OBD-II Code
P0312
Severity
Not yet reviewed
Nobody on our side has assessed this code yet, so we are not going to guess at how serious it is.
Can you drive it
We cannot say
Treat it as unknown until a shop reads it with live data. If the check-engine light is FLASHING, stop driving as soon as it is safe to — that means an active misfire, whatever the code.
Indicative cost (USD)
$180–$4,500
From this code's diagnostic notes. Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
P0312 is cylinder 12 misfire detected — V12 only, and almost always the very last cylinder in the firing order on the right bank, physically tucked against the firewall on FR V12 platforms.
How a shop works this
The ECU has already told you which cylinder. That makes the fastest honest test a swap: move one part to another cylinder and see whether the fault moves with it. It identifies the fault instead of guessing at it, and it costs nothing.
Photograph the coils before you touch anything, and note which is which.
Cylinder numbering is not the same across manufacturers, and V6 and V8 bank layouts differ by maker — look up the firing order and bank layout for your engine before you move parts, or you can spend an hour swapping coils on the wrong bank.
Move the cylinder 12 ignition coil to a cylinder that is not misfiring, put that cylinder's coil on 12, clear the code, and run it until the misfire returns.
On a modern coil-on-plug engine the coil is the most common single answer to a cylinder-specific misfire, which is why it is the first thing to move — not because it is the cheapest part. A misfire that is there even at idle is the classic dead-coil pattern.
- The misfire follows the coil to its new cylinderThe coil is the fault. Replace it. If the engine has real mileage on it, the other coils are on the same clock.
- The misfire stays on cylinder 12The coil is fine. Look at the coil connector and the harness around it next — chafed and rodent-damaged connections at that plug are a common second answer — then pull the plug.
Read the plug you pulled, and check the boot for carbon tracking.
Black and sooty means it has been running rich. White or blistered means lean or too hot. Oil-wet points at valve seals or rings. Fuel-wet points at an injector holding open. A carbon-tracked boot arcs to the head and imitates a dead coil for the price of a new boot. On an older engine with a distributor, the cap, rotor and plug wires belong in this step too.
If spark is accounted for, go to fuelling, then to compression.
An injector balance or flow test comes first because it is quicker. Compression test second: a cylinder more than about 15% below its neighbours is mechanical, and no ignition part will fix it. A vacuum leak on this one runner sits alongside these — a leak big enough to affect every cylinder would be setting P0300 instead.
A flashing check-engine light means the misfire is putting raw fuel into the catalytic converter, which can destroy it quickly. Stop driving as soon as it is safe to. A steady light with a mild misfire is less urgent, but stop anyway if it shakes hard, loses power, overheats, or makes a noise it was not making before.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Check engine light
Likely causes
- Failed ignition coil (cylinder 12)Most common
- Damaged coil connector or harness at cylinder 12
- Worn spark plug or carbon-tracked boot (cylinder 12)
- Clogged or leaking fuel injector (cylinder 12)
- Low compression on cylinder 12
- Vacuum leak at the cylinder 12 intake runner
Read the full diagnostic procedureP0312 is cylinder 12 misfire detected — V12 only, and almost always the very last cylinder in the firing order on the right bank, physically tucked a…
P0312 is cylinder 12 misfire detected — V12 only, and almost always the very last cylinder in the firing order on the right bank, physically tucked against the firewall on FR V12 platforms.
The mechanical diagnostic ladder is identical to P0311
- swap coil, inspect plug, swap injector, compression test, leak-down.
- The labor reality is brutal — on a 760Li the cylinder 12 coil is under the intake plenum at the rear corner, requiring 1.5-2 hours of disassembly to reach a $90 part.
- Before tearing into the engine, verify fuel pressure on the failing bank, and read VANOS/camshaft adaptation values bank-specifically.
- If bank 2 cam timing shows a 4+ degree offset from commanded, the bank-2 VANOS solenoid or cam phaser is the cause and cylinder 12 is just the most-affected cylinder in the firing event.
- Caveat: P0312 with a coolant smell and a slightly low coolant level points to a cracked head or head gasket weeping into cylinder 12 — pressure-test the cooling system before authorizing any mechanical work because a head replacement on a V12 is a 25-hour job.
Vehicle-specific patternsBMW N74 V12 (760Li F02/G12, Rolls-Royce Ghost/Wraith/Phantom VIII, 2009+) — cylinder 12 misfire frequently traces to the right-bank high-pressure fue…
BMW N74 V12 (760Li F02/G12, Rolls-Royce Ghost/Wraith/Phantom VIII, 2009+) — cylinder 12 misfire frequently traces to the right-bank high-pressure fuel pump; the N74 uses two HPFPs (one per bank). Replace pump and prime per ISTA procedure ($1,400-2,200 in parts). BMW N73 V12 (E65 760i, 2003-2008) — bank-2 VANOS solenoid wear causes cylinder 12 cold-start misfire that clears after warm-up. Mercedes M279 V12 biturbo (S65 AMG, S600 W222, 2014+) — cylinder 12 misfire under load is almost always the rear-bank ignition coil failing from heat soak between the turbo and the firewall. Ferrari 612/599/F12 V12 (F133/F140 platforms) — cylinder 12 spark plug fouling from oil ingestion past tired valve stem seals on cars above 50K miles.
Estimated repair$180 to $4,500.
Look up another code
P0312 — frequently asked
What does a P0312 code mean?
See deep dive below for full diagnostic context.
What causes a P0312 code?
Common causes: Failed ignition coil (cylinder 12); Damaged coil connector or harness at cylinder 12; Worn spark plug or carbon-tracked boot (cylinder 12); Clogged or leaking fuel injector (cylinder 12); Low compression on cylinder 12; Vacuum leak at the cylinder 12 intake runner.
What are the symptoms of a P0312 code?
Typical symptoms: Check engine light.
Is it safe to drive with a P0312 code?
Depends on the light. Flashing: stop as soon as it is safe to — raw fuel is reaching the catalytic converter. Steady, and it only feels rough: a short drive to a shop is usually fine. Either way, stop if it shakes hard, loses power, overheats or makes a new noise. Estimated repair: $50-$2,000.
How do I diagnose a P0312 code?
The ECU has already told you which cylinder. That makes the fastest honest test a swap: move one part to another cylinder and see whether the fault moves with it. It identifies the fault instead of guessing at it, and it costs nothing. 1. Photograph the coils before you touch anything, and note which is which. 2. Move the cylinder 12 ignition coil to a cylinder that is not misfiring, put that cylinder's coil on 12, clear the code, and run it until the misfire returns. 3. Read the plug you pulled, and check the boot for carbon tracking. 4. If spark is accounted for, go to fuelling, then to compression.
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