P0340 Code Explained: Camshaft Position Sensor Circuit Malfunction (Full Diagnostic Guide)

P0340 – Camshaft Position Sensor Circuit Malfunction

This code means the engine control module (ECM) is not receiving a proper signal from the camshaft position sensor (CMP).

The camshaft sensor tells the computer:

• which cylinder is firing

• valve timing position

• fuel injection timing

• ignition timing

Without this signal, the engine may run poorly — or not start at all.

🔬 What the Camshaft Position Sensor Does

The CMP sensor works together with:

• crankshaft position sensor (CKP)

• ignition system

• fuel injectors

The ECM compares crankshaft and camshaft signals to determine proper engine timing.

If the camshaft signal:

• disappears

• becomes unstable

• or falls outside expected range

P0340 is triggered.

⚠ Why P0340 Can Be Serious

Symptoms may include:

• hard starting

• extended cranking

• engine stalling

• rough idle

• loss of power

• misfire codes

In some vehicles, the engine may enter limp mode.

If timing is involved, the issue can become serious.

🔎 Most Common Causes of P0340

1️⃣ Faulty Camshaft Position Sensor (Very Common)

Internal failure due to:

• heat

• oil contamination

• age

Sensor replacement often fixes the issue — but not always.

2️⃣ Damaged Wiring or Connector

Common problems:

• broken wires

• oil-soaked connector

• corrosion

• loose connection

Intermittent wiring faults can cause random stalling.

3️⃣ Crankshaft Position Sensor Issues (Related)

If crank sensor fails:

• timing sync is lost

• ECM may log camshaft-related codes

Always check both sensors.

4️⃣ Timing Chain / Belt Problems

If timing chain stretches:

• cam timing becomes inconsistent

• sensor signals fall out of sync

This may also trigger:

• P0016

• P0017

👉P0017 Code – Crankshaft Position / Camshaft Position Correlation (Bank 1 Sensor B) | Meaning, Causes & Fix

👉P0016 Code – Crankshaft Position / Camshaft Position Correlation (Bank 1 Sensor A) | Meaning, Causes, Symptoms & Fix

5️⃣ Low Engine Oil or VVT Problems

On VVT engines:

• oil pressure affects cam timing

• dirty oil can delay cam response

Sometimes an oil change resolves early symptoms.

⚙️ Professional Diagnostic Process

Step 1: Check for Related Codes

Look for:

• P0335 (crankshaft sensor)

• P0016 (cam/crank correlation)

• misfire codes

Clusters matter.

Step 2: Inspect Wiring First

Visual inspection can save money.

Check:

• melted insulation

• oil contamination

• damaged pins

Step 3: Monitor Live Camshaft Data

With scanner:

• verify camshaft RPM signal

• compare with crankshaft signal

• check for dropouts

Advanced shops may use an oscilloscope for waveform testing.

Step 4: Check Mechanical Timing (If Needed)

If sensor and wiring test good:

• inspect timing chain alignment

• check for stretched chain

• listen for rattling noise on cold start

Mechanical timing issues require immediate attention.

🚨 Symptoms of P0340

• engine cranks but won’t start

• rough idle

• hesitation

• stalling

• check engine light

• reduced fuel economy

Some cars may still run normally at first.

💰 Repair Costs

• Camshaft position sensor: $100–300

• Wiring repair: $100–400

• Crankshaft sensor: $150–400

• Timing chain repair: $800–2500+

Cost depends heavily on root cause.

❌ Common Misdiagnosis Mistakes

• Replacing sensor without checking wiring

• Ignoring crankshaft sensor

• Not checking oil level

• Replacing timing chain without confirming

• Clearing code without monitoring live data

📊 Quick Diagnosis Table

FAQ

Is P0340 serious?

It can be, especially if timing issues are involved.

Can I drive with P0340?

Short-term yes, but stalling risk exists.

Does P0340 mean the sensor is bad?

Not always — wiring and timing issues are common.

How long does a camshaft sensor last?

Typically 80,000–150,000 miles.

Final Thoughts

P0340 indicates a camshaft position sensor circuit issue — but diagnosis must go beyond replacing the sensor.

Correct approach:

➡ Inspect wiring
➡ Check for related codes
➡ Monitor live timing data
➡ Verify mechanical timing

Accurate diagnosis prevents unnecessary timing chain repairs.