P0340 Camshaft Position Sensor Circuit Fault

What it means

The camshaft position sensor tells the computer where the camshaft is, so it knows which cylinder is on its power stroke. P0340 means the signal from the cam sensor (A, on bank 1 or on an engine with only one) is missing or not believable.

The technical version

The computer expects a set pattern of cam sensor pulses for every two turns of the crankshaft. P0340 sets when the pulses are missing, too few or too many. Causes include a dead sensor, an open or shorted wire, a damaged reluctor (tone wheel) and, less often, timing that has jumped. Codes P0341 to P0344 narrow the fault to range, low or intermittent signals.

Official name: Camshaft Position Sensor Circuit Malfunction.

Symptoms

• Long cranking before the engine starts.
• Stalling or cutting out.
• Rough running or less power.
• Sometimes no start.

Causes, most likely first

How likely is our ranking from repair data and common practice, not a published rate.

What the live data shows

Cam sensor signals are not standard OBD data, so a shop confirms them with a scope. Standard data still helps: the freeze frame shows whether it set while cranking or driving, and a weak battery during cranking shows in the voltage. Many cars show no symptom between drops of the signal.

What to check first, in order

1. Read the freeze frame and companion codes.

   It shows when the signal dropped and whether timing codes came with it.

   What the data shows: Rpm, coolant temperature and voltage when it set.

   Cost: no cost if you have a scanner

2. Inspect the sensor connector and wiring.

   Oil leaks and chafed wires are common.

   What the data shows: No reading needed.

   Cost: free to look

3. Check the battery and charging voltage.

   Low voltage during cranking can upset sensor signals.

   What the data shows: About 12.4 V or more engine off, about 13.5 to 14.7 V running.

   Cost: no cost if you have a scanner

4. Replace the camshaft position sensor.

   The usual fix.

   What the data shows: Starts are quick and the code stays away.

   Cost: $224-$326 at a shop (Camshaft position sensor replacement, RepairPal)

Is it safe to drive?

Get it checked soon

Yes, fix soon. Many engines run on the crank sensor alone, but some stall or will not restart.

Many cars keep running with this code, using the crankshaft sensor alone, but starts can take longer and some engines stall or refuse to restart. Avoid long trips until it is fixed, and stop if the engine starts cutting out.

Stop driving and get help if

• The engine stalls or cuts out while driving.
• The engine will not restart after it stops.

What it costs

National averages for the full job at a shop, parts and labor, from RepairPal (updated September 3, 2026). Your price depends on the car and the area. Many of the first checks on this page cost nothing with a scanner.

Can I clear it? Will it come back?

After the repair, clear the code and do several cold and warm starts. If the signal is good, the code stays away.

Will it fail an emissions test?

Yes, while the check engine light is on, most OBD emissions tests fail the car.

Related codes

Also related, no guide yet: P0341, P0344, P0345.

Questions people ask

Can I drive with P0340?

Often for short trips, but the engine can stall or refuse to restart. Get it fixed soon.

Will a bad cam sensor cause a no start?

On some engines, yes. Many start, but take longer.

Is P0340 always the sensor?

Usually, but check the wiring and connector first, and look for timing codes.

Sources

1. RepairPal: P0340 code page repairpal.com
2. RepairPal: Check engine light diagnosis (shop) (updated September 3, 2026) repairpal.com
3. RepairPal: Camshaft position sensor replacement (updated September 3, 2026) repairpal.com
4. Texas DPS emissions testing FAQ dps.texas.gov
5. Arizona myazcar.com: OBD and the check engine light myazcar.com