1. What is P0349 in Mercedes C300 L?

The P0349 OBD-II code stands for Camshaft Position Sensor B Circuit Intermittent. For the Mercedes-Benz C-Class W206 C300 L (2022-2024)—a top-selling European luxury sedan with high market demand—it targets the exhaust camshaft position sensor (Bank 1, Sensor 2) in its M254 2.0T mild-hybrid engine, standard in Luxury, AMG Line, and Exclusive trims (paired with 9-speed 9G-TRONIC transmission).

The M254 engine uses dual camshaft position sensors (intake: G40; exhaust: G163) to sync valve timing with crankshaft rotation. Sensor B refers to the exhaust-side unit, which sends a 0.3–1.0V AC signal to the ECU. P0349 triggers when the ECU detects intermittent signal drops or irregularities (not a constant failure) — often caused by loose connections, sensor wear, or wiring damage.

Mercedes C300 L Specific Note: This code is widespread in 2022-2023 C300 L AMG Line models, per Mercedes Technical Service Bulletin (TSB) 23-02-08. The M254’s exhaust camshaft sensor (#A0009059803) uses a magnetic Hall-effect design that’s sensitive to oil contamination—leaks from the valve cover gasket can seep into the sensor, causing intermittent signal loss that triggers P0349.

2. Common Causes of P0349 in 2022-2024 C300 L

P0349 in Mercedes C300 L M254 models stems from intermittent camshaft sensor signal issues—below are real-world cases diagnosed with the ICARZONE UR800:

• Sensor Oil Contamination (2023 C300 L AMG Line): An owner with 38,000 miles reported random engine misfires. The UR800’s Camshaft Sensor Signal Test showed intermittent signal drops (0V for 0.5–1s). Replacing the oil-soaked sensor (#A0009059803) and valve cover gasket (#A0000104280) per TSB 23-02-08 fixed P0349.
• Loose Wiring Connector (2022 C300 L Luxury): A Luxury trim owner’s P0349 reappeared after rough road driving. The UR800’s Circuit Continuity Test detected intermittent resistance spikes (10–15Ω). Securing the sensor connector with dielectric grease resolved the signal loss.
• Sensor Internal Wear (2024 C300 L Exclusive): A 2024 C300 L owner’s P0349 triggered during highway acceleration. The UR800’s Sensor Response Test showed inconsistent signal frequency. Replacing the worn sensor with OEM #A0009059803 stabilized readings.
• ECU Software Glitch (2022 C300 L AMG Line): An AMG Line owner’s P0349 occurred after a firmware update. The UR800’s ECU Version Check showed outdated software (v1.5.0). Updating to v2.1.0 via UR800 fixed signal processing errors.

3. Key Symptoms of P0349 in M254 Engine

P0349 symptoms in the Mercedes C300 L are intermittent (matching the fault code’s nature)—watch for these signs that signal erratic camshaft sensor signals:

4. C-Class Trims/Engines Prone to P0349

Mercedes service data highlights these 2022-2024 C-Class configurations with the highest P0349 occurrence rates (all M254 engines):

5. Diagnose P0349 with ICARZONE UR800

Diagnose P0349 in your Mercedes C300 L M254 accurately with the UR800’s Mercedes-specific camshaft sensor tools. Follow these steps (engine at operating temperature; battery voltage 12.4–12.7V):

Case Example: A 2023 C300 L AMG Line failed Step 2 (0V spikes) and Step 5 (TSB 23-02-08 eligible). The UR800’s Component Location Tool guided sensor access (passenger-side cylinder head, near the exhaust manifold). Inspection revealed oil-soaked sensor—replacing it and the valve cover gasket eliminated signal drops, clearing P0349.

6. How to Fix P0349 in Mercedes C300 L

Resolve P0349 in your C300 L with these UR800-verified solutions—tailored to the M254 engine’s camshaft sensor system:

1. Replace Exhaust Camshaft Sensor + Valve Cover Gasket (Most Common Fix for TSB 23-02-08)

1. Confirm oil contamination via UR800’s Step 2. Disconnect the negative battery terminal and remove the engine cover (4 Torx T30 screws).
2. Locate the exhaust camshaft sensor (G163): Passenger-side cylinder head, near the exhaust manifold, with a 3-pin electrical connector.
3. Disconnect the connector (press the release tab) and remove the sensor (1 Torx T25 screw). Inspect for oil residue—confirm contamination.
4. Remove the valve cover (10 Torx T30 screws) and old gasket. Clean the cover mating surface with solvent to remove oil buildup.
5. Install OEM parts:
   • Exhaust camshaft sensor: #A0009059803
   • Valve cover gasket: #A0000104280
   Torque the valve cover to 8 ft-lbs (crisscross pattern) and sensor to 6 ft-lbs.
6. Reconnect the sensor connector and battery. Use UR800 to retest signal stability (no 0V spikes). Clear P0349 and test drive—confirm no misfires.

2. Secure Loose Connector (for Intermittent Resistance Spikes)

1. Confirm loose connector via UR800’s Step 3. Disconnect the sensor connector and inspect pins for corrosion or bent contacts.
2. Clean pins with electrical contact cleaner (#CRC 05103) and straighten any bent pins with a small screwdriver.
3. Apply a thin layer of dielectric grease (#Permatex 81150) to the connector pins—prevents moisture and secures contact.
4. Reconnect the connector until it clicks into place. Use a zip tie to secure the wiring harness to the engine bay bracket—reduces vibration.
5. Use UR800 to retest continuity (stable <1Ω). Clear P0349 and test drive on rough roads—verify no signal spikes.

3. Update ECU Software (for Firmware Gaps)

1. Confirm outdated software via UR800’s Step 4. Connect UR800 to the OBD-II port (under the steering wheel) and turn the key to "ON."
2. Select "ECU" > "Software Update" > "Download Latest Version." The UR800 will detect the current firmware and install the latest (v2.1.0 for 2022+ C300 L).
3. Do not turn off the key or disconnect UR800 during the update (takes 15–20 minutes). The tool will alert you when the ECU reboots.
4. Use UR800 to retest camshaft sensor signal processing—confirm no irregularities.
5. Clear P0349 with UR800 and test acceleration—ensure smooth power delivery with no hesitation.

7. P0349 Repair Costs & Maintenance Tips

P0349 repair costs for the Mercedes C300 L M254 vary by cause. Use this table to budget:

Maintenance Tips for C300 L Owners

• C300 L AMG Line (2022-2023): Inspect the exhaust camshaft sensor and valve cover gasket every 30,000 miles—replace per TSB 23-02-08 to avoid oil contamination and P0349.
• Luxury trim owners (frequent rough road driving): Secure the sensor wiring harness with zip ties every 15,000 miles—prevents loose connections that cause intermittent signals.
• Update ECU software via UR800 every 12 months—fixes signal processing bugs that trigger false P0349 codes in 2022+ C300 L models.
• Use Mercedes-approved engine oil (5W-40 synthetic) and replace every 7,500 miles—reduces valve cover gasket leaks that contaminate the sensor.
• Perform the UR800’s Camshaft Sensor Health Check every 10,000 miles — monitor signal stability and connector resistance to catch issues before P0349 triggers.

8. C300 L-Specific FAQs