Fuel and air

P02A7 — Cylinder 4 Fuel Trim at Minimum Limit

Severity: medium Drive with care, to a shop

What P02A7 means

P02A7 means the engine control unit is pulling as much fuel as it is allowed to from cylinder 4 and has hit the minimum trim limit. This usually points to a mixture that is too rich in that cylinder, which the ECU can no longer correct. Normally the system keeps the mixture near ideal by constantly adjusting injector pulse width based on oxygen sensor feedback.

Symptoms

  • Check Engine light on
  • Rough idle or stumbling at low speed
  • Misfire on cylinder 4
  • Reduced power and sluggish acceleration
  • Poor fuel economy
  • Fuel smell, black smoke or sooty spark plug

Possible causes

  1. Leaking or stuck-open fuel injector on cylinder 4
  2. High fuel pressure from a faulty pressure regulator
  3. Electrical fault in the injector, its wiring or connector
  4. Faulty or slow oxygen or air-fuel ratio sensor
  5. Dirty or faulty mass airflow sensor
  6. Mechanical or ignition problem in cylinder 4 (low compression, weak spark)
  7. ECU software or internal fault (rare)

How to diagnose

  1. Scan for codes and freeze frame data, and note any other mixture or misfire codes
  2. Watch short-term and long-term fuel trims in live data; strongly negative values confirm a rich condition
  3. Inspect the cylinder 4 injector connector and wiring for corrosion, damage or poor grounds
  4. Measure injector resistance and check the drive signal with a scope or noid light
  5. Test fuel pressure and how well it holds after shutoff
  6. Pull the cylinder 4 spark plug; black soot suggests over-fueling
  7. Run an injector balance test, or swap injectors with a neighbor cylinder and see if the problem follows
  8. Check mass airflow and oxygen sensor readings for plausibility

Common fixes

  • Clean or replace the cylinder 4 fuel injector
  • Replace the fuel pressure regulator or fix the cause of high pressure
  • Repair the injector wiring or connector
  • Replace a faulty oxygen or mass airflow sensor
  • Replace the spark plug or coil on cylinder 4 if misfiring
  • Update the ECU software if the manufacturer recommends it

Questions and answers

What does P02A7 mean?

The ECU has reduced fuel to cylinder 4 as far as it can because the mixture is running too rich. The injector on that cylinder is the most common culprit.

Can I drive with P02A7?

Short trips are usually fine, but don't put it off. Excess fuel can foul plugs, dilute oil and damage the catalytic converter.

How can I tell a bad injector from a wiring problem?

Swap the injector with another cylinder and see if the fault follows it, and measure its resistance and check the connector. If the code stays on cylinder 4, look at the wiring or a mechanical issue.

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.