# P0340: Camshaft Position Sensor "A" Circuit (Bank 1 or Single Sensor) **Verdict:** Drive to a shop this week Engine sensors - Generic OBD-II code, applies to all gasoline cars and light trucks sold in the US since 1996. - **Typical cost:** $120-$450 - **Urgency:** This week - **Most likely:** Failed cam sensor or its wiring - **DIY?:** Often, if easy to reach ## Quick answer P0340 means the engine computer is not getting a proper signal from the camshaft position sensor on bank 1 (or the only cam sensor on some engines). The computer uses this sensor to know which cylinder is on its firing stroke, so a missing signal can cause hard starting or stalling. The usual causes are a failed sensor or a wiring problem. ## What does P0340 mean? The camshaft position sensor watches a notched wheel or lobe on the camshaft, which turns once for every two turns of the crankshaft. Its pulses tell the engine computer which stroke each cylinder is on, so it can fire the injectors in sequence and, on many engines, time individual ignition coils. On engines with variable valve timing, the computer also uses it to check that the cam is where it was commanded. P0340 is a circuit code for camshaft sensor "A" on bank 1, or the only cam sensor. It sets when the computer sees no signal, or one that is missing pulses, while the crankshaft sensor shows the engine is turning. On engines with more than one cam sensor, "A" usually means the intake cam, and bank 1 is the side that holds cylinder 1. Some engines can start and run on crank data alone, but cranking takes longer. ## What are the symptoms of P0340? - Check engine light on - Long cranking before the engine starts - Engine stalls or will not start - Rough running or reduced power ## What causes P0340? Ranked from most to least likely. Check them in this order: the cheap, common causes first. 1. **Failed camshaft position sensor** (most common). Cam sensors live on the cylinder head or timing cover, where heat cycles and engine oil can work into the sensor body. Internal failure shows as long cranking, stalling or a no-start, often worse when hot. On some engines oil wicks through the sensor into its wiring. A scope or scan tool shows whether pulses are present while cranking. 2. **Damaged wiring or loose connector** (common). Most cam sensors have three wires: a reference voltage, a ground and a signal back to the computer. A broken wire, corroded pin, oil-soaked connector or plug that has backed out interrupts the pulses. The wiring often runs near the timing cover or exhaust, where heat makes insulation brittle. Wiggle-testing while watching the signal finds intermittent faults. 3. **Weak battery or low cranking speed** (less common). During cranking, a weak battery or a poor cable connection lets system voltage drop and the engine turn slowly. The cam signal may then look weak or erratic, and the computer can set P0340 even though the sensor is fine. Cold mornings and aging batteries make this more likely. Test the battery and clean its connections before buying a sensor. 4. **Timing belt or chain problem** (rare). A timing belt that has slipped or broken, or a timing chain that has jumped a tooth, stops the camshaft from turning in step with the crankshaft. If the cam stops entirely, there is no signal at all. This usually brings codes such as P0016, plus a no-start or very rough running. On interference engines it can bend valves. ## How do you diagnose P0340? 1. Read all codes. A P0340 together with P0335 points to shared wiring or a power supply problem. 2. Inspect the cam sensor connector and wiring for oil intrusion, corrosion, or damage. 3. Check that the sensor has power and ground, then watch its signal with a scan tool or scope while cranking. 4. If the sensor and wiring are fine, check cam and crank timing alignment. ## How do you fix P0340, and what does it cost? | Fix | Typical cost | What it involves | | --- | --- | --- | | Replace camshaft position sensor | $120-$350 | Usually a bolt-in part on the cylinder head or timing cover. | | Repair sensor wiring or connector | $120-$350 | Fixes a damaged wire, corroded pins, or a loose plug. | | Repair timing belt or chain | $600-$2,500 | Only if timing has slipped. Price depends heavily on the engine. | Full price breakdowns: [timing belt replacement cost](/cost/timing-belt-replacement), [timing chain replacement cost](/cost/timing-chain-replacement). ## Is it safe to drive with P0340? > **Drive to a shop this week.** Many cars still run with this code, but stalling and no-starts are possible. Get it repaired soon and avoid long trips until it is fixed. ## Will P0340 fail an emissions test? A vehicle with P0340 and the light on fails an OBD-based emissions inspection. Some cars also fall back to a less precise fuel mode or disable variable valve timing while the code is active, which can hurt emissions and fuel economy. Once the sensor or wiring is repaired, clear the code and drive normally until the readiness monitors are complete. ## After the repair: clearing P0340 Clear the code, then start the engine several times, both cold and fully warm, checking that cranking is short and normal. Watch for codes such as P0011 or P0016 appearing, which would point to cam timing rather than the sensor. If starts are quick and the light stays off through a week of driving, the repair worked. ## How to prevent P0340 - Change oil on schedule; sludge can upset variable valve timing and gum up sensor tips. - Fix oil leaks at the sensor O-ring or valve cover before oil seeps into the connector. - Replace a weak battery before slow cranking starts making the cam signal look erratic. - Replace the timing belt at the maker's interval so timing never slips or snaps. ## Codes often seen with P0340 - [P0341](/codes/p0341): Camshaft Position