OBD-II trouble code
P0343: Camshaft Position Sensor "A" Circuit High (Bank 1 or Single Sensor)
SAE J2012: Camshaft Position Sensor "A" Circuit High (Bank 1 or Single Sensor). The signal is above the expected range. The chart says whether that is a short to voltage, an open on a biased input, or a failed sensor. Some engines keep running on the crankshaft signal. Some do not.
Quick facts
- System
- Powertrain
- Category
- Sensors / Timing
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $200 – $400 (camshaft position sensor replacement)
- DIY difficulty
- Intermediate DIY
Browse every code in P0300–P0394, or start from the full code library.
What does P0343 mean?
P0343 is the 'circuit high input' member of the bank-1 camshaft position sensor 'A' family — the electrical opposite of P0342. The CMP sensor reports camshaft position so the PCM can identify cylinder sequence for sequential injection and manage variable valve timing. P0343 sets when the voltage on that circuit stays above the expected range: the signal is pulled or biased high beyond a normal cam waveform. It's a level complaint, distinct from P0340 (general circuit fault), P0341 (range/performance), P0342 (level too low), and P0344 (intermittent).
A high reading can be a signal wire shorted to voltage, including where a harness chafes against a powered wire, a wiring fault that biases the circuit up, or a sensor outputting incorrectly. An open or high-resistance signal connection leaves the line near supply only on the module inputs built that way. The wiring diagram says whether this input is biased that way. A failed sensor can also drive its output high. On a powered three-wire cam sensor, a supply or reference-circuit problem can push the signal above the published spec. The pattern is not the complaint, so the circuit is tested for a short to voltage and for an abnormal supply. Oil in the connector can corrode the terminals. That is a connector finding, not a claim that oil on the sensor tip raises the voltage.
The operational impact mirrors P0342 and is generally milder than a crankshaft fault. Many engines fall back on the crank signal to keep running, so the symptom is often a long crank or hard start, an occasional stumble, reduced power, or disabled variable valve timing rather than a complete no-start — though some vehicles that rely on the cam signal for sync may still fail to start. It should be fixed because degraded cam sync hurts driveability and emissions. Diagnosis starts at the connector: inspect for corrosion, damage, and oil intrusion, check the signal wire for a short to voltage, verify supply and ground on a powered sensor, and confirm the sensor's output before replacing it.
Common causes
- Short to a voltage source in the CMP signal wire, often from a chafed harness
- Open or high-resistance connection in the signal circuit — on some module input designs that leaves the line sitting near supply rather than being pulled down, so check the wiring diagram for how the input is biased
- Wiring fault biasing the circuit above its normal range
- Failed CMP sensor driving its output high
- Supply or reference-circuit problem on a powered (three-wire) sensor
- Oil contamination on the sensor or connector corrupting the signal
- Damaged insulation letting the signal wire contact a powered circuit
Symptoms
- Check engine light with P0343 stored
- Long crank or hard start
- Occasional stumble, hesitation, or reduced power
- Variable valve timing disabled, with slightly rougher running
- Intermittent no-start on vehicles that rely on the cam signal for sync
- Slightly reduced fuel economy
Diagnostic steps
- 1.Inspect the CMP sensor connector for corrosion, damage, and oil intrusion as a first, quick check.
- 2.Check the signal wire for a short to voltage — look closely where the harness could chafe against a powered wire.
- 3.On a powered sensor, verify supply voltage, reference, and ground are within spec, since a supply fault can bias the signal high.
- 4.Scope or meter the sensor output during cranking; a level that stays above spec confirms the high-input condition. Before anyone cranks, route the leads clear of the belt, pulleys and cooling fan and keep hands and sleeves out of them — the engine may fire rather than just turn over.
- 5.Test wiring continuity and resistance back to the PCM for faults that would skew the reading.
- 6.Replace the sensor only after the wiring, connector, and supply circuits all check out.
Repair cost
$200 – $400 (camshaft position sensor replacement)
Camshaft position sensor replacement, parts plus labor. This $200–$400 range is that sensor replacement. RepairPal's national average for the camshaft position sensor is about $224–$326. A short to voltage or a connector repair is wiring labor and is not included in this sensor price. An oil leak onto the sensor is its own job. Fix that leak at the same time, or the replacement is back in the same oil.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with camshaft position sensor replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.