What is the most common cause of P0340?

The most common cause of P0340 is a faulty camshaft position sensor (CMP) or issues in the sensor’s wiring or connector.

P0340 signals that the engine control module has detected a problem in the camshaft position sensor circuit. While faults can occur anywhere in the circuit, the sensor itself and its wiring are by far the most frequent culprits. Timing components and, in rarer cases, the ECU can also trigger the code, but the root cause often varies by vehicle make and model, so targeted diagnostics are essential.

What P0340 Means

P0340 is a diagnostic trouble code indicating a camshaft position sensor circuit malfunction or no valid signal from the CMP sensor. This sensor helps the engine timing system coordinate ignition and fuel injection. A failing sensor or circuit can cause symptoms such as rough idle, misfires, reduced power, or stalling, particularly at startup.

Scope and implications

In many vehicles, P0340 pertains to Bank 1 or Sensor A, but the exact labeling can differ by manufacturer. Because the camshaft position signal is critical for timing, a confirmed P0340 typically prompts inspection of the CMP sensor, its wiring, and the related timing components.

Most Common Causes

Below are the typical reasons P0340 appears on a scan. Each item highlights a source of a weak or absent camshaft signal in the CMP circuit.

• Faulty camshaft position sensor (CMP) itself


• Damaged, corroded, or loose wiring or connector in the CMP circuit


• Problems with the camshaft reluctor ring or timing components (timing belt/chain, sprockets, or guides)


• Insufficient power or poor ground to the CMP circuit


• PCM/ECU fault (less common, but possible)


• Oil leaks, contamination, or moisture affecting the sensor or connector

Diagnosing P0340 requires verifying the sensor signal, inspecting wiring and connectors, and checking timing components. In many cases, replacing the CMP sensor and repairing wiring resolves the code if the root cause is in the sensor circuit.

How to Diagnose

Practical steps a technician or a confident DIYer can take to identify the root cause of P0340.

1. Record the vehicle’s codes and freeze-frame data, then confirm P0340 with a second scan.


2. Visually inspect the CMP sensor, wiring, and connector for damage, oil leaks, corrosion, or loose connections; clean or reseat as needed.


3. Check the CMP sensor's power supply and ground. Verify the 5V reference (or manufacturer-specified reference) and ground continuity using a multimeter.


4. Measure the CMP signal directly (with the appropriate tool, such as a oscilloscope or a high-quality scan tool) while cranking or idling to assess waveform quality.


5. Inspect timing components (belt/chain, sprockets, and reluctor ring) for wear, misalignment, or damage that could cause an inconsistent signal.


6. Look for related codes (e.g., P0335, P0336 for crank sensor) that might indicate a broader timing/sensor issue.


7. Based on findings, replace the CMP sensor or repair wiring as indicated; re-test to confirm the code does not return.

Note: If you are not comfortable with electrical testing or timing checks, seek a qualified technician. Misdiagnosis can lead to unnecessary parts replacement or, in worst cases, engine damage.

Repair and Next Steps

Repair strategies typically focus on the CMP sensor and its circuit. Common steps include replacing a faulty sensor, repairing damaged wiring or connectors, addressing timing component wear, and ensuring proper grounding. After any repair, clear codes and perform a road test to confirm the issue is resolved and the code does not return.

Summary

P0340 most often points to the camshaft position sensor or its circuit—sensor failure, wiring or connector problems, timing component issues, or, less commonly, ECU faults. A systematic diagnostic approach centered on the CMP sensor, its wiring, and timing components is usually the quickest path to a durable fix.

How do I fix the engine code P0340?

To fix error code P0340, first use an OBD-II scanner to clear the code and see if it returns. If it does, inspect the camshaft position sensor (CMP) for physical damage and check that its wiring and connector are secure and free from corrosion or oil contamination. If the problem persists, use a multimeter to test the sensor's circuit for power, ground, and signal, or inspect the timing chain/belt and the engine's Engine Control Module (ECM). 
Step 1: Initial checks and clearing the code

• Use an OBD-II scanner: Connect a scanner to your car's diagnostic port, read all fault codes, and then clear the P0340 code. 
• Re-scan: Drive the vehicle and scan it again to see if the code reappears. If the code does not return, it may have been a temporary glitch. 

This video demonstrates how to clear error codes using an OBD-II scanner: 55s8020 AutomotiveYouTube · Sep 4, 2025
Step 2: Inspect the camshaft position sensor and wiring 

• Locate the sensor: The CMP is typically on the valve cover or cylinder head. 
• Check the connector: Ensure the electrical connector is securely plugged in and that the wires are not frayed, loose, or damaged. 
• Inspect for contamination: Look for signs of oil leakage on the sensor and its wiring, as this can cause a bad connection. Clean the sensor and connections with a suitable solvent if they are dirty. 
• Check the O-ring: When inspecting or replacing the sensor, make sure the O-ring is properly seated and has not fallen into the sensor hole. 

