Fuel and air

P02B7 — Cylinder 8 Fuel Trim at Minimum Limit

Severity: medium Drive with care, to a shop

What P02B7 means

The engine control unit adjusts fuel delivery for each cylinder based on oxygen sensor feedback. P02B7 sets when the correction for cylinder 8 reaches its lower limit: the ECU has removed as much fuel as it is allowed to, yet the mixture still reads too rich. The most common culprit is excess fuel in that one cylinder, such as a leaking injector.

Symptoms

  • Check Engine light on
  • Rough idle or vibration
  • Hesitation and weak acceleration
  • Higher fuel consumption
  • Occasional misfire
  • Fuel smell or dark exhaust smoke

Possible causes

  1. Leaking or stuck-open fuel injector on cylinder 8
  2. Injector wiring or connector fault
  3. Fuel pressure too high (faulty regulator)
  4. Faulty oxygen or mass airflow (MAF) sensor giving wrong readings
  5. Clogged air filter or other cause of a rich mixture
  6. Mechanical problem in cylinder 8, such as worn rings or low compression

How to diagnose

  1. Scan for all codes and freeze frame data, noting any misfire or other fuel trim codes
  2. Compare short and long term fuel trims by bank, and per cylinder if the scan tool supports it
  3. Inspect the cylinder 8 injector connector and wiring; check power and control signal
  4. Measure injector resistance and compare it with neighboring injectors; listen for normal clicking
  5. Test fuel pressure and check the regulator
  6. Check MAF and O2 sensor readings and inspect the air filter
  7. Pull the cylinder 8 spark plug and look for fuel fouling or a gas smell
  8. If needed, run a compression test and an injector leak-down test

Common fixes

  • Replace or professionally clean the cylinder 8 injector
  • Repair the injector wiring or connector
  • Replace the fuel pressure regulator if pressure is too high
  • Replace a faulty MAF or oxygen sensor
  • Replace the air filter and spark plugs, then clear codes and recheck fuel trims

Questions and answers

What does P02B7 mean?

The ECU has reduced fuel to cylinder 8 as far as its correction range allows, but the mixture is still rich. It usually points to that cylinder's injector or to bad sensor data.

Can I just clear P02B7?

You can, but it will return if the cause remains. Check the injector, fuel pressure and sensors first.

Can P02B7 damage the catalytic converter?

Yes. Prolonged rich running sends unburned fuel into the exhaust, which can overheat and damage the catalytic converter, so repair it soon.

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.