When your 2017 Chevrolet Impala stalls at red lights and sets a P0340 code, the engine has lost its camshaft position reference. This sensor is critical for fuel injection timing, and losing its signal causes the stalling you're experiencing.
Understanding P0340
P0340 indicates a circuit malfunction in the camshaft position sensor system on bank 1—the PCM is receiving no usable signal. Unlike codes indicating an out-of-range signal, P0340 means complete signal loss. The Impala's engine may still run using crankshaft position alone, but this degraded mode is often unstable, especially at idle.
Why Stalling Occurs at Stops
At idle, the engine operates at minimum RPM with no vehicle motion to mask instability. Without camshaft position data, the PCM can't accurately time sequential fuel injection. The engine may run rough and stall when additional loads (like AC or power steering) engage at stops. The deceleration to a stop may trigger the stall if the sensor signal is intermittent.
Common Causes
The camshaft position sensor itself failing is most common. Wiring damage between sensor and PCM causes signal loss. Connector corrosion or backed-out pins disrupt the electrical connection. Oil contamination from valve cover gasket leaks can damage sensors. The reluctor ring on the camshaft (rare) can become damaged.
Diagnostic Steps
Locate the camshaft position sensor on the engine (typically near timing cover or cylinder head). Inspect the connector for corrosion or damage. Test wiring continuity between sensor and PCM. Monitor CMP signal during cranking with scan tool—absence of signal indicates failure. Check for oil leaks near the sensor that might indicate contamination.
Repair Costs
Camshaft position sensor replacement typically costs $100-$250 including labor. Wiring repair varies from $50-$200 depending on damage extent. If a valve cover gasket leak contaminated the sensor, address that simultaneously ($200-$400). Clear codes and verify proper operation after repair.