Fuel and air

P0266 — Cylinder 2 Contribution/Balance Fault

Severity: medium Drive with care, to a shop

What P0266 means

The engine control module constantly compares how much each cylinder contributes to engine output, for example through crankshaft speed changes. P0266 means cylinder 2 is noticeably weaker than the rest. The most common cause is the cylinder 2 fuel injector or its circuit, but other systems can be responsible too.

Symptoms

  • Check engine light on
  • Rough or shaky idle
  • Reduced power and sluggish acceleration
  • Higher fuel consumption
  • Misfire-like stumbling or hesitation
  • Raw fuel smell from the exhaust

Possible causes

  1. Clogged or failing fuel injector on cylinder 2
  2. Damaged injector wiring or a poor connector contact
  3. Low fuel pressure (weak pump, clogged filter)
  4. Worn spark plug or failing ignition coil on cylinder 2
  5. Vacuum leak near the cylinder 2 intake port
  6. Low compression in cylinder 2 (rings, valves, head gasket)
  7. Rarely, an ECM fault or software problem

How to diagnose

  1. Scan all codes and freeze frame data, and look for misfire codes such as P0302
  2. Inspect the cylinder 2 injector connector and wiring for damage, corrosion or loose pins
  3. Swap the cylinder 2 coil and spark plug with a neighbor and see if the fault follows
  4. Listen to the injector with a stethoscope and measure its resistance
  5. Check fuel pressure at the rail and the condition of the fuel filter
  6. Look for intake vacuum leaks, hoses and manifold gasket problems
  7. Run a compression or leak-down test on cylinder 2
  8. Check the injector drive signal with a scope or noid light

Common fixes

  • Clean or replace the cylinder 2 fuel injector
  • Repair the wiring or replace the damaged connector
  • Replace the spark plug or ignition coil on cylinder 2
  • Replace the fuel filter or pump if pressure is low
  • Fix any vacuum leak
  • Repair the engine if compression is low
  • Reflash or replace the ECM only after the fault is confirmed

Questions and answers

What does P0266 mean?

It means the ECM sees cylinder 2 contributing less power than the other cylinders. The injector or its circuit is the usual suspect, but spark, air leaks and mechanical wear must be ruled out.

Can I drive with P0266?

Only briefly and under light load. Running for long with a weak cylinder can damage the catalytic converter and make the underlying problem worse.

How can I quickly test the cylinder 2 injector?

Check the connector and wiring, listen for the injector clicking, and measure its resistance. Then compare it with a neighboring injector or swap them to see if the fault moves.

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.