How is P0343 different from P0342?

They're mirror images on the same bank-1 camshaft sensor circuit. P0342 is 'circuit low input' — the signal is below the expected range, usually from a short to ground, an open, or a lost supply. P0343 is 'circuit high input' — the signal is above the expected range, usually from a short to voltage or a circuit biased high. The symptoms and consequences are the same, but the wiring fault you're hunting is opposite: low points toward ground shorts and opens, high points toward voltage shorts.

What usually causes a high-input camshaft code?

Most often a short to voltage in the signal wiring — typically where a harness has chafed through its insulation and the cam signal wire touches a powered circuit, pulling the reading high. Connector corrosion that adds resistance and supply-circuit faults on powered sensors are next. The sensor can fail high too, but because wiring and connector issues are common and cheaper, inspect the harness and connector and test for a short to voltage before replacing the sensor.

Can I keep driving with P0343?

Usually for a short time. Many engines keep running on the crankshaft signal, so you may only notice a long crank, a stumble, or reduced power rather than an immediate breakdown. The trade-offs are degraded driveability, possibly disabled variable valve timing, and the chance that some vehicles won't restart if they rely on the cam signal for initial sync. It's less urgent than a crank-sensor fault, but get it diagnosed before it turns into a hard-start headache.

Should I check anything beyond the sensor?

Yes — check the connector and wiring before assuming the sensor is bad, since a short to voltage or a corroded connector causes the same high reading for less money. Also look for oil contamination, because cam sensors often sit in oily spots and a leak can foul the sensor or connector. Confirm supply and ground on a powered sensor too. Only after the circuit, connector, supply, and ground all test good should you replace the sensor itself.

OBD-II trouble code

P0343: Camshaft Position Sensor "A" Circuit High Input (Bank 1)

The camshaft position sensor circuit on bank 1 is reading too high — the voltage has climbed above its expected window, usually from a short to voltage, a connector or wiring fault, or a failed sensor. As the mirror of the low-input code P0342, it carries the same milder consequences: because many engines run on the crank signal alone, you'll often see a hard start or stumble rather than a dead no-start.

Quick facts

System: Powertrain
Category: Sensors / Timing
Severity: Medium severity
Drivable: Usually safe to drive short-term
Repair cost range: $120 – $500
DIY difficulty: Intermediate DIY

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 usually traces to the circuit being pulled toward voltage or to a sensor outputting incorrectly. The classic causes are a short to a voltage source in the signal wire — often where a harness chafes against a powered wire — a corroded or damaged connector adding resistance that skews the reading high, a wiring fault biasing the circuit up, and a sensor that has failed in a way that drives its output high. On powered (three-wire) cam sensors, a supply or reference-circuit problem can push the signal above spec. As with all level faults, the pattern isn't the issue, so meter and scope testing of the circuit for shorts to voltage and abnormal supply is the productive path. Oil contamination around the sensor, common in the cam-sensor location, can also corrupt the reading.

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
Corroded or damaged connector adding resistance that skews the reading high
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.
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

$120 – $500

A camshaft position sensor replacement generally runs $120-$350 with labor, depending on access. Repairing a short to voltage or a chafed wire, or fixing a connector, can be less but takes diagnostic time to locate. Powered-sensor supply faults are wiring labor rather than a part. If oil contamination is present, address the leak as well. Diagnosis is usually straightforward.

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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.