Possible causes

– Faulty spark plug 12
– Clogged or faulty fuel injector 12
– Faulty ignition coil 12
– Fuel injector 12 harness is open or shorted
– Fuel injector 12 circuit poor electrical connection
– Ignition coil 12 harness is open or shorted
– Ignition coil 12 circuit poor electrical connection
– Insufficient cylinder 12 compression
– Incorrect fuel pressure
– Intake air leak

Tech notes

The P0312 code means that the cylinder 12 is misfiring or is randomly misfiring. Start by checking for intake leaks an if no leaks are found the next step is to replace the spark plugs on cylinder 12. If the problem persist more tests needs to be done to diagnose problem, see “Possible Causes”

When is the code detected?

Engine Cylinder 12 is Misfiring.

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)
– Lack/loss of power
– Hard start
– Engine hesitation

P0312 VOLKSWAGEN Description

When a misfire occurs, engine speed will fluctuate. If the engine speed fluctuates enough to cause the Crankshaft Position (CKP) sensor signal to vary, the Engine Control Module (ECM) can determine that a misfire is occurring.