P0312 OBD-II Trouble Code: Cylinder 12 Misfire Detected

Our certified mechanics come to you · Get a fair and transparent estimate upfront

Red-stars EXCELLENT RATING ON

Cost of diagnosing the P0312 code

P0312 is a diagnostic trouble code (DTC) for "Cylinder 12 Misfire Detected". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.

Cars Estimate Credit towards follow-up repair Earliest Availability
Ford$20.00
Toyota$20.00
BMW$20.00
SCHEDULE P0312 DIAGNOSTIC Get a fair and transparent estimate upfront

P0312 code definition

The definition of trouble code P0312 is that cylinder #12 has misfired.

What the P0312 code means

Every vehicle’s engine relies on the use of cylinders to operate. Each of these cylinders needs a spark plug that is located at its top. These spark plugs fire one after the next to ignite the mixture of air and fuel that is necessary for a vehicle’s engine to work.

Once ignited, the mixture produces energy that then pushes the crankshaft. Cylinders take turns to regulate the crankshaft’s rotation. Firing in sequence like this allows the crankshaft to rotate seamlessly and the vehicle to traverse the road smoothly.

Sometimes, a cylinder will misfire. When this happens, the RPM (revolutions per minute) of the crankshaft may increase or decrease. There is a predetermined range of RPM the manufacturer has deemed as appropriate for the vehicle. If a misfire causes the crankshaft to reach an RPM that is 2% above or below this range, the PCM (powertrain control module) will store a trouble code. In a 12-cylinder engine, when the cylinder responsible for the misfire is #12, the code that is logged is P0312.

What causes the P0312 code?

The easiest diagnosis and by far the most common reason for P0312 to be stored is that something is wrong with its spark plug. It could be completely broken or it might have become dirty somehow.

There could also be a lack of compression in this cylinder. That would lead to a lack of RPMs because there wouldn’t be as much power coming out.

Other common causes are:

  • Burned valves
  • Faulty fuel injectors
  • Bad ignition timing
  • A vacuum leak
  • Faulty crankshaft sensor
  • Faulty camshaft sensor
  • Faulty mass airflow (MAF) sensor
  • Problems with the catalytic converter

Although it’s hardly ever the case, it is possible that the PCM is malfunctioning. If that were the case, though, you most likely wouldn’t experience the following symptoms.

What are the symptoms of the P0312 code?

As with a lot of trouble codes, P0312 will cause the Check Engine Light to come on. If the RPMs go above or below the margin by up to 10%, the light is activated. However, one big difference is that with this code, the light can actually be made to blink. This is what happens if RPMs go outside 10% of the acceptable margin. That’s because it means the #12 cylinder is misfiring because it isn’t getting a spark from its spark plug – a much more serious problem.

Other symptoms include:

How does a mechanic diagnose the P0312 code?

A mechanic will begin by using an OBD-II scanner to find out which problem codes have been stored by the PCM. They will then inspect the engine components. This would include cylinder #12, its spark plug, wiring and connectors. After making necessary repairs and replacements, a test drive would be necessary while the scanner is plugged in and live.

Common mistakes when diagnosing the P0312 code

The most common mistake is when a mechanic just replaces the spark plug and assumes that will be sufficient. As you can probably tell from the above, a P0312 code can represent a number of other problems too so even if the spark plug was faulty a comprehensive diagnosis must still be carried out.

How serious is the P0312 code?

This is definitely a code to take seriously. Some of the potential symptoms we mentioned above could actually make it dangerous to operate the vehicle. Even if the dangerous symptoms aren’t present, it will still be difficult to drive an automobile with this code.

What repairs can fix the P0312 code?

The following repairs are usually sufficient:

The worst case scenario would be having to replace the engine because cylinder damage had become so extensive.

Additional comments for consideration regarding the P0312 code

Always replace spark plugs in pairs. However, P0312 usually means that the rest of the vehicle could do with a tune-up too, so it’s probably best to have one carried out in the near future.

Need help with a P0312 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

trouble codes
Check Engine Light
P0312

No more waiting rooms! Our mechanics will come to you to diagnose and fix the P0312 code.

SCHEDULE P0312 DIAGNOSTIC
Get a $20 credit for the follow-up repair

Recent Check Engine Light is on Inspection reviews

Excellent Rating

(6,144)

Rating Summary
5,685
221
51
35
152
5,685
221
51
35
152

Chris

11 years of experience
13 reviews
Chris
11 years of experience
Ford F-150 - Check Engine Light is on - North Salt Lake, Utah
We were having problems with our check engine light, and Chris was exceptionally thorough until he found the problem and could help resolve the situation. We appreciate having someone who cares enough to get the job done right, not just done. We will definitely use Chris' services in the future. Thanks Chris.

Leng

21 years of experience
2 reviews
Leng
21 years of experience
Mazda MPV - Check Engine Light is on - Seattle, Washington
Leng arrived on time and explained the issue that my van is having. I will make a follow up appointment for the fix. Friendly, easy to talk to, and professional - thank you very much!

Okela

13 years of experience
11 reviews
Okela
13 years of experience
Land Rover LR4 - Check Engine Light is on - Brooklyn, New York
Okela was incredible! He is super thorough and took time to walk us through the issues with our LR4. Couldn’t recommend more! Thank you Okela!!

Robert

37 years of experience
188 reviews
Robert
37 years of experience
Land Rover LR2 - Check Engine Light is on - Atlanta, Georgia
Robert arrived on time. Did a diagnostic check quickly. He was friendly, and gave great service. He knows how to work on a Land Rover.


More related articles

P0121 OBD-II Trouble Code: TPS "A" Circuit Range Performance Problem
P0121 code definition Throttle Pedal Position Sensor/Switch (TPS) A Circuit Range Performance Problem What the P0121 code means P0121 is a generic...
P2238 OBD-II Trouble Code: O2 Sensor Positive Current Control Circuit Low Bank 1 Sensor 1
What the P2238 code means? P2238 is an OBD-II generic code for the engine control module (ECM) detecting the O2 sensor for...
P0871 OBD-II Trouble Code: Transmission Fluid Pressure Sensor/Switch C Circuit Range/Performance
P0871 means there is an issue with the transmission fluid pressure, possibly that it is low, the pump is faulty, or the sensor is dirty.

Related questions

Hi Patrick my car has the code p1090 coming out I got the part and wanted to know what else I should look out for in my car and to

You should go ahead and replace the actuator first and then clear the codes and road test to see if the system operates correctly and if the code returns then you may have to have further diagnosis of the electrical...

Check Engine Light appears and disappears, engine misfires occasionally

Many common faults will cause misfires on your 2006 Honda Pilot. Without knowing what check engine light your vehicle has I can only offer general advice on the issue. The most common causes are spark plugs, plug wires, MAF sensor,...

I change my oil change oil filter fuel pump and filter spark plugs and wires distruibor cab and rotor. Truck shakes why?

If your Check Engine Light is coming on, a fault code should be stored in the ECM. A flashing Check Engine Light indicates a potentially serious engine failure. Since the situation you are experiencing can be caused by any number...

How can we help?

Our service team is available 7 days a week, Monday - Friday from 6 AM to 5 PM PST, Saturday - Sunday 7 AM - 4 PM PST.

1 (855) 347-2779 · hi@yourmechanic.com