P03BB

Code

Generic P — Powertrain

Cylinder 4 Pressure Variation High

Brand: Generic

Type: P — Powertrain

Views: UK: 35 EN: 49 RU: 38

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Page language: EN

Causes

Faulty ignition coil or spark plug on cylinder 4 (weak or no spark)
Fuel injector partial clog, leak, or electrical fault on cylinder 4
Low compression in cylinder 4 (piston rings, cylinder wall, valves, head gasket)
Valve timing error (timing belt/chain jump or cam phasing fault)
Intake or vacuum leak localized to cylinder 4
Cylinder pressure sensor or CMP/CKP timing sensor fault or poor signal

Symptoms

Check Engine Light (MIL) illuminated
Rough idle or vibration, often felt as a misfire
Poor acceleration or loss of power, especially under load
Increased fuel consumption and higher emissions
Intermittent or persistent misfire codes (may coincide with P03BB)
Possible hard starting or stalling in severe cases

What to check

Read freeze frame and live data with a capable scan tool; record misfire counts and related parameters
Confirm code is repeatable: clear codes, run engine and drive to re-create
Inspect spark plug, ignition coil, and wiring for cylinder 4 for damage or carbon tracking
Check injector resistance and operation (pulse) for cylinder 4
Quick cylinder balance or cylinder cutoff test (if available) to isolate cylinder contribution
Perform a basic fuel pressure check at the rail

Signal parameters

Cylinder pressure amplitude or relative pressure variation (engine-specific units)
Cylinder-specific misfire count for cylinder 4
Crank/Cam position sensor signals (phase and timing)
Ignition coil primary/secondary waveform (voltage, dwell)
Injector pulse width and current (ms / A)
Fuel rail pressure (kPa or bar)

Diagnostic algorithm

Capture freeze frame and live data. Note conditions when P03BB set (RPM, load, temperature, fuel trims).
Visually inspect and secure connectors for cylinder 4 coil, injector, and any cylinder pressure or related sensors.
Swap the ignition coil (or coil-on-plug) from cylinder 4 to another known-good cylinder. Re-scan for code. If code follows coil, replace coil.
Swap the spark plug from cylinder 4 with another cylinder. Inspect plug for fouling, deposits, or damage. Replace if suspect.
Swap the injector (or use injector balance test) between cylinder 4 and another cylinder. If the problem follows the injector, service or replace it.
Check fuel rail pressure and supply. Verify injector pulse via scope or noid light and listen for injector operation at cylinder 4.
Perform a static compression test and/or leak-down test on cylinder 4 and compare to other cylinders to identify mechanical issues.
Verify camshaft and crankshaft position timing (timing belt/chain condition and phasing). Check for jumped timing or incorrect cam phaser operation.
Inspect intake manifold gasket and local vacuum lines for leaks around cylinder 4; perform smoke test if necessary.
Use oscilloscope to compare coil and injector waveforms, crank/cam signals, and cylinder pressure waveform (if vehicle has a pressure sensor) to other cylinders.
If wiring or sensor fault suspected, backprobe and measure continuity/resistance; repair damaged harness or connector.
After repairs, clear codes and perform a full drive cycle under the conditions noted in freeze frame to confirm the fault is resolved.

Likely causes

Ignition coil or spark plug failure on cylinder 4
Fuel injector electrical fault or mechanical restriction for cylinder 4
Low mechanical compression (rings, valves, head gasket) in cylinder 4
Cam/crank timing or phasing error affecting valve timing on cylinder 4
Faulty cylinder pressure sensor or related wiring/connector

Fault status

⚠️ Status

Cylinder 4 pressure variation exceeded threshold. ECM set P03BB — possible cylinder 4 misfire, fuel or ignition fault, mechanical compression loss, timing issue, or sensor/wiring fault.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.5-3.0 hours