P0312
Cylinder 12 Misfire DetectedP0312 is a generic OBD-II powertrain diagnostic trouble code: Cylinder 12 Misfire Detected. It is logged by the engine control unit when the misfire monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0312 means
P0312 is an OBD-II powertrain code that the engine control module has detected a misfire on cylinder number 12. Like P0311, this code is physically restricted to engines that possess a twelfth cylinder — in practice exclusively V12 engines used in premium and performance vehicles from BMW, Mercedes-Benz, Audi, Ferrari, Lamborghini, Rolls-Royce, Bentley, and Aston Martin. It cannot appear on any engine configuration with fewer than 12 cylinders.
The ECM continuously measures crankshaft rotational velocity and identifies the power-stroke contribution of each cylinder. When cylinder 12's expected acceleration pulse is absent or insufficient, the PCM logs a misfire event for that cylinder's position. If the misfire rate exceeds a threshold defined per drive cycle (typically 2% of firing events over 200 crankshaft revolutions for catalytic converter damage thresholds), the MIL illuminates — and will flash if the rate is high enough to actively damage the catalyst.
The root causes are identical to those for any individual cylinder misfire: a degraded spark plug, failed coil-on-plug, faulty or clogged fuel injector, low cylinder compression from valve or gasket failure, or a wiring fault in the coil driver circuit. Cylinder 12 on most V12 architectures is the rearmost cylinder on one bank, often the most inaccessible position in the engine bay, making physical inspection and part swapping more labour-intensive than on smaller engines.
Common causes
Most-frequently reported root causes when P0312 is logged.
-
1
Worn or fouled spark plug on cylinder 12 failing to initiate or sustain combustion.
-
2
Failed ignition coil-on-plug unit on cylinder 12 with no or intermittent spark output.
-
3
Clogged, leaking, or electrically dead fuel injector on cylinder 12.
-
4
Low compression on cylinder 12 due to burnt exhaust valve, head gasket failure, or worn piston rings.
-
5
Damaged wiring, broken wire, or corroded connector in the ignition driver circuit for cylinder 12.
-
6
Vacuum or boost leak at the intake manifold port or gasket serving cylinder 12.
-
7
Faulty crankshaft or camshaft position sensor generating erroneous misfire cylinder identification.
Symptoms drivers notice
How to diagnose P0312
A typical diagnostic flow when this code is present.
-
1
Use a professional-grade scan tool to confirm P0312 and retrieve freeze frame data; check for companion misfire codes on adjacent cylinders.
-
2
Monitor live per-cylinder misfire counters to confirm cylinder 12 is the primary fault source.
-
3
Swap the cylinder 12 ignition coil and spark plug with a known-good cylinder and re-run the engine to determine if the misfire migrates — confirming or ruling out the ignition components.
-
4
Test the cylinder 12 fuel injector electrically (resistance, balance rate via scan tool) and with a stethoscope for audible operation; swap if suspect.
-
5
Perform a cylinder compression test and leak-down test on cylinder 12 to identify any mechanical fault.
-
6
Inspect the cylinder 12 coil wiring harness for heat damage, chafing, or corroded pins, which are common on high-mileage V12s.
-
7
Verify ECM coil driver output with an oscilloscope if all external components test serviceable.
Related powertrain codes
Frequently asked questions
Which specific V12 engines are most commonly associated with P0312?
Common examples include the BMW N73/N74 (7 Series/Rolls-Royce), Mercedes-Benz M120/M275/M279 (S/CL/SL 600), Audi/Bentley W12, Ferrari 612/F12, and Lamborghini Murcielago/Aventador V12 platforms. Each has its own firing order and cylinder numbering convention.
Can I drive the vehicle with P0312 active?
Limited low-speed driving to a workshop is generally possible, but sustained driving risks catalytic converter damage (very expensive on V12 vehicles) and potential bore wash from unburned fuel. A flashing MIL is a stop-driving signal.
How is cylinder 12 numbered — is it the same position on all V12s?
No. Cylinder numbering conventions vary by manufacturer. On most V12s the cylinders are numbered 1–6 on one bank and 7–12 on the other, but the starting bank and direction differ. Always verify the OEM-specific cylinder layout diagram before accessing the engine physically.
Would a failing ignition coil on cylinder 12 always produce P0312 alone?
Not necessarily. A partially failing coil may cause intermittent misfires that also set P0300 (random/multiple cylinder misfire) alongside P0312. A completely open coil typically produces a consistent P0312 with a high cylinder-12 misfire count.
Disabling P0312 in software
RaceTune can permanently disable P0312 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
Got P0312 in your scan?
Upload your ECU file — we'll identify the exact software version and confirm whether a disable is available for your car.
Upload your file