Step 3: Test the circuit and components 

• Check fuses: Locate and inspect the fuse for the CMP sensor to ensure it is not blown. 
• Test with a multimeter: 
  • Disconnect the sensor and use a multimeter to check the power, ground, and signal wires according to your vehicle's service manual. 
  • You can also perform a resistance test on the sensor itself with a multimeter, comparing the reading to the manufacturer's specifications. 
• Inspect the timing system: In some cases, a worn or loose timing chain or belt can trigger this code. Usually, other related codes will also be present in this situation. 
• Consider the ECM: If all other checks fail, the Engine Control Module (ECM) may be malfunctioning, though this is less common. 

This video shows how to use a multimeter to test the camshaft position sensor: 1mGerard BurkeYouTube · Jan 30, 2022
Step 4: Replace parts 

• Replace the sensor: If testing shows the sensor is faulty, replace it with a new one after making sure the new O-ring is in place. 
• Repair wiring: If you find damaged wires or connectors, repair or replace them. 
• Clear codes after repair: Once you have completed the repair, clear the fault codes again using the OBD-II scanner and take the vehicle for a test drive to confirm the issue is resolved. 

What can throw a camshaft position sensor code?

A camshaft position (CMP) sensor code can be caused by a faulty sensor itself, problems with the electrical circuit (like broken wires or loose connections), or issues with the engine's timing components. Other potential causes include a damaged reluctor wheel, engine sludge affecting the sensor, or a failing powertrain control module (PCM). 
Sensor and circuit issues

• Faulty sensor: The sensor itself can fail due to age, wear and tear, or internal damage from heat or debris. 
• Wiring and connection problems: This is a very common cause. Issues can include broken wires, short circuits, loose connections at the sensor or PCM, or a poor ground connection. 
• Damaged reluctor wheel: The CMP sensor reads a reluctor wheel, which is part of the camshaft. If this wheel is damaged or cracked, it can send incorrect signals. 

This video explains the symptoms and causes of a bad camshaft position sensor: 42sCar Care CluesYouTube · Nov 6, 2024
Engine and mechanical issues

• Engine timing problems: If the timing belt or chain has jumped a tooth, the camshaft will be out of sync with the crankshaft, which the sensor will detect. 
• Engine sludge: Oil sludge or metal debris circulating in the engine can interfere with the sensor's operation. 
• Internal engine damage: More serious internal damage to the camshaft itself can also cause a sensor code. 

You can watch this video to learn how to test the camshaft position sensor: 58sECU TESTINGYouTube · May 16, 2023
Other less common causes

• Faulty PCM: In some cases, the powertrain control module (the vehicle's computer) may be failing, though this is less common. 
• Starter/battery issues: Problems with the starting system or a weak battery can sometimes lead to a CMP sensor code. 

How to reset camshaft position sensor?

You don't "reset" a camshaft position sensor, but after replacement, many vehicles require a "relearn" procedure to recalibrate the new sensor to the engine. This can be done by driving the car or using a diagnostic scan tool to perform a "cam crank relearn," which is often necessary if the engine control module (ECM) hasn't automatically recognized the new sensor. For some cars, a scan tool is required, and the process involves starting the engine once the ignition is on and letting the system complete the relearn automatically, often after the engine reaches a specific temperature. 
Methods to perform a camshaft sensor relearn
1. Drive the vehicle 

• For some vehicles, the relearn procedure may happen automatically simply by driving the car. 
• Start by clearing any stored diagnostic trouble codes after replacement. 
• Drive the vehicle normally to allow the engine control module (ECM) to adapt to the new sensor. 

This video explains what to do after replacing a camshaft sensor: 1m Easy Car ElectricsYouTube · Jun 20, 2023
2. Use a diagnostic scan tool 

• This method is often required for modern vehicles and may be more reliable. 
• Connect a diagnostic scan tool to the vehicle's OBD-II port and turn the ignition on without starting the engine. 
• Navigate to the ECM's special functions menu and select the "cam crank relearn" or a similar function. 
• The tool will prompt you to start the engine and then monitor the relearn process, which can be completed automatically or require you to reach a specific temperature (e.g., 70∘C70 raised to the composed with power cap C70∘𝐶 or 158∘F158 raised to the composed with power cap F158∘𝐹). 
• Follow the on-screen instructions until the tool indicates the procedure is complete. 

What are the common mistakes when diagnosing P0340?

One common misconception with an error code P0340 is the source of the issue. While this error code deals with the camshaft position sensor, it can be caused by any electrical issue related to this sensor. This means that replacing your sensor may not be the right solution.