P02B4

Cylinder 7 - Injector Restricted

P02B4 is a generic OBD-II powertrain diagnostic trouble code: Cylinder 7 - Injector Restricted. It is logged by the engine control unit when the fuel/inj monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P02B4
Group
Powertrain
System
Fuel/Inj
Severity
Warning (MIL on, possible limp mode)
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What P02B4 means

P02B4 is a generic OBD-II code set when the PCM determines that the fuel injector serving cylinder 7 is restricted — meaning it is not delivering the commanded volume of fuel within the specified pulse-width window. Modern direct and port fuel injection systems rely on precise metering of atomised fuel; the PCM cross-references crankshaft acceleration patterns, oxygen sensor data, and individual cylinder fuel trim to detect a cylinder producing less torque than its neighbours due to insufficient fuelling. On engines equipped with individual cylinder fuel trim (common in GDI and multi-injection diesel platforms), the PCM can pinpoint the under-fuelling to cylinder 7 specifically. This code only appears on engines with seven or more cylinders. A restricted injector creates a lean combustion event in the affected cylinder, raising combustion temperatures and risking pre-detonation damage to the piston and valves over time. Dirty injector deposits from high-sulphur fuel, low-quality fuel additives, or infrequent service intervals are among the most frequent real-world causes.

Common causes

Most-frequently reported root causes when P02B4 is logged.

  • 1
    Carbon or varnish deposits clogging the injector needle and spray tip of cylinder 7, reducing effective flow
  • 2
    Contaminated fuel (water, sediment, or excessive ethanol content) causing deposit build-up or corrosion inside the injector body
  • 3
    Collapsed or kinked fuel supply line restricting fuel reaching cylinder 7's injector specifically
  • 4
    Weak or failing fuel pump reducing rail pressure to a level where the injector cannot deliver full commanded volume
  • 5
    Partially clogged fuel filter causing insufficient fuel volume under high-demand conditions
  • 6
    Electrical fault causing shortened injector pulse width — wiring damage, chafed insulation, or corroded connector reducing actual open time
  • 7
    Internal injector mechanical failure — worn needle seat or damaged armature coil reducing solenoid travel and flow rate
  • 8
    PCM calibration error or fault causing incorrect injector pulse-width commands to cylinder 7

Symptoms drivers notice

MIL illuminated with P02B4 stored; may accompany a cylinder 7 misfire code (P0307)
Rough idle or hesitation under acceleration as cylinder 7 contributes less torque than commanded
Loss of engine power proportional to the severity of the restriction, more pronounced under high load
Decreased fuel economy as the PCM attempts to compensate by increasing trim on adjacent cylinders
Possible lean exhaust codes (P0171 or P0174) if the restriction is severe enough to shift overall bank trim
Engine may exhibit a slight rhythmic roughness at the firing interval corresponding to cylinder 7

How to diagnose P02B4

A typical diagnostic flow when this code is present.

  1. 1
    Connect a scan tool and check for companion codes; resolve MAF, MAP, or fuel pressure codes first as they can mask or mimic a restricted injector
  2. 2
    Perform a fuel pressure test at idle, at cranking, and under load — compare readings against OEM specification to confirm adequate fuel supply before blaming the injector
  3. 3
    Use the scan tool to perform an injector cut-out or balance test: disabling cylinder 7's injector should produce a smaller RPM drop than cutting healthy cylinders, confirming restricted delivery
  4. 4
    Inspect the fuel injector connector and wiring harness at cylinder 7 for corrosion, chafing, or damaged insulation; measure resistance and coil ohms with a DVOM
  5. 5
    Attempt professional ultrasonic cleaning of the cylinder 7 injector and re-test flow rate on a bench tester — accept if within 5% of specification; replace if outside tolerance
  6. 6
    If cleaning does not restore proper flow, replace the cylinder 7 fuel injector with an OEM-equivalent unit and verify with a follow-up injector balance test
  7. 7
    Clear codes, perform a complete drive cycle, and confirm P02B4 does not return before returning the vehicle to service

Related powertrain codes

Frequently asked questions

Can injector cleaner additives fix a P02B4?

Mild varnish deposits may respond to high-quality fuel system cleaners added to the tank or administered directly through the fuel rail. However, if the injector spray tip is heavily coked or the needle seat is mechanically worn, chemical cleaning will not restore adequate flow. Professional ultrasonic cleaning or injector replacement is needed.

Is P02B4 more common on GDI (gasoline direct injection) engines?

Yes. GDI injectors spray directly into the combustion chamber and are exposed to significantly higher heat and carbon soot compared to port injection. They are more prone to deposit build-up on the injector tip, which restricts the spray pattern and reduces effective flow rate. Regular use of top-tier gasoline and periodic induction cleaning is recommended.

Could a P02B4 be caused by low fuel pressure rather than the injector itself?

Yes. If fuel rail pressure is below specification, every injector in the system effectively delivers less fuel per pulse. In this scenario all cylinders would show lean trim, but the PCM may isolate the leanest cylinder as P02B4. Always test fuel pressure before condemning the injector.

What engines are affected by P02B4?

Only engines with seven or more cylinders can physically generate a cylinder 7 fault. Common applications include V8 petrol and diesel engines (e.g., Range Rover, F-150 5.0L, Dodge RAM 5.7L HEMI, BMW 4.4L N63), V10, and V12 platforms. Inline-8 diesel trucks may also generate this code.

Disabling P02B4 in software

RaceTune can permanently disable P02B4 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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