P0343 Code: Camshaft Position Sensor A Circuit High (Bank 1)
The bank 1 cam signal is stuck high: an unlatched connector, broken ground or open wire after nearby work.
At a glance
Severity: Moderate
- Meaning
- Camshaft Position Sensor A Circuit High (Bank 1)
- System
- Ignition & Misfire · Powertrain
- Safe to drive?
- With caution
- Typical repair cost
- $0–$380
- DIY difficulty
- Easy
The computer supplies the high level on the cam signal line through a pull-up resistor, and a working Hall sensor pulls it low each time a target window passes. P0343 means the bank 1 sensor A line stayed above the high threshold instead of switching, so the computer saw no usable cam edges. Anything that stops the sensor from pulling down produces this: a lost ground, a lost supply, a break in the wire between sensor and computer, or a sensor whose output stage has died. Oil that has crept into the connector can also bridge the supply pin to the signal pin. Because the cam sensor on many engines sits right next to the coils and valve cover, P0343 very often shows up shortly after spark plug, coil or valve cover gasket work.
Can I keep driving? Usually safe to drive short distances if the engine starts and runs smoothly, with longer cranking and reduced power. If it set right after work under the hood, check the connector before driving anywhere, as the fix may take seconds.
How to read P0343
- P Powertrain
- 0 Generic (SAE)
- 3 Ignition / misfire
- 43 Specific fault
Symptoms
- Check-engine light shortly after spark plug, coil or valve cover work
- Longer cranking than before, sometimes a hesitant first start
- Less power and a flatter throttle response with VVT disabled
- Other 'high' sensor codes if a shared sensor ground has opened
- Occasional stall or no-restart when the engine is hot
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Connector not fully latched or a terminal pushed back after nearby work
- Open sensor ground or shared sensor return circuit
- Cam sensor output failed open internally
- Signal wire broken at a flex point near the head or pulled from its terminal
- Oil in the connector bridging the supply pin to the signal pin
- Signal wire shorted to a 12-volt circuit, such as a coil feed
- Engine computer input fault
Diagnosis step by step
Check the connector first if work was done nearby
Push the connector firmly home until the lock clicks, then pull gently to confirm it holds. Look into it for a terminal sitting lower than its neighbors. Clear the code and restart; if the engine now starts quickly, you're done.
Tools: Flashlight
Back-probe the signal with the sensor connected
Key on, engine off, turn the crank slowly by hand and watch the signal wire at the sensor. A steady 5 volts that never drops means the sensor isn't switching. A steady 11 to 14 volts means the signal wire is touching a 12-volt feed, often a coil supply in the same loom.
Tools: Multimeter, Torque wrench
Voltage-drop test the ground
Measure between the sensor's ground pin (back-probed) and battery negative while cranking. Anything above about 0.1 volt means a poor ground. If MAP or throttle position 'high' codes are also stored, suspect the shared sensor ground back at the computer or a common splice.
Tools: Multimeter
Compare the sensor end with the computer end
If the sensor switches correctly at its own connector but the computer still sees a constant high, the signal wire is open between them. Measure end-to-end continuity with the battery disconnected, flexing the harness where it moves with the engine.
Tools: Multimeter
Look for oil between pins
Oil in a cam sensor connector means its O-ring or body seal is leaking. Clean the connector with electrical contact cleaner, let it dry, fit a new sensor with a new O-ring and check that the oil hasn't travelled further along the harness.
Tools: Screwdriver, Flashlight
Replace and confirm the fix
If supply and ground are good and the sensor never pulls the line low, replace it. Confirm on the scan tool that cam and crank are synchronized and that hot and cold starts are quick again.
Tools: OBD-II scanner
Where the parts are
- 1Ignition coil
- 2Spark plug
- 3Fuel injector
- 4Camshaft sensor
- 5Crankshaft sensor
- 6Engine computer (ECM)
- 7Intake manifold
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Reseat connector or re-pin a pushed-back terminal | Yes | $0–$120 |
| Replace camshaft position sensor and O-ring | Yes | $90–$280 |
| Repair open ground or broken signal wire | No | $100–$380 |
| Clean oil from connector and replace leaking sensor | Yes | $120–$320 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Emissions / smog test impact
Will fail
A stored P0343 with the check-engine light on fails a state OBD emissions test. After reseating or replacing parts, clear the code and drive normally for a few days so the monitors can complete before the test.
Frequently asked questions
I just changed my spark plugs and now have P0343. What happened?
On many engines the cam sensor connector sits right beside the coils, and it's easy to knock it loose, crack its lock or tug a wire out of its terminal. Reseat it and check for damage before assuming the sensor failed.
What does 'circuit high' mean for a Hall sensor?
The computer provides the high level; the sensor only pulls it low. If the line is stuck high, the sensor isn't pulling it down, which usually means it has lost ground or supply, the wire is broken, or the sensor's output has failed.
Why is there oil in my cam sensor connector?
The sensor is sealed into the head or timing cover with an O-ring. When that ages, pressurized oil seeps past and can travel through the sensor body into the connector. It can bridge pins and eventually wick along the harness, so replace the sensor and clean the connector.
Can I drive with P0343?
Most engines run on crank signal alone in a backup mode, so short trips are usually possible. Expect slower starts and less power, and fix it soon, because a combined crank fault would leave the engine unable to start.