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P0343 — Cam Position Sensor High Input (Bank 1)

P0343 is set when the ECM sees the Bank 1 "A" camshaft position sensor circuit sitting above its calibrated maximum voltage. On most engines "A" is the intake camshaft, or the single cam sensor on engines with only one. Because a Hall-effect cam sensor normally idles near reference voltage and pulls the line low as each reluctor tooth passes, a circuit stuck high usually means the sensor is not pulling at all: an open signal or ground circuit, a short to a power source, or a dead sensor. P0343 is the mirror image of P0342.

P0343 means cam position sensor high input (bank 1). A vehicle usually stays drivable short-term with this code, but it should be diagnosed promptly. The most common cause is open circuit in the cam sensor signal wire or its ground (typically $80–$350). Causes and cost vary by make and model; confirm the root cause before replacing parts.

Severity: high powertrain Safe to drive (short term)

Reviewed by MECH AI Editorial · Last verified

What does P0343 mean?

P0343 is set when the ECM sees the Bank 1 "A" camshaft position sensor circuit sitting above its calibrated maximum voltage. On most engines "A" is the intake camshaft, or the single cam sensor on engines with only one. Because a Hall-effect cam sensor normally idles near reference voltage and pulls the line low as each reluctor tooth passes, a circuit stuck high usually means the sensor is not pulling at all: an open signal or ground circuit, a short to a power source, or a dead sensor. P0343 is the mirror image of P0342.

What are the symptoms of P0343?

What causes P0343?

Cause Likelihood Estimated repair (USD)
Open circuit in the cam sensor signal wire or its ground Most common $80–$350
Failed camshaft position sensor (output stuck high) Most common $100–$400
Cam sensor signal wire shorted to a power source Common $80–$350
Corroded connector adding resistance to the signal or ground path Common $50–$250
Loose or incorrectly torqued sensor leaving the air gap too large — Costs nothing to check — a sensor backed out of its bore reads high because it never sees the reluctor. Occasional $20–$100
Damaged or missing teeth on the camshaft reluctor / tone wheel Occasional $300–$1,200
Failed PCM input for the cam sensor circuit Rare $400–$1,500

Repair costs are typical US ranges and vary by make, model, model year, and labor rate. A diagnostic trouble code is a symptom, not a guaranteed failed part — confirm the root cause before replacing anything.

Is it safe to drive with P0343?

In most cases a vehicle stays drivable for short trips with P0343 active, but you should diagnose and repair it promptly. This is a high-severity code — ignoring it can lead to further damage or a failed emissions test. Exact tolerance depends on your specific make and model.

How to diagnose P0343

  1. Confirm the sensor is seated and torqued

    Before any electrical testing, check that the sensor is fully seated in its bore and its bolt is tight. A sensor backed out even a few millimetres — by a loose bolt, a missing spacer, or a previous repair — sits too far from the reluctor to trigger and reports a permanently high circuit. This is a five-minute check that occasionally ends the whole diagnosis.

    Tools: Socket set, Torque wrench

  2. Inspect the connector and harness

    Unplug the sensor and look for pushed-back or corroded pins, oil intrusion, and chafing where the harness crosses brackets or the valve cover. High-input codes are frequently a poor ground connection, and a green crusty ground pin is the visual signature of one.

    Tools: Connector unlock tool, Flashlight, Electrical contact cleaner

  3. Check the ground circuit resistance

    With the connector unplugged, measure resistance from the sensor's ground pin to a known-good chassis ground. It should be very close to zero. Anything more than a couple of ohms is a bad ground, and a bad ground is one of the most common reasons a perfectly good sensor reports high.

    Tools: Multimeter, Wiring diagram

  4. Test the signal circuit for a short to power

    Unplug both the sensor and, if you can access it safely, the ECM connector. Measure the signal wire against ground with the key on. Voltage present on a wire that is disconnected at both ends means it is touching a power source somewhere along its run — find and repair the chafe point.

    Tools: Multimeter, Wiring diagram

  5. Scope the signal during cranking

    Capture the waveform while cranking. A working sensor produces clean square pulses that swing from reference voltage down toward ground. A flat trace sitting at the top rail confirms the sensor is never switching — either it is dead, or the reluctor is not passing close enough to trigger it.

    Tools: Oscilloscope, Back-probe pins

How do I fix P0343?

P0343 by make and model

Select your exact year, make, and model below to get a P0343 diagnosis tuned to your vehicle's known failure patterns, recalls, and TSBs.

P0343 on Chevrolet

P0343 on Ford

P0343 on GMC

P0343 on Honda

P0343 on Hyundai

P0343 on Jeep

P0343 on Kia

P0343 on Mazda

P0343 on Nissan

P0343 on Ram

P0343 on Subaru

P0343 on Toyota

Related diagnostic codes

Common symptoms of P0343

P0343 often shows up as one of these symptoms. Start from what your car is actually doing:

P0343: frequently asked questions

What does diagnostic trouble code P0343 mean?

P0343 is set when the ECM sees the Bank 1 "A" camshaft position sensor circuit sitting above its calibrated maximum voltage. On most engines "A" is the intake camshaft, or the single cam sensor on engines with only one. Because a Hall-effect cam sensor normally idles near reference voltage and pulls the line low as each reluctor tooth passes, a circuit stuck high usually means the sensor is not pulling at all: an open signal or ground circuit, a short to a power source, or a dead sensor. P0343 is the mirror image of P0342.

What are the symptoms of P0343?

Check Engine Light is illuminated. Hard start with extended cranking. Possible complete no-start condition. Stalling, sometimes intermittent. Rough running and reduced power. Hesitation under acceleration. Reduced fuel economy

What causes P0343?

Open circuit in the cam sensor signal wire or its ground (most-common). Failed camshaft position sensor (output stuck high) (most-common). Cam sensor signal wire shorted to a power source (common). Corroded connector adding resistance to the signal or ground path (common). Loose or incorrectly torqued sensor leaving the air gap too large (occasional). Damaged or missing teeth on the camshaft reluctor / tone wheel (occasional). Failed PCM input for the cam sensor circuit (rare)

Is it safe to drive with P0343?

In most cases a vehicle stays drivable for short trips with P0343 active, but it should be diagnosed and repaired promptly — this is a high-severity code. Ignoring it can lead to further damage or a failed emissions test. Specific tolerance varies by make and model.