P0312 Mercedes-Benz Code - Cylinder 12 Misfire Detected
Quick Answer
Misfire is defined as a lack of combustion in a cylinder due to the absence of a spark, incorrect fuel metering, low compression, or any other cause. Common causes include Faulty Spark Plug #12, Clogged or faulty Fuel Injector #12, Faulty Ignition Coil #12. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
- What it means
- P0312 Mercedes-Benz indicates Cylinder 12 Misfire Detected.
- Common causes
- Common causes include Faulty Spark Plug #12, Clogged or faulty Fuel Injector #12, Faulty Ignition Coil #12.
- Severity
- High - diagnose this code as soon as possible.
- Can I drive?
- Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
Code P0312 Mercedes-Benz Description
When a misfire occurs, engine speed will fluctuate. If the engine speed fluctuates enough to cause the Crankshaft Position (CKP) sensor signal to vary, the Engine Control Module (ECM) can determine that a misfire is occurring.
The Malfunction Indicator Lamp (MIL) blinks once per second when detecting a misfire severe enough to cause catalyst damage. If the MIL is in a steady state due to a misfire, this indicates the threshold for emissions was exceeded and caused the vehicle to fail an inspection and maintenance tailpipe test.
This Diagnostic Trouble Code (DTC) sets when the misfire detection monitor detects an engine misfire in cylinder 12.
What are the Possible Causes of the DTC P0312 Mercedes-Benz?
- Faulty Spark Plug #12
- Clogged or faulty Fuel Injector #12
- Faulty Ignition Coil #12
- Fuel Injector #12 harness is open or shorted
- Fuel Injector #12 circuit poor electrical connection
- Ignition Coil #12 harness is open or shorted
- Ignition Coil #12 circuit poor electrical connection
- Insufficient cylinder 12 compression
- Incorrect fuel pressure
- Intake air leak
How to Fix the DTC P0312 Mercedes-Benz?
Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.
Code Tech Notes
What is the Cost to Diagnose the Code?
Labor: 1.0
To diagnose the P0312 Mercedes-Benz code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.
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Frequently Asked Questions about P0312 Mercedes-Benz Code
1. What are the common symptoms of OBDII code P0312 in a Mercedes-Benz indicating Cylinder 12 misfire?
- Common symptoms include engine misfiring, rough idling, loss of power, and potentially increased fuel consumption.
2. What are the possible causes of OBDII code P0312 in a Mercedes-Benz related to Cylinder 12 misfire?
- Possible causes include faulty spark plugs, ignition coils, fuel injectors, vacuum leaks, low compression, or issues with the engine control module.
3. How can I diagnose the cause of OBDII code P0312 in a Mercedes-Benz for Cylinder 12 misfire?
- Diagnose by checking spark plugs, ignition coils, fuel injectors, performing a compression test, inspecting vacuum lines, and scanning the engine control module for additional error codes.
4. What are some repair tips for resolving OBDII code P0312 in a Mercedes-Benz for Cylinder 12 misfire?
- Repair tips include replacing faulty spark plugs, ignition coils, or fuel injectors, fixing vacuum leaks, performing a carbon cleaning, and ensuring proper engine compression.
5. Can driving with OBDII code P0312 in a Mercedes-Benz for Cylinder 12 misfire cause further damage?
- Continued driving with a misfiring cylinder can potentially damage the catalytic converter, oxygen sensors, and other engine components over time.
6. How important is it to address OBDII code P0312 in a Mercedes-Benz for Cylinder 12 misfire promptly?
- It is crucial to address the issue promptly to prevent further damage to the engine, ensure optimal performance, and maintain fuel efficiency.
7. Is it possible to clear OBDII code P0312 in a Mercedes-Benz for Cylinder 12 misfire without addressing the underlying issue?
- Clearing the code without fixing the root cause will only temporarily remove the warning light, as the issue will likely resurface and potentially worsen over time.
8. Can a DIY enthusiast address OBDII code P0312 in a Mercedes-Benz for Cylinder 12 misfire, or is professional assistance recommended?
- While some simple tasks like replacing spark plugs may be DIY-friendly, diagnosing and repairing more complex issues may require professional assistance to ensure proper resolution.
9. Are there any preventive measures to reduce the likelihood of encountering OBDII code P0312 in a Mercedes-Benz for Cylinder 12 misfire in the future?
- Regular maintenance, such as timely spark plug replacements, using high-quality fuel, and avoiding prolonged idling, can help prevent Cylinder 12 misfire issues.
10. How long does it typically take to repair OBDII code P0312 in a Mercedes-Benz for Cylinder 12 misfire?
- The repair time can vary depending on the specific cause of the misfire, ranging from a quick fix like replacing spark plugs in a few hours to more extensive repairs that may take a day or longer.
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