P0343

A trouble code records what a control module measured. It does not identify which part failed. Test before replacing anything.

Safe to drive

Treat as unsafe for anything beyond a short trip to get it repaired. Extended cranking, stalling in traffic, and a failure to restart are all realistic. If it has already stalled on you or cranks a long time before firing, tow it rather than driving on.

Urgency

Get it looked at now

Will it pass emissions

No

If ignored

Expect the intermittent stall and long-crank behaviour to worsen until the engine will not start. With variable valve timing disabled the engine runs on a fallback strategy that costs power and fuel economy. Prolonged crank-only synchronization can also drive fuel delivery into a batch-fire fallback, which increases emissions and can foul plugs over time.

Check engine light

Solid

Clearing the light

A completed drive cycle is normally required before the monitor re-runs and the light can clear.

• Power loss especially in mid-rpm range
• Possible rough idle or stalling
• Increased fuel consumption

Many vehicles show no symptom at all beyond the warning light. The absence of a symptom does not mean the fault is not real.

These are the causes this code can have. For the order to work through them in, see what to check first.

Ordering reflects how often each cause is responsible in general, not a probability for your vehicle. Confirm by testing.

In order. Each of these is cheaper or faster than what follows it, and each one can make the rest unnecessary.

1. The sensor ground circuit specifically, not just the signal wire

   An open ground on a Hall-effect sensor leaves the pulled-up signal line stuck high and produces this exact code. It is the cause most often missed, and testing it costs one voltage-drop reading.

2. Sensor connector condition — oil, corrosion, spread or backed-out terminals

   Cam sensors sit in oily, hot locations. A backed-out ground terminal is a classic cause and is invisible unless you pull the connector apart and inspect the pins.

3. Freeze frame and whether the fault is hot, cold, or over bumps

   Heat-dependent behaviour points at the sensor itself. Bump-dependent behaviour points at the harness or connector.

4. Whether crankshaft position codes are also stored

   Both together suggest a shared circuit problem, a shared ground, or a timing chain or belt issue rather than a single sensor.

5. Engine oil level, condition, and whether oil is wicking into the sensor connector

   Oil migrating up the harness from a failed sensor O-ring contaminates the connector and causes signal faults, and it also tells you the sensor seal has failed.

1. Record freeze frame and characterize the symptom

   Tools Scan tool

   Note whether the code sets during cranking, at idle, at a specific RPM, or during a stall. Note how long the engine cranks before starting. Then try to reproduce it consistently.

   Expected

   A repeatable trigger condition

2. Verify reference voltage and ground quality at the sensor connector

   Tools DMM, wiring diagram

   With the key on and the sensor disconnected, confirm the PCM is supplying reference voltage on the supply pin — commonly a regulated 5 volts or system voltage depending on design, and which one your vehicle uses is vehicle-specific. Then test the ground: with the sensor reconnected and the circuit live, measure voltage drop from the sensor ground pin to battery negative — under about 0.1 V is good. If you prefer a resistance check, turn the key off first and measure with the circuit unpowered; under about an ohm. A missing or high-resistance ground is the finding. Do this before anything else — it is the fastest path to the most-missed cause.

   Expected

   Specified reference voltage present, and a ground showing under about 0.1 V drop live, or under about an ohm measured with the circuit unpowered

3. Scope the cam signal at the sensor connector while cranking

   Tools Oscilloscope, back-probe leads

   Back-probe the signal line with the sensor connected and crank the engine. A Hall-effect sensor should produce a clean square wave switching from near reference voltage to near zero. A signal that never leaves the high rail confirms the fault is at or before this point.

   Expected

   A square wave with clean transitions to near zero volts, repeating in step with camshaft rotation

4. Check the signal conductor for a short to voltage

   Tools DMM, wiring diagram

   Disconnect both the sensor and the PCM connector. With the key on, measure voltage on the isolated signal conductor. Any voltage present means the wire is contacting a powered circuit somewhere in its run.

   Expected

   No voltage on the isolated conductor

5. Test harness continuity, resistance, and intermittents

   Tools DMM, wiring diagram, oscilloscope

   With the circuit unpowered and both ends disconnected, measure each conductor end to end for continuity and excessive resistance, and check for shorts between conductors. Then reconnect and wiggle-test the full harness run while monitoring a live voltage drop or the scoped signal, since a high-resistance ground under vibration is a common intermittent that a static resistance check will not catch.

   Expected

   Continuity on each conductor with minimal resistance and no change during the wiggle test

6. Substitute a known-good sensor and re-scope

   Tools Hand tools, oscilloscope

   If reference voltage and ground are confirmed present and the signal line is not shorted to voltage, the sensor itself is the remaining candidate. Verify with a good part rather than assuming, and inspect the removed sensor's O-ring for oil leakage.

   Expected

   A correct square wave appears with the substituted sensor

7. Inspect the camshaft trigger wheel and check cam-to-crank timing

   Tools Two-channel oscilloscope, borescope, hand tools

   If the sensor and wiring are good, look at what the sensor reads — a trigger wheel that is damaged, loose on the camshaft, or mispositioned. Capture crank and cam on a dual-trace scope and confirm their phase relationship is stable, which also screens for timing chain stretch.

   Expected

   An undamaged, securely mounted trigger wheel and a stable crank-to-cam phase relationship

8. Consider the PCM only after everything upstream is proven

   Tools Oscilloscope, DMM, wiring diagram

   If a correct signal reaches the PCM connector, reference voltage and ground are correct, and PCM power and grounds are verified, the input circuit inside the module is the remaining candidate.

   Expected

   All upstream circuits verified good with the fault still present

US independent-shop ranges, parts plus labour. Sensor cost is modest and many are accessible in under an hour, but some sit behind the timing cover or under the intake and cost several times that in labour. Wiring repairs are usually cheaper than the parts they save. Module replacement typically requires programming and sometimes an immobilizer relearn, adding labour or a dealer visit.

• Replacing the cam sensor without checking its ground circuit, when an open ground produces an identical stuck-high signal.
• Measuring resistance on a circuit that is still powered. The meter's own test current competes with circuit voltage, the reading is meaningless, and the meter can be damaged. Test a live ground by voltage drop, or turn the key off before reaching for the ohms range.
• Passing a ground on a resistance check that then fails under load. A corroded connection can read low on ohms and still drop excessive voltage when it has to carry current.
• Assuming the sensor's location or connector pinout from another vehicle. Both vary by make, model, and engine.
• Overlooking oil that has wicked into the connector through a failed sensor O-ring, then installing a new sensor into a contaminated connector.
• Ignoring a simultaneously stored crank sensor code, which usually means a shared circuit or a timing chain problem rather than a cam sensor.
• Condemning the PCM without first verifying its own power and ground circuits, which mimic module failure when degraded.

• Camshaft Position Sensor
• Camshaft Position Sensor Wiring

• P0340Camshaft Position Sensor "A" Circuit (Bank 1 or Single Sensor)Severity level 3 of 5: Diagnose soon.moderate
• P0342Camshaft Position Sensor "A" Circuit Low Input (Bank 1)Severity level 3 of 5: Diagnose soon.moderate
• P0344Camshaft Position Sensor A Circuit Intermittent (Bank 1 or Single Sensor)Severity level 3 of 5: Diagnose soon.moderate

Definition

Generic code set (SAE J2012 / ISO 15031-6) via the OBDexopen database, dedicated to the public domain under CC0-1.0.

Diagnostic guidance

Written and reviewed in-house. See our editorial policy.

Review status

Reviewed

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