P0343 code: Camshaft Position Sensor A Circuit High
P0343 means camshaft Position Sensor A Circuit High. The code says where to look, not what failed — the fix depends on which cause your car actually has.
What P0343 means
The camshaft position sensor lets the computer know where the valvetrain is in its cycle so fuel injection and (on many engines) cylinder identification stay in sync with the crank. P0343 means the cam sensor's signal is reading HIGH — pegged at or above its expected maximum — the mirror image of P0342 (circuit low). The usual causes are a failed sensor, an open circuit or short to voltage in the wiring, or a corroded connector; a break in the circuit can leave the computer seeing a constant high level instead of the alternating pattern a spinning cam should produce. Symptoms match any lost cam signal: extended cranking, rough running, stalling, and on some engines a no-start — often intermittent and heat-related — so it belongs in the fix-promptly category.
P0343 symptoms
- Hard starting or extended cranking
- Stalling or rough running
- Hesitation and reduced power
- Occasional no-start on some engines
- Check-engine light
What it costs to fix P0343
Typical range: $80–$300 · about ~0.2–1 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| Camshaft position sensor | $30–$120 | ~0.2–1 hrs |
| Wiring / connector repair | $10–$120 | ~0.5–1.5 hrs |
Typically a quick, inexpensive job — cam sensors are cheap and usually accessible on the head or timing cover. Intermittent wiring faults are the wildcard that adds diagnostic time.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0343 for my exact vehicle →
How to fix P0343
Easy — basic tools, most owners can do this
- Work out which cam sensor is sensor A
On engines with more than one cam sensor, the standard convention makes A the intake cam (or the left or front one), and with no bank in the code it's the cylinder-1 bank or the only head. Confirm with a diagram before unplugging anything, because the intake and exhaust sensors on a dual-cam head often look identical.
- Inspect the connector for an open signal path
A signal terminal that has backed out, spread, or corroded behaves like a cut wire, and with the circuit open the computer's pull-up shows as a constant high. Unplug sensor A, look into both halves for green corrosion, oil residue, and a pin sitting lower than its neighbours, then clean it, reseat it, and click the lock home.
- Check reference, ground, and pull-up at the harness
Back-probe with the key on. Expect the reference the service manual lists (often 5 volts, sometimes battery voltage), a ground with almost no voltage drop, and, with the sensor unplugged, the computer's pull-up on the signal pin. Battery voltage on a 5-volt signal wire means a short to power; nothing at all means an open between the connector and the computer.
- Turn the engine slowly and watch the signal switch
With the sensor plugged in and back-probed, rotate the crank by hand with a socket on the pulley bolt and watch a multimeter on the signal wire. A healthy Hall-type sensor snaps between near zero and near the pull-up voltage as each target tooth passes; a reading that never drops, with good feed and ground, means the sensor has failed.
- Replace sensor A and check the reluctor if it returns
Most cam sensors are held by a single fastener; seat the new one with its seal lightly oiled and never hammer it into the bore. If P0343 comes back with a new sensor and sound wiring, have the cam reluctor and the computer's input checked — both are uncommon causes that need a scope and some teardown to confirm.
DIY or shop? This sits at the easy end of engine electrical work: the cam sensor is usually on top of or at the front of the head, the checks need only a multimeter and a wiring diagram, and the sensor itself is a short swap. It becomes shop work when the short or open is buried deep in the engine harness, when the sensor is hidden behind other components, or when a new sensor doesn't fix it and the reluctor or computer needs scope diagnosis. If the engine has stalled, avoid driving it there.
Tools for the DIY steps: Digital multimeter · Back-probe pins · Wiring diagram · Socket set · Electrical contact cleaner · Breaker bar or ratchet to turn the crank by hand
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for P0343.
Start a case with P0343 and your car. Redline weighs these causes against what your car shows, and names the check that would settle it before you buy parts.
Can I drive with P0343?
Redline can’t determine from a symptom or code alone whether your car is safe to drive.
P0343: common questions
What's the difference between P0343 and P0342?
Direction of the fault. P0342 means the cam sensor's signal is stuck low (dead sensor or short to ground); P0343 means it's stuck high (open circuit, short to voltage, or failed sensor). The diagnosis path — connector, wiring, then sensor — is the same.
Why won't my car start sometimes, then starts fine?
Intermittent cam-sensor faults are classic for this — a marginal sensor or connection drops out with heat or vibration, causing a random no-start or long crank, then works again. If P0343 is stored alongside that behavior, the cam sensor circuit is the prime suspect.
Can I drive with P0343?
That can't be judged from a code alone. Many engines fall back on the crank sensor, but stalling and no-starts are the real risk. Get it diagnosed promptly rather than waiting for it to strand you, and if it stalls or won't restart reliably, stop driving it and have it towed.
How much does it cost to fix P0343?
Usually inexpensive — the sensor is a cheap part and typically takes well under an hour to replace. If the fault is in the wiring instead, cost depends on how long the break takes to find.
Related trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P0343 from your phone. See our guide to the best OBD2 Bluetooth adapters. Run a repair shop? See Redline for shops.
Generic OBD-II reference. Manufacturer-specific behavior varies. Confirm with a scan tool and, for safety-related codes, a professional inspection. Cost ranges are reference ranges, not quotes.
Seeing P0343 on your car?
Every problem becomes a Case. Tell Redline what the car is doing: it shows what the evidence supports, what’s still missing, and what to check next, before you approve a repair.
“Inner pad ~1 mm. Outer pad 3 mm.”
Next: check the slide pins move freely before buying parts.