What does cam sensor circuit high mean?

It means the ECU is reading a voltage on the cam sensor signal wire that is higher than design. This usually happens when the wire is broken, the sensor has failed open, or the wire has shorted to a 12 V source. The ECU cannot detect cam pulses, so the engine struggles to start or run.

Why does the engine eventually start but run badly?

Most modern ECUs have a backup mode that runs the engine on the crankshaft signal alone, with batch fuel injection instead of sequential. The engine starts but with degraded fuel efficiency, no VVT control, and reduced power.

Is P0343 always a sensor problem?

No. Wiring is just as common. Always test the wiring with the sensor unplugged before paying for a replacement sensor. A simple continuity check from the sensor connector to the ECU pin can save the cost of an unneeded sensor.

Can a recent cam cover service cause P0343?

Yes. Removing and reinstalling the cam cover can disturb the sensor harness, and an unseated connector or pinched wire is a common source of a sudden P0343 right after a service. Recheck connectors first.

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

Quick Answer

Not safe to drive

P0343 means the camshaft position sensor signal voltage is higher than the ECU expects. This usually happens when the signal wire is open (broken), the sensor coil has failed open, the connector has lost contact, or the signal wire has shorted to a 12 V power source. P0343 is the inverse of P0342 and points to wiring or sensor faults rather than mechanical timing problems.

Severity: Moderate · Ignition
Estimated repair cost: From €25 to €350+, varies by vehicle

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What does P0343 mean?

P0343 is a ignition-related diagnostic trouble code classified as moderate severity. When your vehicle's ECU detects this condition, it stores P0343 and illuminates the check engine light.

Where it is on the car

Crankshaft sprocket and position sensor
Timing chain or belt
Camshaft sprockets with VVT phasers
Camshaft position sensor
VVT oil control solenoid

What are the symptoms of P0343?

If your vehicle has triggered P0343, you may notice one or more of these symptoms:

Hard or extended cranking
Stalling shortly after start, especially when warm
Limp mode with reduced throttle response
Rough or surging idle
Check engine light on

What causes P0343?

Here are the most common causes of P0343:

Open circuit in the cam sensor signal wire
: high
Failed camshaft position sensor (coil open or internally damaged)
: high
Disconnected or backed-out sensor connector
: medium
Signal wire shorted to 12 V
: low
Oil contamination forcing the sensor open at the contacts
: low

Is it safe to drive with P0343?

No - address this immediately. The ECU sees voltage on the cam sensor signal that is above the expected range, typically because the circuit is open or shorted to power. Sequential injection and VVT are degraded, so hard starting and stalling are likely. Diagnose before extended driving.

How do you diagnose P0343?

Follow these steps to pinpoint the root cause of P0343:

Read freeze-frame data and confirm whether P0343 sets at cranking, at idle, or only after warm-up. Heat-soak-only failures often indicate a degrading sensor
Inspect the sensor connector for full seating and signs of oil or coolant intrusion
Unplug the sensor and check resistance across its terminals if magnetic, or verify 5 V reference and ground if Hall-effect. An infinite resistance reading confirms an open coil
Check continuity of the signal wire from the sensor connector to the ECU pin. An open in the wire produces P0343 even with a healthy sensor
With ignition on and sensor unplugged, measure voltage on each pin. A constant 12 V reading on the signal pin indicates a wire shorted to power

How much does P0343 cost to fix?

Repair costs for P0343 vary depending on the root cause and your vehicle. Here are typical estimates:

Repair	Parts Cost	Labor Cost	Total Estimate	DIY Difficulty
Reseat or replace sensor connector	€5–€30	€20–€80	€25–€110	Easy
Replace camshaft position sensor	€30–€150	€40–€200	€70–€350	Moderate
Repair wiring harness to camshaft sensor	€10–€50	€60–€200	€70–€250	Moderate

Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.

Full repair guides

Camshaft Position Sensor Replacement Cost

P0343 on specific vehicles

P0343 behaves differently depending on your vehicle. Select your car below for model-specific causes and known issues:

P0343 on BMW

BMW 3 Series

See BMW-specific causes & cost

P0343 on Volkswagen

Volkswagen Golf

See Volkswagen-specific causes & cost

P0343 on Audi

Audi A4

See Audi-specific causes & cost

Mercedes-Benz

Mercedes C-Class

2007-2024

M271 in the W204 C-Class is documented for cam sensor failures producing P0343 alongside related cam adjuster codes. The adjuster magnet and the sensor sit in the same oil and heat, so inspect both when either one fails. The job is professional-shop labour rather than DIY-friendly.

These codes are often seen alongside P0343 or indicate related issues:

Common questions about P0343

What does cam sensor circuit high mean?: It means the ECU is reading a voltage on the cam sensor signal wire that is higher than design. This usually happens when the wire is broken, the sensor has failed open, or the wire has shorted to a 12 V source. The ECU cannot detect cam pulses, so the engine struggles to start or run.
Why does the engine eventually start but run badly?: Most modern ECUs have a backup mode that runs the engine on the crankshaft signal alone, with batch fuel injection instead of sequential. The engine starts but with degraded fuel efficiency, no VVT control, and reduced power.
Is P0343 always a sensor problem?: No. Wiring is just as common. Always test the wiring with the sensor unplugged before paying for a replacement sensor. A simple continuity check from the sensor connector to the ECU pin can save the cost of an unneeded sensor.
Can a recent cam cover service cause P0343?: Yes. Removing and reinstalling the cam cover can disturb the sensor harness, and an unseated connector or pinched wire is a common source of a sudden P0343 right after a service. Recheck connectors first.

Read our detailed guides

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