Fuel and air

P02BB — Cylinder 9 Fuel Trim at Minimum Limit (Mixture Too Rich)

Severity: medium Drive with care, to a shop

What P02BB means

Engines with individual cylinder fuel trim (typically V8 and larger) adjust injection time for each cylinder using oxygen and air-fuel sensor data. P02BB means the ECM has already cut fuel to cylinder 9 as far as it is allowed, yet the mixture still reads rich. The cause is usually excess fuel delivery or misleading sensor readings.

Symptoms

  • Check Engine light on
  • Rough idle
  • Higher fuel consumption
  • Fuel smell or dark exhaust smoke
  • Sluggish acceleration or hesitation
  • Possible misfire on cylinder 9
  • Increased emissions

Possible causes

  1. Leaking or stuck-open fuel injector on cylinder 9
  2. Fuel pressure too high (regulator or return line fault)
  3. Faulty oxygen or air-fuel ratio sensor
  4. Incorrect MAF or MAP sensor readings
  5. Injector wiring or connector fault
  6. Mechanical problem in cylinder 9, such as valve issues
  7. Dirty intake path or corrupted fuel trim adaptation

How to diagnose

  1. Read all codes and freeze frame data, and note any other mixture or misfire codes.
  2. Compare short and long term fuel trim values for cylinder 9 against the other cylinders.
  3. Inspect the cylinder 9 injector connector and wiring for corrosion, chafing or poor contact.
  4. Test fuel pressure and check that it holds after shutdown.
  5. Measure injector resistance and driver signal, using a scope if needed.
  6. Compare oxygen, MAF and MAP sensor readings to expected values.
  7. Check compression and the spark plug on cylinder 9.
  8. After repair, reset adaptations and road test while watching fuel trims.

Common fixes

  • Clean or replace the cylinder 9 injector
  • Replace the fuel pressure regulator or fix the cause of high pressure
  • Replace a faulty oxygen, MAF or MAP sensor
  • Repair the injector wiring or connector
  • Correct the mechanical fault in the cylinder

Questions and answers

What does P02BB mean?

The ECM has reduced fuel to cylinder 9 to its minimum limit and the mixture is still too rich. The cause is excess fuel in that cylinder or sensor data that is misleading the ECM.

Can I drive with P02BB?

Short, gentle trips are usually fine, but don't put off diagnosis. A rich mixture wastes fuel, can dilute the oil and can stress the catalytic converter.

How much does it cost to fix?

It depends on the cause, from cleaning an injector to replacing a sensor or pressure regulator. Diagnosis is needed to know for sure.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.