft position sensor signal on the primary cam (or the single cam on engines with one sensor). The signal might be missing entirely, out of phase with the crankshaft signal, or showing electrical noise. Because the ECM uses cam position to time fuel injection and ignition, a P0340 will typically cause a hard start, a no-start, or a stall.

Symptoms on a 2017 Honda Civic

Likely causes on a 2017 Honda Civic

  1. Failed camshaft position sensor (most common after 100k miles) Most common
    Estimated repair: $100– $400
  2. Damaged or corroded sensor connector Common
    Estimated repair: $50– $250
  3. Chafed or broken sensor wiring Common
    Estimated repair: $80– $350
  4. Loose, slipped, or worn camshaft sensor reluctor wheel Occasional
    Estimated repair: $300– $1,200
  5. Timing chain stretch causing cam-crank correlation drift Occasional
    Estimated repair: $800– $3,000
  6. Failed PCM driver for the cam sensor input (rare) Rare
    Estimated repair: $400– $1,500

How to diagnose this on a 2017 Honda Civic

  1. Inspect the connector and wiring at the cam sensor

    Locate the cam sensor (usually near the front of the cylinder head, threaded into the head or timing cover). Disconnect the sensor and inspect the connector for corrosion, bent pins, or water intrusion. Inspect the harness for chafing against engine mounts or accessory brackets.

    Tools: Connector unlock tool, Flashlight, Electrical contact cleaner

  2. Test the sensor signal with a scope or scan tool

    With the engine cranking or running, the cam sensor should produce a square-wave or sine-wave signal that the scan tool can graph. No signal or a noisy signal indicates the sensor or its wiring is bad. A clean signal that the ECM does not respond to suggests an ECM input fault.

    Tools: Scan tool with cam sensor PID, or oscilloscope, Multimeter

  3. Verify cam-crank correlation in live data

    Watch the cam and crank position signals together while cranking. They should maintain a fixed timing relationship. If the cam signal drifts relative to the crank signal over time, suspect timing chain stretch or a slipped reluctor wheel.

    Tools: Scan tool with dual-PID graphing

  4. Check sensor power and ground at the connector

    With the connector unplugged and the key on, verify battery voltage on the power wire and continuity from the ground wire to a known good chassis ground. Missing power or poor ground will produce P0340 with a perfectly good sensor.

    Tools: Multimeter, Wiring diagram

  5. Inspect the reluctor / target wheel on the camshaft

    If the wiring tests good and the sensor is new but P0340 persists, remove the sensor and shine a light at the reluctor wheel through the sensor port. Damaged or oil-fouled teeth will not generate a clean signal. On some engines the reluctor is a separate pressed-on piece that can slip.

    Tools: Inspection mirror, Bright flashlight

Known Technical Service Bulletins for the 2015-2019 Honda Civic

Manufacturers publish Technical Service Bulletins (TSBs) when a known issue affects a specific vehicle. These bulletins come from the NHTSA database for your Honda Civic.

+14 more TSBs available in MECH AI's TSB explorer for this vehicle.

Common fixes

About the 2015-2019 Honda Civic

The 2015-2019 Honda Civic was commonly sold with the following powertrains: 2.0L I4, 1.5L Turbo I4, 1.8L I4. Common trims include LX, Sport, EX, Touring.

Why P0340 sometimes causes a no-start

The ECM uses the cam sensor to decide which cylinder is approaching top-dead-center on the compression stroke vs. the exhaust stroke. With no cam signal, the ECM cannot synchronize the injectors to the right cylinder, and on many engines it defaults to a fail-safe mode that disables fuel injection. The engine will crank but not fire.

Some engines (notably modern Ford and GM) have a “limp” mode that uses the crank signal alone and runs the engine in batch fire (all injectors firing together) — these vehicles will run, but poorly, without a cam signal.

Cam sensor vs. timing chain

A new cam sensor is $30–$150 and a 15-minute install on most engines. Timing chain replacement is $800–$3,000. Before condemning the chain, always test the new sensor first. The exception: on engines with documented timing chain stretch issues (BMW N20, VW EA888 1st gen, GM 3.6 LFX/LLT, Nissan VQ35 with stretched chain) and high mileage, cam-crank correlation drift in the live data should be inspected before installing a new cam sensor.

Heat-soak intermittent stalling

A failing cam sensor often works correctly when cold and fails after extended driving. The pattern is: drive 30 minutes, stop for gas, restart and the engine stalls or cranks for 10+ seconds before catching. If P0340 is intermittent and correlates with engine heat, replace the sensor preemptively — the failure mode worsens until eventually the vehicle will not start at all.

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