📋 Quick Facts
Time
20-60 min
Difficulty
Easy
Tools
6 needed
Cost to DIY
$40-220
The camshaft position sensor (CMP) tells the ECU which stroke each cylinder is in - critical for sequential fuel injection and coil-on-plug ignition timing. Symptoms: P0340/P0341/P0345, long crank time, rough idle, stalling, intermittent no-start. Usually located on the front or rear of the cylinder head, secured with a single bolt.
🛠 What You'll Need
- New CMP sensor (match part number) (camshaft position sensor on Amazon)
- Metric socket set (8-13mm) (metric socket set on Amazon)
- Torx and hex bit set (Torx and hex bit set on Amazon)
- Multimeter (verify signal) (multimeter on Amazon)
- OBD-II scanner (clear codes after) (OBD-II scanner on Amazon)
- Engine oil (lube new O-ring) (engine oil on Amazon)
⚠ When NOT to DIY thisIf the CMP is buried under the timing cover or behind a chain tensioner, the job becomes a half-day repair - leave it to a shop. Also, if you have multiple cam sensors (DOHC engines often have 2-4) and codes for several, the issue is usually wiring or VVT system, not all sensors failing at once.
🔌 Expected Electrical ReadingsHall-effect CMP: 5V or 12V reference, signal pulses 0V to reference voltage as the cam tone wheel rotates. With key on, engine off: signal should be at one rail (0V or full ref). Cranking: should pulse between rails. Stuck at one voltage = bad sensor.
✅ Before You Start - Checklist
- Park on level, solid ground (no slopes, no soft dirt)
- Engine is at the correct temperature (cold or warm as specified)
- All tools and parts on hand BEFORE you begin
- Owner's manual nearby for torque specs and locations
- Safety: gloves, eye protection, hood propped open
📝 Step-by-Step Instructions
- Disconnect the negative battery terminal60 seconds to reset ECU adaptive values.
- Locate the CMP sensorMost commonly: front of the cylinder head near the camshaft pulley, OR rear of the head near the firewall. Look for a small black plastic sensor with a 2-3 pin connector secured by one bolt.
- Photograph wire routing and connector orientationOn engines with multiple cam sensors, plugs can be swapped - this prevents reinstall mistakes.
- Unplug the electrical connectorPress the tab, pull straight off. Pins are small - do not twist.
- Remove the mounting boltUsually a single 8mm or 10mm bolt or Torx T30. Some are tucked under hoses - move them aside without disconnecting.
- Pull the old sensor outTwist 1/4 turn and pull. If stuck, the O-ring is glued by heat - wiggle gently.
- Inspect the boreShould be clean. Metal shavings indicate cam reluctor wheel damage - stop and have a mechanic inspect before installing the new sensor.
- Lube the new O-ring with clean engine oilDry O-rings tear on installation, causing oil leaks.
- Install the new sensorPush straight in until fully seated, then thread the bolt by hand. Torque to spec (typically 5-8 ft-lb - small bolt, plastic-body sensor).
- Reconnect the electrical connectorPush until it clicks. Verify any wire routing matches the photo.
- Reconnect the battery negativeSnug the clamp.
- Start and verifyEngine should start within 1-2 cranks. Long crank time after replacement usually means wrong part or loose connector.
- Clear codes and test driveDrive 15 minutes mixed conditions. Watch for the check engine light. Adaptive timing relearn takes 50-100 miles.
✅ After You Finish - Verify Checklist
- No tools left in the engine bay or under the car
- Test the system you worked on (start, drive, check, etc.)
- Look for leaks or drips after 5 minutes of running
- Record the date and mileage in your service log
- Recycle or properly dispose of any old parts/fluids
🔗 Related Guides
❓ Frequently Asked Questions
Will a bad cam sensor cause a no-start?
On many engines yes - the ECU needs CMP to fire sequential injectors. On others (especially older OBD-II), the engine will start in batch-fire mode but run poorly. P0340 plus a no-start usually means the cam sensor.
Cam sensor vs crank sensor - which is more critical?
Crank (CKP) is more critical - most engines will not start without it. Cam (CMP) failure usually causes hard start or stalling, not a hard no-start.
Why is my engine running rough after replacing the CMP?
Three causes: (1) wrong sensor (CMP and CKP look identical on some engines), (2) loose connector, (3) you need to do a cam-crank correlation relearn (some Chrysler and GM vehicles). Bidirectional scanner needed for the relearn.
Can I clean the CMP instead of replacing?
Sometimes oil sludge on the sensor tip can cause weak signal. Remove, wipe with carb cleaner, reinstall. If symptoms return within a week, replace.
Why do I have a CMP code after replacing the timing belt?
Most common: the new belt slipped a tooth or the cam is one tooth off. Recheck timing marks before throwing a new sensor at it.
Do all engines have a CMP sensor?
Yes for any OBD-II engine (1996+ US). DOHC engines often have one per camshaft (2-4 total). VVT engines also have actuator solenoids that can throw similar codes.