Your 2021 Sonata dies at red lights and stop signs, leaving you scrambling to restart in traffic. The P0340 code points to the camshaft position sensor—a critical component for engine timing. When this sensor fails or sends erratic signals, stalling is a common result.
What P0340 Indicates
The P0340 code means "Camshaft Position Sensor Circuit Malfunction (Bank 1)." The camshaft position sensor tells the engine computer exactly where the camshaft is in its rotation. This information is essential for fuel injection timing and spark timing.
Why It Causes Stalling
The engine computer needs constant updates on camshaft position to run properly. When the signal drops out or becomes erratic:
- Fuel injection timing becomes random
- Spark timing is compromised
- The engine can't maintain idle
- Stalling occurs, especially at low RPM
Stalling Symptoms
- Engine dies when coming to a stop
- Rough idle before stalling
- Difficult or extended restart
- May run fine at speed, die when slowing
- Check engine light with P0340
Common Causes
- Failed CMP sensor: Internal sensor failure
- Wiring damage: Broken or corroded wires to sensor
- Connector issue: Loose or corroded connection
- Timing chain stretch: Creates out-of-range readings
- Oil contamination: Oil-soaked sensor or connector
Diagnosis Steps
- Check connector condition and security
- Inspect wiring for damage or oil contamination
- Test sensor resistance against specifications
- Monitor sensor signal with oscilloscope if available
- Check for timing chain noise or codes
Repair Costs
- CMP sensor: $100-$300
- Wiring repair: $100-$250
- Connector replacement: $50-$150
- Timing chain service: $800-$2,000 (if related)