P0340

P0340: Camshaft Position Sensor Circuit Malfunction (Bank 1) — Causes, Fixes & Cost

P0340 means the ECU detected a problem with the camshaft position sensor (CMP) circuit on Bank 1. The CMP sensor tells the ECU exactly where the camshaft is in its rotation cycle — critical information for precise fuel injection timing and ignition sequencing. When this signal is missing or erratic, the ECU can't determine the correct injection timing, which causes hard no-start, random stalling, or severe hesitation. P0340 is a high-urgency code because it directly causes no-start conditions and can leave you stranded. The sensor itself is often the culprit, but damaged wiring or a failing reluctor wheel (tone ring) on the camshaft can also trigger it.

🔧 Common Causes

Failed camshaft position sensor (most common)
Damaged, corroded, or shorted sensor wiring harness
Poor connection at the CMP sensor connector
Damaged reluctor wheel (tone ring) on the camshaft
Timing chain stretched or jumped (sensor signal out of sync)
Failed crankshaft position sensor affecting correlation (rare)

⚠️ Symptoms You'll Notice

Check Engine Light on
Engine cranks but won't start (or very hard to start)
Engine stalls randomly, especially at idle or low speed
Rough running and severe hesitation under acceleration
Engine misfires with no specific cylinder pattern
Poor fuel economy (ECU using backup fuel timing maps)

Estimated Repair Cost

DIY Cost

$15–$80 (camshaft position sensor)

Parts only

Shop Cost

$150–$400 (sensor replacement + labor)

Parts + labor

DIY Fix Path — Cheapest First

Work through these in order. Most people fix it by step 2.

1

Replace the Camshaft Position Sensor

$15–$80

This is the most common fix for P0340. CMP sensors are plug-and-play replacements on most vehicles — one bolt, one connector. Buy OEM or a quality aftermarket sensor (Delphi, Bosch, Standard Motor Products). Cheap generic sensors sometimes trigger the code again within weeks. Job takes 15–30 minutes on most engines.
2

Inspect CMP Sensor Wiring & Connector

$0–$20

Before replacing the sensor, check the 2-3 pin connector for corrosion, bent pins, or backed-out terminals. The CMP sensor lives near the timing cover and is exposed to oil and heat — connector failures are common. Spray contact cleaner on the connector and reseat it. A corroded connector cleaned for free can save an $80 sensor replacement.
3

Inspect the Reluctor Wheel

$0

With the sensor removed, look into the sensor bore and inspect the tone ring (reluctor wheel) on the camshaft. A missing or cracked tooth, or heavy buildup of metallic debris, will cause an erratic signal. If the ring is damaged, it's a more significant repair (requires timing cover removal), but rule this out before assuming sensor failure.
4

Check Timing Chain Stretch

$0–$50 diagnostic

If you also have timing-related codes (P0016, P0017) alongside P0340, a stretched timing chain may be shifting cam timing enough to confuse the sensor. At a shop, they can use live data to check cam/crank correlation. A worn timing chain is a significant repair ($400–$1,200), but catching it before it jumps teeth prevents catastrophic engine damage.

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Frequently Asked Questions

Can P0340 cause a no-start?

Yes — this is one of the most common causes. Without a valid camshaft position signal, the ECU defaults to sequential injection mode or may refuse to start entirely on some vehicles. If your engine cranks but won't fire, and P0340 is stored, replace the CMP sensor first.

What's the difference between P0340 and P0335?

P0340 is a camshaft position sensor circuit fault. P0335 is a crankshaft position sensor circuit fault. Both can cause similar symptoms (no-start, stall) because both sensors feed the ECU timing information. P0340 specifically relates to the CAM sensor; P0335 relates to the CRANK sensor. Some vehicles need both signals to run.

Is P0340 an emergency?

Yes, if it's causing a no-start or stalling — you could be stranded. Even if the car is running, an intermittent CMP signal means sudden stalling at any time (including on the highway). Treat P0340 as urgent and fix it before relying on the vehicle for important trips.

Can I drive with P0340?

Not recommended for more than a very short distance. If the car starts, the CMP sensor signal is currently working — but it may be intermittent, and the engine can stall without warning. At a minimum, carry a replacement CMP sensor (they're cheap) and fix it as soon as possible.