P02B7
Cylinder 8 - Fuel Trim at Min Limit.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 2
- AreaFuel and air metering (injector circuit)
- B7
- FaultThe specific fault in that area
What it means
P02B7 means the engine control unit has driven the individual fuel trim for cylinder 8 to its minimum limit, so it is removing as much fuel as it is allowed from that cylinder. This normally means the control unit sees that cylinder running richer than expected from the exhaust sensor feedback. Only engines that calculate per-cylinder fuel trims can set this code, and how it is calculated depends on the make and engine.
Symptoms
- Engine management light on
- Rough idle or slight misfire, mainly from cylinder 8
- Smell of fuel or black smoke from the exhaust
- Higher than normal fuel consumption
- Hesitation or uneven running under load
- Possible fuel smell in the engine oil
Possible causes
- Leaking or sticking-open fuel injector on cylinder 8 over-delivering fuellikely
- Injector wiring, connector or driver fault causing incorrect injector operation on cylinder 8possible
- Fuel pressure too high or a fuel pressure regulation fault (a cause that is engine-dependent and usually affects other cylinders too)possible
- Faulty, contaminated or slow exhaust oxygen or air-fuel ratio sensor on the bank containing cylinder 8, giving a false rich readingpossible
- Restricted airflow to cylinder 8, such as heavy intake valve or port carbon build-up, giving a relatively rich mixturepossible
- Mechanical fault on cylinder 8 such as a valve or compression problem upsetting combustion and the exhaust readingrare
How to diagnose
- Read all stored and pending codes and the freeze frame data, noting load, temperature and engine speed when the code set. Look for related misfire, injector or fuel trim codes.
- Inspect the cylinder 8 injector connector, wiring and earths for damage, corrosion, fluid ingress or poor pin tension.
- Check live data for cylinder-specific and bank fuel trims, short and long term, to see whether the problem is isolated to cylinder 8 or wider.
- Check fuel pressure against the manufacturer's specification at idle and under load, and look for a fuel smell in the oil.
- Test the cylinder 8 injector electrically (resistance and drive waveform) and compare it with the other injectors. Use an injector balance or leak-down test where the procedure allows.
- Check the exhaust sensor data for the relevant bank, comparing its response and readings with a known good bank.
- Inspect the intake port and valves of cylinder 8 with a borescope for carbon build-up or oil fouling.
- If the cylinder still looks suspect, carry out a compression or leak-down test following the manufacturer's procedure.
How to fix
- Replace or professionally clean and flow-test a leaking or sticking cylinder 8 injector, as the manufacturer's procedure allows.
- Repair or replace damaged injector wiring, connectors or terminals.
- Correct fuel pressure faults by repairing or replacing the faulty regulator, pump or related component, as diagnosis shows.
- Replace a faulty exhaust sensor once testing proves it is giving false readings.
- Clean carbon deposits from the intake ports and valves of cylinder 8 if they restrict airflow.
- Repair any mechanical engine fault found on cylinder 8, then clear the code and road test to confirm fuel trims return to normal.
Can I keep driving?
The car can usually be driven short distances to a workshop, but book it in soon. A rich or leaking injector can wash oil from the bore, dilute the engine oil and damage the catalytic converter, so avoid hard driving, and stop if it runs very roughly or the engine light flashes.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.