P0343
Camshaft Position Sensor A Circuit High Input (Bank 1)P0343 is a generic OBD-II powertrain diagnostic trouble code: Camshaft Position Sensor A Circuit High Input (Bank 1). It is logged by the engine control unit when the ckp/cmp monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0343 means
P0343 is set when the ECM detects that the Camshaft Position Sensor 'A' signal on Bank 1 is stuck at an abnormally high voltage — typically above 4.5 V — rather than switching between low and high as the cam reluctor teeth pass the sensor. For a Hall-effect sensor, this means the output is latched in its 'tooth-absent' state and never pulls low, which the ECM interprets as a continuous high or an open-circuit condition on the signal wire.
Common electrical causes include a short of the signal wire to the 5 V reference or battery voltage, a broken internal connection inside the sensor that defaults the output to the pulled-up reference, or a damaged reluctor wheel that provides no edges to trigger the sensor's switching. The result is similar in impact to P0342: the ECM loses reliable cam-phase information and must operate on a degraded synchronisation strategy.
Drivability effects range from extended crank time and rough idle to intermittent stalling. In many cases companion misfire codes (P0300–P030x) appear because fuel injection sequencing or variable valve timing control is impaired. Diagnosis should start with live signal voltage measurement before replacing any parts, as a short to reference voltage in the harness is easy to confirm with a multimeter.
Common causes
Most-frequently reported root causes when P0343 is logged.
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1
Faulty camshaft position sensor 'A' with internal short, defaulting the output to the high (reference) voltage level.
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2
Short circuit of the sensor signal wire to the 5 V reference supply wire within the harness.
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3
Short circuit of the signal wire to battery voltage (12 V), typically from damaged insulation in the harness.
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4
Damaged or missing teeth on the cam reluctor wheel, preventing the sensor from ever switching low.
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5
Loose timing chain or jumped timing causing the reluctor pattern to fall outside the ECM's expected range.
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6
Corroded connector with bridged pins connecting signal to reference voltage.
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7
Faulty ECM input channel (rare — only after wiring and sensor are confirmed good).
Symptoms drivers notice
How to diagnose P0343
A typical diagnostic flow when this code is present.
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1
Retrieve all stored codes and freeze-frame data; note any accompanying misfire or cam-crank correlation codes that suggest a mechanical issue.
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2
With the ignition on and engine off, measure voltage on the signal wire at the sensor connector — a reading near 5 V (or 12 V) with the sensor connected and engine not running is abnormal and indicates a short to voltage.
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3
Disconnect the sensor and re-measure the signal wire voltage; if it remains high, the short is in the wiring harness rather than the sensor itself.
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4
Inspect the full harness run from sensor to ECM for insulation damage, chafing on metal edges, or melted sections near heat sources.
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5
Check the cam reluctor wheel visually for broken, bent, or missing teeth if accessible — compare to manufacturer tooth-count specification.
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6
If wiring checks out and signal voltage collapses to near 0 V after sensor disconnection, replace the camshaft position sensor and retest.
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7
If the code persists, verify ECM reference voltage output and consider ECM diagnosis as a final step.
Related powertrain codes
- P000A — A Camshaft Position Slow Response Bank 1
- P000B — B Camshaft Position Slow Response Bank 1
- P000C — A Camshaft Position Slow Response Bank 2
- P000D — B Camshaft Position Slow Response Bank 2
- P0010 — A Camshaft Position Actuator Circuit (Bank 1)
- P0011 — A Camshaft Position - Timing Over-Advanced or System Performance (Bank 1)
Frequently asked questions
How is P0343 different from P0342?
Both indicate a camshaft position sensor signal outside the normal switching range. P0342 means the signal is stuck low (open circuit or short to ground), while P0343 means the signal is stuck high (short to reference or battery voltage, or a sensor whose output defaults high). The diagnostic approach differs: P0342 you look for opens and shorts to ground; P0343 you look for shorts to voltage.
Can the engine still run with P0343 active?
Often yes, using crank-only synchronisation. Some vehicles enter a limp mode that restricts RPM or disables variable valve timing. Hot restarts are frequently more affected than cold starts because the ECM's cam-sync strategy is more critical once normal operating parameters are established.
Could a weak battery trigger P0343?
It is possible but uncommon for a battery issue alone to cause a consistent P0343. Unstable supply voltage can produce false high readings in sensor circuits during cranking. If the code appears only during crank and disappears when the engine runs, test the battery and charging system before replacing the sensor.
Does a damaged reluctor wheel require engine disassembly to inspect?
Not always — on some engines the reluctor wheel is on the camshaft sprocket and can be viewed with the cam cover removed. In other designs it may require more access. Checking for a waveform with an oscilloscope on the signal wire during cranking is a non-invasive way to identify a reluctor problem before committing to disassembly.
Disabling P0343 in software
RaceTune can permanently disable P0343 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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