The P0340 code in your 2018 Toyota Sienna indicates a camshaft position sensor circuit malfunction on bank 1. Combined with stalling at idle, this points to either a failing sensor or circuit issues that prevent the ECM from tracking camshaft position—critical information for fuel injection and ignition timing.
Why Camshaft Position Matters
The ECM uses the camshaft position sensor to determine which cylinder is on its compression stroke for sequential fuel injection timing. Without this information, fuel delivery becomes imprecise, causing rough running and potentially stalling. The sensor works alongside the crankshaft position sensor for complete engine timing.
The 2018 Sienna Engine
Your Sienna uses the 3.5L V6 (2GR-FKS) with dual VVT-i (variable valve timing). Bank 1 is the side containing cylinder 1 (passenger side). The camshaft position sensor monitors the intake camshaft and provides feedback for VVT-i operation as well as injection timing.
Common Causes
The camshaft position sensor itself may have failed. Wiring or connector issues interrupt signal to ECM. Oil contamination on the sensor from leaks can affect readings. The sensor's reluctor ring (on the camshaft) may be damaged. VVT-i actuator issues can affect sensor readings indirectly.
Diagnostic Steps
Using Toyota Techstream, verify the P0340 code and check for related codes. Monitor camshaft position sensor signal—it should produce a consistent pattern. Check sensor resistance and wiring continuity. Inspect the sensor for oil contamination. Compare bank 1 and bank 2 sensor signals if possible.