Cylinder 12 Misfire Detected
What does P0312 mean?
The P0312 code means the vehicle's onboard diagnostic system has detected: Cylinder 12 Misfire Detected. This is a critical severity code.
Common Symptoms
- Engine misfire on cylinder 12
- Rough idle and vibration
- Check Engine Light flashing
- Reduced power output
- Unburned fuel smell from exhaust
Probable Causes (Ranked by Likelihood)
- Faulty spark plug or ignition coil on cylinder 12 Very High
- Fuel injector failure on cylinder 12 High
- Low compression in cylinder 12 Moderate
- Vacuum leak near cylinder 12 intake Moderate
- Valve train or timing issue on cylinder 12 Low
Step-by-Step Diagnostic Procedure
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Inspect and replace spark plug on cylinder 12 -- check gap and condition
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Swap ignition coil from cylinder 12 with another cylinder and clear codes to retest
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Test fuel injector resistance and pulse signal with a noid light
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Perform a compression test on cylinder 12 -- compare to adjacent cylinders
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Check for vacuum leaks around cylinder 12 intake using a smoke machine
Frequently Asked Questions
Can I drive with code P0312?
You can drive short distances with a steady Check Engine Light. If flashing, pull over immediately to prevent catalytic converter damage.
Is cylinder 12 always the last cylinder?
Yes. On V12 engines, cylinder 12 is the last cylinder, typically located at the rear of one bank. It is often the hardest to access due to its proximity to the firewall.
Can I fix a V12 misfire myself?
If you can access the cylinder, replacing a spark plug or ignition coil is a straightforward DIY task. However, V12 engine bays are very tight, and some cylinders may require significant disassembly to reach.