P0340: Camshaft Position Sensor Circuit Malfunction (Bank 1)

The camshaft position sensor works similarly to the crankshaft sensor but monitors the camshaft. While the crankshaft position is essential for ignition and injection timing, the camshaft position tells the ECU which stroke each cylinder is on (intake vs exhaust). This is critical for sequential fuel injection and variable valve timing. On interference engines, a correlation error between crank and cam signals can indicate a jumped timing chain.

Position sensors are critical for engine operation. The crankshaft position sensor tells the ECU the exact rotational position of the crank, enabling precise ignition timing and fuel injection. The camshaft position sensor identifies which stroke each cylinder is on (compression vs exhaust), enabling sequential fuel injection. Without the crank sensor, most engines will not start at all. Without the cam sensor, most engines can still run (using batch injection) but with reduced efficiency. These sensors typically use either a Hall-effect element or a variable reluctance (magnetic) element to read a toothed reluctor ring. Common affected vehicles: Chrysler/Dodge (crank sensor failures notorious in 2.0L/2.4L engines), GM (cam sensor failures in 3.6L V6), Ford (crank sensor heat failures in 4.6L/5.4L Modular V8), Nissan (cam sensor failures in VQ35DE).

Understanding P0340 in Depth: The camshaft position sensor reads a toothed reluctor ring (also called a tone ring or trigger wheel) mounted on the camshaft. As each tooth passes the sensor, it generates an electrical pulse. The ECU counts these pulses to determine both the rotational position and speed of the camshaft. A missing tooth (or multiple missing teeth) in the reluctor ring creates a signature gap that the ECU uses as a reference point for absolute position.

There are two main types of position sensors: Variable Reluctance (VR) sensors generate an AC voltage signal whose amplitude increases with speed — they don't need power and produce a sine wave. Hall Effect sensors produce a clean digital square wave signal and require a power supply (typically 5V or 12V from the ECU). The type matters for diagnosis: VR sensors can be tested with a simple AC voltmeter during cranking, while Hall sensors require checking for power supply AND signal output.

Step-by-Step Diagnosis: (1) Check for the most common failure mode: intermittent stalling or no-start that comes and goes, especially related to temperature. A sensor that works cold but fails hot (thermal failure) is the classic camshaft sensor symptom. (2) Inspect the sensor and reluctor ring for physical damage — cracked sensors, loose mounting, damaged teeth. (3) Check the air gap between sensor and reluctor — it should be 0.020-0.050 inches on most vehicles (check service manual). (4) Test the sensor: for VR sensors, measure AC voltage at the connector while cranking (should see 0.5V+ pulsing signal). For Hall sensors, check for 5V/12V power supply at the connector, then check for a switching signal during cranking. (5) Check wiring between sensor and ECU for damage, especially near heat sources.

Vehicle-Specific Notes: Chrysler/Dodge 2.0L and 2.4L engines are notorious for camshaft sensor failures — the sensor is located in a high-heat area and commonly fails between 80K-150K miles. Ford 4.6L and 5.4L Modular V8 engines develop crank sensor failures from heat soak — the engine stalls after running hot and restarts after cooling. GM 3.6L V6 engines commonly develop cam sensor failures around 100K miles. Nissan VQ35DE engines can set cam sensor codes from timing chain stretch rather than actual sensor failure.