P0312 critical

Cylinder 12 Misfire Detected

The P0312 code means the vehicle's onboard diagnostic system has detected: Cylinder 12 Misfire Detected. This is a critical severity code.

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Keep driving?: Short distances only
DIY difficulty: moderate
Estimated cost: $100 - $800 (parts and labor)

Fix Your Misfire

Magnetic Spark Plug Socket Set with Gap Tool

The #1 fix for misfire codes. 15-piece set with 14mm, 16mm, 18mm magnetic sockets, T-handle extension, and spark plug gapper.

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Diagnose It First

ANCEL AD310 OBD-II Scanner

Read and clear misfire codes. Shows which cylinder is misfiring so you know exactly what to replace.

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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

Inspect and replace spark plug on cylinder 12 -- check gap and condition
Swap ignition coil from cylinder 12 with another cylinder and clear codes to retest
Test fuel injector resistance and pulse signal with a noid light
Perform a compression test on cylinder 12 -- compare to adjacent cylinders
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.