Powertrain, generic · Ignition system or misfire

P03AF Cylinder 3 Pressure Too High

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

Some diesels have a combustion pressure sensor in the glow plug; the engine module uses it to control injection for each cylinder. This code concerns cylinder 3. P03AF means the pressure measured or calculated for the cylinder is higher than expected. It is documented by code at Audi, surprisingly on a petrol engine: on the 2015 S3 (2.0 TFSI, engine CYFB) the four 'pressure too high' codes came on with the EPC lamp, usually together with misfire codes P0300–P0304 and the manufacturer code for hiding a cylinder; the cause was a software fault that mis-detected misfire, and a software update fixed it. How Audi determines the pressure, the bulletin does not say. On diesels with pressure-sensing glow plugs GM patents describe a peak pressure above its limit – too much or too early injection, or a sensor drifting upwards. If the cylinder is shut off, power drops noticeably.

Likely causes

Engine module software (Audi S3 2015, engine CYFB)
Injector delivering too much or dripping
Sensor drifting upwards (diesel pressure-sensing glow plug)
Knock or pre-ignition on a petrol engine

Symptoms

  • EPC or check engine light on
  • Misfire codes, possibly a cylinder shut off with noticeable loss of power
  • Rough running

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–800
Time0.5–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

cylinder pressure sensor glow plugsensor wiringengine control modulefuel injector

Related codes

P03AEP03AAP03B2P0303P039BP03A5

References: static.nhtsa.gov, static.nhtsa.gov, patents.google.com, law.cornell.edu.