P0340 Code: Camshaft Position Sensor A Circuit Malfunction — Bank 1
Last reviewed May 2026 · Reviewed by the Find This Code Editorial Team
Quick Answer
The camshaft position sensor on Bank 1 isn't sending a reliable signal to the ECU.
At a Glance
What this code means
The camshaft position sensor (CMP) tells the ECU the position of the camshaft so it knows which cylinder is in its intake stroke and when to fire fuel injectors in the correct sequence. P0340 means the CMP signal is absent or erratic on Bank 1. Unlike the crankshaft position sensor (CKP), a failed CMP sensor may still allow the engine to run (in a degraded mode) but will cause starting problems and poor performance.
Common causes
- Failed camshaft position sensor
- Damaged CMP sensor wiring or connector
- Reluctor wheel damage on the camshaft
- Timing chain stretch or jump causing an implausible cam position signal
- Oil contamination of the sensor (common when oil is leaking near it)
Symptoms you might notice
- Hard starting or extended cranking before start
- Check engine light on
- Rough running or stalling
- Reduced performance
- May illuminate alongside CKP or timing-related codes
Can you still drive?
With caution if the engine is running. If hard starting is the main symptom, you risk being stranded.
How serious is this code?
High. A faulty CMP sensor can cause no-start conditions and generally poor engine management.
Before you replace parts
Parts replacement is often not the first step. Before buying anything, it's worth checking these basics:
- Check the CMP sensor area for oil leaks — oil contamination of the connector causes sensor failures and replacing the sensor without fixing the leak will result in the same code returning
- Look for companion timing chain codes — P0340 alongside codes about camshaft timing or chain performance may indicate a bigger engine issue
How to troubleshoot it
- Inspect the CMP sensor connector for oil contamination or corrosion
- Check the wiring harness from the sensor to the ECU for chafing or damage
- Test the sensor's resistance and output voltage with a multimeter
- Check for timing chain codes alongside P0340 — a stretched timing chain can cause cam position errors
- Replace the CMP sensor if wiring is intact but the signal is absent or erratic
Common mistakes to avoid
These are the most frequent diagnostic errors when dealing with P0340. Avoiding them can save time and money.
- Replacing the camshaft position sensor without first inspecting the timing chain or belt for stretch or damage
- Not checking the sensor's reference voltage and ground at the connector before condemning the sensor
- Ignoring wiring routing near hot engine components that can melt or damage the cam sensor wiring harness
- Replacing the sensor on a timing-chain engine without also inspecting the chain tensioner
Tools that may help
These are the types of tools commonly used when diagnosing this code. Having the right tool can save time and help confirm a diagnosis before spending money on parts.
- OBD-II scanner
- Multimeter
- Oil pressure gauge (if timing chain wear is suspected)
Estimated repair cost range
CMP sensor replacement: $30–$150 for the part. Labor: $50–$200 depending on sensor location.
Costs vary significantly by vehicle, location, and whether you use OEM or aftermarket parts. These are general ranges for reference only.
When to call a mechanic
If you've completed the basic troubleshooting steps and the code keeps returning, or if you don't have access to the proper diagnostic tools, it's worth consulting a professional. A qualified technician can perform a full diagnosis and confirm the root cause before any parts are purchased. When in doubt, get a professional opinion — it can save you from an expensive misdiagnosis.
Real-world note
On many engine designs, the CMP sensor sits directly above a cam journal and is vulnerable to oil leaks from nearby seals. If the sensor connector shows oil contamination, fix the oil leak first — otherwise the new sensor will fail the same way.
Learn more
How we write these guides
Find This Code guides are written based on OBD-II specification documentation, established automotive diagnostic practices, and real-world patterns observed across vehicle makes and models. Content is reviewed for accuracy and plain-English clarity before publication. Pages are marked with a “Last reviewed” date and updated when diagnostic guidance or code interpretation changes. All content is educational — it is not a substitute for hands-on diagnosis by a qualified mechanic.
Last reviewed May 2026 · Find This Code Editorial Team · Editorial standards →
Sources & references
Our guides are written based on OBD-II specifications, automotive engineering principles, and established diagnostic best practices. Key reference sources include:
- U.S. EPA — On-Board Diagnostics (OBD)Official EPA documentation on OBD-II standards and emissions monitoring requirements for passenger vehicles.
- ASE — Automotive Service ExcellenceIndustry certification body for automotive technicians; sets best-practice diagnostic and repair standards.
Informational purposes only. This guide is for educational reference and is not a substitute for diagnosis by a qualified technician. Repair costs, causes, and symptoms may vary by vehicle make, model, year, and condition. Always consult a licensed mechanic before performing major repairs.