What are the common causes of P03B9?

Carbon buildup raising compression in cylinder 4. Cylinder 4 injector overfueling. Faulty cylinder 4 pressure sensor reading high. Preignition or knock in cylinder 4. Excess oil in cylinder 4 from worn rings or guides.

Read cylinder 4 pressure live data and check plausibility. Run a compression test on cylinder 4. Check the cylinder 4 injector for overfueling. Inspect the cylinder 4 sensor wiring and connector. Replace the cylinder 4 pressure sensor if compression is normal. Clear the code and retest.

P03B9

Cylinder 4 Pressure Too High

System: Ignition and misfire (P code)
Lamp: Check Engine Light
Category: Powertrain - Ignition

What it means

P03B9 means Cylinder 4 Pressure Too High.

Check these first

Carbon buildup raising compression in cylinder 4
Cylinder 4 injector overfueling
Faulty cylinder 4 pressure sensor reading high
Preignition or knock in cylinder 4
Excess oil in cylinder 4 from worn rings or guides

What to do next

Read cylinder 4 pressure live data and check plausibility
Run a compression test on cylinder 4
Check the cylinder 4 injector for overfueling
Inspect the cylinder 4 sensor wiring and connector
Replace the cylinder 4 pressure sensor if compression is normal
Clear the code and retest

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Updated

Generic SAE J2012 definition. Last updated 2026-10-10.