P0340 — Camshaft position sensor A circuit — bank 1

P0340 concerns a missing, invalid or unusable camshaft-position sensor A circuit signal on bank 1 (or the single cylinder bank). The engine controller uses cam and crank signals for synchronization. An electrical or signal-path problem can trigger this code; P0340 alone does not establish mechanical timing misalignment and must not be confused with correlation DTC P0016.

Affected system: Engine position sensing

Symptoms

• Engine warning lamp and stored fault code.
• Hard starting or prolonged cranking; some engines may not start.
• Reduced power or backup-control operation depending on the engine strategy.

Possible causes

• Open/shorted CMP signal, power or ground wiring; damaged, loose or corroded pins.
• Fault in the specified CMP sensor after its sensor technology and electrical supply have been established.
• Damaged, displaced or contaminated camshaft trigger target or incorrect sensor mounting/air gap.
• Cam/crank synchronization issue related to timing or VVT only when confirmed by engine-specific waveform correlation; P0340 itself is not proof.

What to check

• 1. Record P0340, freeze-frame and related CKP, VVT and cam/crank-correlation codes (such as P0016). Ask about recent timing, sensor or engine work and whether the failure occurs while cranking or running.
• 2. Identify bank 1 and CMP sensor A from the exact engine wiring/service diagram; sensor labels and positions vary by engine. Do not test another bank's sensor by assumption.
• 3. Visually inspect the identified sensor, connector and harness near the cylinder head for oil, corrosion, heat and abrasion. Repair obvious connector or loom defects before replacing components.
• 4. Identify the sensor design and pinout first (Hall/active versus inductive where applicable). Verify the OEM-required supply, ground and circuit continuity/insulation safely; do not apply an ohmmeter resistance test across an unidentified Hall device.
• 5. With a correctly connected oscilloscope, observe CMP output during cranking or idle, following safe service precautions. A missing or intermittent waveform with proper supply/ground directs attention to the sensor, trigger target or signal wire; compare at the sensor and ECU where accessible.
• 6. If CMP and CKP waveforms are present, compare their timing with a known-good reference for the exact engine. A stable phase offset can warrant an OEM mechanical timing/VVT check, but not replacement of the timing system on the strength of P0340 alone.
• 7. If the waveform is abnormal despite sound wiring and supply, inspect sensor mounting and the trigger wheel/target using the engine-specific procedure; replace only the demonstrated defective part.
• 8. After the documented repair, clear DTCs and verify repeated starts and live CMP/CKP synchronization under the original fault conditions. If starting is unreliable or the engine stalls, arrange service rather than relying on continued driving.

Also written as: P0340-00, P034000, PO340 (some scan tools add the fault-type byte, e.g. -00).