P026C: Fuel Injection Quantity A Lower Than Expected

What it means

Fuel injection quantity A is lower than the commanded amount. Often clogged or worn injector.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test
• The engine or gearbox may go into limp mode

How it works

The engine control module estimates or monitors fuel injection quantity A and compares it with the amount it commands. This code sets when the measured or inferred quantity is too low, which can result from a restricted injector, inadequate fuel supply, or a fault in injector control.

Common causes

Most likely first.

1. Injector restricted or worn
2. Low fuel pressure
3. Fuel supply restriction
4. Injector wiring or control fault

Symptoms

• Check-engine light
• Rough running or misfire
• Hard starting
• Reduced power

How to diagnose it

1. Review freeze-frame data and live commanded-versus-reported injection quantity A, along with misfire and fuel-pressure data, to identify when delivery falls short.
2. Inspect the injector wiring and connectors for damage, loose pins, or corrosion that could limit its operation.
3. Check the fuel filter, lines, and other supply path for restriction or damage, and compare fuel pressure with the manufacturer's specification.
4. Use the vehicle's specified injector balance or delivery test to check for a restricted or worn injector.
5. If fuel supply and injector condition pass, test the injector control circuit and relevant module data using the wiring diagram.

Common fixes

• Repair a loose or corroded injector connector or damaged control wiring.
• Correct a confirmed restriction in the fuel supply path.
• Replace a restricted or worn injector if delivery testing confirms it.
• Repair a fuel pressure problem after identifying its source.
• Repair the injector control circuit if testing rules out fuel supply and injector faults.

Can I keep driving?

With reduced-power operation possible, avoid overtaking, steep climbs, towing, and long trips until the fault is diagnosed. Stop if the engine misfires severely or cannot maintain safe road speed; continued poor combustion can worsen emissions and damage the catalytic converter.