P0340high severityDo not driveP0340 Code: Camshaft Position Sensor Circuit Malfunction
Written in plain English and reviewed by the eli5cars editorial team · Last reviewed June 2026
What it means in plain English
The camshaft position sensor tells your engine's computer exactly where the camshaft is in its rotation at any given moment. The ECM uses this information — combined with the crankshaft position sensor — to precisely time fuel injection and, on engines with distributorless ignition, spark delivery. P0340 means the ECM is getting no signal, an erratic signal, or an out-of-range signal from the camshaft position sensor circuit. Without this data, the ECM may not know when to fire the injectors, which can cause hard starts, stalling, or a complete no-start condition. This is a timing-critical signal — don't ignore it.
⛔ Do not drive with this code active
This fault can cause immediate mechanical or safety damage. Have the vehicle towed or inspected before driving.
Most likely causes — ranked
#1 Failed camshaft position sensor
most likelyFix: The sensor itself fails due to heat, age, or internal component failure. The camshaft position sensor is typically mounted near the camshaft sprocket or timing cover. Use a multimeter to check for the correct reference voltage at the sensor (usually 5 V or 12 V), a proper ground, and a signal output that changes when the engine cranks. If reference voltage and ground are present but the signal is absent, replace the sensor. Match the replacement to your exact engine.
#2 Damaged, corroded, or open wiring between the sensor and ECM
likelyFix: Inspect the harness running from the sensor connector to the ECM. Wires can chafe against engine components, melt against hot surfaces, or corrode at the connector pins. With the sensor unplugged, check for 5 V (or 12 V) reference voltage and a good chassis ground at the connector. Check signal wire continuity all the way back to the ECM. Repair any damage before replacing the sensor.
#3 Reluctor ring (tone wheel) damage or debris buildup
likelyFix: The sensor reads a reluctor ring — a toothed ring attached to the camshaft. A missing tooth, metallic debris from engine wear, or oil sludge buildup around the ring can produce an erratic or absent signal. Inspect the reluctor ring when accessing the sensor for replacement. Clean the area and inspect for tooth damage. Significant reluctor damage means the camshaft or its sprocket assembly may need replacement.
#4 Timing chain or belt stretch causing cam-to-crank correlation error
possibleFix: A worn timing chain can allow the camshaft to drift out of phase with the crankshaft. When the cam position is too far off from expected, the ECM may log P0340 alongside correlation codes like P0016. If you also see P0016, P0017, or similar, have the timing components inspected immediately — a jumped timing chain can bend valves and cause catastrophic engine damage.
Check engine light on? Get a free code scan
If your check engine light is on, most auto-parts stores (AutoZone, O'Reilly, Advance) will read the code for FREE — no purchase required, just walk in. Bring the code back here and look it up at eli5cars.com/obd2 for the plain-English explanation.
Note: a scan only helps when there's an active fault code. For purely mechanical symptoms (noises, vibrations, leaks), a scan may show nothing — the suspects listed above are your starting point.
Want to read the codes yourself?
First, the free option: AutoZone, O’Reilly, and Advance Auto Parts read your codes for free — no purchase needed. That’s the cheapest way to get the code to look up here. If you’d rather have your own so you can check anytime (and clear a code after a fix), the Veepeak OBDCheck BLE is an inexpensive, reliable plug-in reader that pairs with a free phone app and works on any car sold since 1996.
See the Veepeak OBD2 scanner on AmazonAffiliate link — we may earn a commission at no extra cost to you. Details.
Frequently asked questions
Can I drive with P0340?
You should not. P0340 can cause stalling while driving, and the engine may not restart after stalling. If your car is running but showing this code, drive directly to a repair shop and avoid the highway. If the engine won't start, diagnose it before attempting to drive.
Will P0340 cause a no-start?
Yes, it can. The ECM needs the cam sensor signal to fire fuel injectors correctly. Without it, many vehicles will crank but not start, or may barely start and stall immediately. Some vehicles have a limp-home fallback that lets the engine run roughly using crankshaft data alone, but this varies by make and model.
P0340 showed up along with P0016 — what does that mean?
That combination strongly suggests a timing issue — either a stretched timing chain, a jumped timing belt, or a VVT system fault causing the camshaft to be out of phase with the crankshaft. This is more serious than a simple sensor failure. Have the engine inspected before driving further to avoid potential valve damage.
How do I get a free scan for P0340?
AutoZone, O'Reilly, and Advance Auto Parts offer free OBD2 scans. Note all codes present — multiple codes together tell a more complete story than one code alone. If the car won't start, you'll need a scanner that can read codes without starting the engine (most standard scanners can do this with key-on/engine-off).