What causes fault code P0343?

• Most likely: Faulty Camshaft Position Sensor (internal short) • Likely: Open circuit in the sensor ground wire or corroded connector • Possible: Short to voltage on the signal return wire • Rare: Incorrect camshaft timing or stretched timing chain/belt • Rare: Internal Engine Control Unit (ECU) failure

How do you fix fault code P0343?

STEP 1: Inspect the sensor connector for corrosion or backed-out pins. Clean with contact cleaner if necessary. STEP 2: Verify power supply. With ignition ON (engine off), measure voltage between the reference and ground pins. Should be approx. 5V or 12V depending on manufacturer specs. STEP 3: Check ground circuit. Measure resistance between the sensor ground pin and chassis ground; it should be < 0.5 Ohms. STEP 4: Use an oscilloscope to back-probe the signal wire. Observe the waveform while cranking/running. If signal is stuck high despite good ground/power, replace sensor. STEP 5: Clear codes and perform a road test.

Powertrain (Engine & Gearbox)Standard EOBD

P0343 - Camshaft Position Sensor A Circuit High Input (Bank 1)

Q: What does fault code P0343 mean?

P0343 is triggered when the Engine Control Unit (ECU) detects a voltage signal from the Camshaft Position Sensor (CMP) 'A' that is higher than the calibrated range. Most modern CMP sensors are Hall-effect sensors producing a digital square wave. A 'Circuit High' condition typically suggests an open circuit on the ground side, a short to voltage on the signal wire, or an internal sensor failure. The ECU relies on this signal to determine cylinder #1 TDC for fuel injection timing and ignition synchronization. Loss of signal reliability often forces the ECU to revert to a fail-safe map using only the Crankshaft Position Sensor (CKP).

Q: What are the symptoms of fault code P0343?

• Check Engine Light (MIL) illuminated • Cranking for a long time before starting (hard start) • Engine stalling at idle or low speeds • Reduced engine power and poor fuel economy • Engine hesitation or jerking during acceleration

Last updated:1 February 2026

Related:Camshaft Position Sensor (CMP), Crankshaft Position Sensor (CKP), Engine Control Unit (ECU), Timing Belt/Chain, Wiring Harness

System

Powertrain (Engine & Gearbox)

Related Fault Codes

P0300

Random or Multiple Cylinder Misfire Detected

P0301

Cylinder 1 Misfire Detected

P0302

Cylinder 2 Misfire Detected

P0303

Cylinder 3 Misfire Detected

Technical Description

P0343 is triggered when the Engine Control Unit (ECU) detects a voltage signal from the Camshaft Position Sensor (CMP) 'A' that is higher than the calibrated range. Most modern CMP sensors are Hall-effect sensors producing a digital square wave. A 'Circuit High' condition typically suggests an open circuit on the ground side, a short to voltage on the signal wire, or an internal sensor failure. The ECU relies on this signal to determine cylinder #1 TDC for fuel injection timing and ignition synchronization. Loss of signal reliability often forces the ECU to revert to a fail-safe map using only the Crankshaft Position Sensor (CKP).

Possible Causes

Faulty Camshaft Position Sensor (internal short)

Open circuit in the sensor ground wire or corroded connector

Short to voltage on the signal return wire

Incorrect camshaft timing or stretched timing chain/belt

Internal Engine Control Unit (ECU) failure

Symptoms

Check Engine Light (MIL) illuminated

Cranking for a long time before starting (hard start)

Engine stalling at idle or low speeds

Reduced engine power and poor fuel economy

Engine hesitation or jerking during acceleration

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P0343 - Camshaft Position Sensor A Circuit High Input (Bank 1)

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P0343 - Camshaft Position Sensor A Circuit High Input (Bank 1)

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