Sensor "A" Circuit Range/Performance (Bank 1 or Single Sensor) - [P0335](/codes/p0335): Crankshaft Position Sensor "A" Circuit - [P0016](/codes/p0016): Crankshaft Position - Camshaft Position Correlation (Bank 1 Sensor A) - [P0011](/codes/p0011): "A" Camshaft Position - Timing Over-Advanced or System Performance (Bank 1) - [P0010](/codes/p0010): "A" Camshaft Position Actuator Circuit (Bank 1) ## Frequently asked questions ### Can I drive with a P0340 code? Often yes for a short time, but the engine may stall or fail to restart, especially when hot. That can leave you stranded or stall you in traffic. Get it to a shop soon, avoid long trips, and stop driving if the engine also starts running very rough. ### What is the difference between P0340 and P0341? P0340 means the computer sees no usable signal from the cam sensor circuit. P0341 means a signal is there but does not line up with what the crankshaft sensor reports. P0340 leans toward a dead sensor or broken wire, while P0341 adds the possibility of a timing problem. ### Is a camshaft position sensor easy to replace? On many engines it is held by one bolt and takes under an hour with basic tools. Clean the mounting area, use the new O-ring and do not force the sensor into its bore. Check the wiring and connector at the same time, since a bad plug can cause the same code. ### Can a bad battery cause P0340? Yes, a weak battery can cause slow cranking that makes the cam signal look wrong. Test the battery and clean its terminals before replacing the sensor if the car is also slow to crank. If the code disappears after a battery fix, the sensor was probably fine all along. ### How much does it cost to fix P0340? Most P0340 repairs cost $120 to $350 for a new sensor or a wiring repair at an independent shop. The sensor is usually a bolt-in part, so labor is short. Only when testing shows a slipped timing belt or chain does the cost climb to $600 to $2,500, depending on the engine. ### Where is the camshaft position sensor? It is usually on the cylinder head, often at the top or rear of the engine, or on the timing cover at the front. Engines with two or four camshafts may have several sensors, so make sure you are working on sensor A for bank 1. Service information shows the exact location. ### Should I replace the cam and crank sensors together? Not unless both test bad. P0340 points to the cam sensor circuit, and the crank sensor may be fine. If both codes appear together, check the shared reference voltage and ground first, since one bad wire can knock out both sensors before you replace any parts. ### Can P0340 cause a no-start? Yes, on some engines a missing cam signal causes long cranking or a no-start, especially after the engine is shut off hot. Other engines start on the crank signal alone, just more slowly. If the tachometer moves while cranking, the crank sensor is working, so the cam circuit is a strong suspect. ### Can a bad cam sensor hurt fuel economy? Yes. When the cam signal is missing, some engines switch to a less precise backup fuel mode, and variable valve timing may be disabled. That costs fuel economy and some power. Mileage usually returns to normal once the sensor or wiring is repaired and the code is cleared. ### Will P0340 pass inspection? No, P0340 with the check engine light on fails an OBD-based emissions inspection. After the repair, clear the code and drive a few days of normal mixed trips. Confirm with a scan tool that the readiness monitors are complete, then return so the station does not turn the car away. ## Sources - [SAE J2012: Diagnostic Trouble Code Definitions](https://www.sae.org/standards/content/j2012_201812/) ## Other engine sensors codes - [P0327 Knock Sensor 1 Circuit Low (Bank 1 or Single Sensor)](https://diagxcar.com/codes/p0327) - [P0332 Knock Sensor 2 Circuit Low (Bank 2)](https://diagxcar.com/codes/p0332) - [P0335 Crankshaft Position Sensor "A" Circuit](https://diagxcar.com/codes/p0335) - [P0336 Crankshaft Position Sensor "A" Circuit Range/Performance](https://diagxcar.com/codes/p0336) - [P0339 Crankshaft Position Sensor "A" Circuit Intermittent](https://diagxcar.com/codes/p0339) - [P0341 Camshaft Position Sensor "A" Circuit Range/Performance (Bank 1 or Single Sensor)](https://diagxcar.com/codes/p0341) - [P0344 Camshaft Position Sensor "A" Circuit Intermittent (Bank 1 or Single Sensor)](https://diagxcar.com/codes/p0344) - [P0345 Camshaft Position Sensor "A" Circuit (Bank 2)](https://diagxcar.com/codes/p0345) - [P0351 Ignition Coil "A" Primary/Secondary Circuit](https://diagxcar.com/codes/p0351) - [P0352 Ignition Coil "B" Primary/Secondary Circuit](https://diagxcar.com/codes/p0352) - [P0010 "A" Camshaft Position Actuator Circuit (Bank 1)](https://diagxcar.com/codes/p0010) - [P0011 "A" Camshaft Position - Timing Over-Advanced or System Performance (Bank 1)](https://diagxcar.com/codes/p0011) - [P0016 Crankshaft Position - Camshaft Position Correlation (Bank 1 Sensor A)](https://diagxcar.com/codes/p0016) - [P0320 Ignition/Distributor Engine Speed Input Circuit](https://diagxcar.com/codes/p0320) ## Symptoms - [Why does my car crank but not start?](https://diagxcar.com/symptoms/car-cranks-but-wont-start) - [Why does my car stall while driving?](https://diagxcar.com/symptoms/car-stalls-while-driving) - [Why won't my car start?](https://diagxcar.com/symptoms/car-wont-start) ## Repair costs - [Timing belt replacement cost](https://diagxcar.com/cost/timing-belt-replacement): $500-$1,300 - [Timing chain replacement cost](https://diagxcar.com/cost/timing-chain-replacement): $1,200-$3,500 - [Camshaft position sensor replacement cost](https://diagxcar.com/cost/camshaft-position-sensor-replacement) --- Source page: https://diagxcar.com/codes/p0340 Updated: 2026-11-03 General information, not a substitute for a qualified mechanic.