P026C: Fuel Injection Quantity A Lower Than Expected

What does P026C mean?

From 2010, CARB requires diesel engines to detect when the commanded injection quantity is not delivered. The module estimates the fuel actually burned from airflow and the measured lambda (from the NOx or oxygen sensor) and corrects the quantity; if that correction passes a limit, the code sets. P026C means the engine gets less fuel than commanded. GM's 6.6 litre LML diesel checks it at idle with the vehicle stationary and the engine warm, setting it at a correction of −20 to −35 mm³ per stroke for 12 s; later GM diesels use the learned correction value (10 of 20 samples); both need two trips. FCA lists it with an injector cleaning procedure for deposits. Ford diesels do not use it. Typical causes are coked injectors, wrong airflow or lambda measurement and weak fuel supply.

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

Symptoms

• Check engine light on
• Lack of power
• Rough running or idle

Common causes

• High Injectors coked or clogged (too little flow)
• Medium Airflow or boost measurement wrong, NOx sensor lambda inaccurate
• Medium Weak low- or high-pressure supply (filter, pump, rail pressure)
• Low Fuel quality or contamination
• Low Software

Likelihood is a general estimate across vehicles; your make and model may differ.