P01CB: Cylinder 1 Injection Timing Performance - Over Retarded

What does P01CB mean?

Diesel engines must detect when fuel can no longer be injected at the correct crank angle – CARB requires this for every injector individually, hence one code per cylinder. The start of injection is not measured directly: during overrun with fuel cut-off the control module fires a tiny test injection into one cylinder (GM: about 1.5 mm³) and evaluates the resulting speed change at the crankshaft sensor. From this it learns how much extra energizing time the injector needs (Bosch calls this zero fuel calibration). This code means injector 1 needs clearly more energizing time than intended, i.e. it opens too late – GM sets it above 80 µs of extra time, after two trips. Documented users are GM's 6.6 litre Duramax (LML, L5P) and FCA's 3.0 litre EcoDiesel; Ford reports the same function under P2B11ff. Bulletins often point away from the injector: GM fixed false settings on 2020–2021 L5P trucks with new software and warns that vibration, for example from off-road tyres, disturbs the evaluation; FCA lists wrong injector correction codes, boost leaks and loose injector clamps.

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

Symptoms

• Check engine light on (after two drive cycles)
• Louder combustion noise or knocking
• Rough idle
• Possibly smoke

Common causes

• High Injector worn, coked or sticking (opens late, delivers too little)
• Medium False setting from software or vehicle vibration (e.g. off-road tyres)
• Medium Wrong injector correction code stored after an injector replacement
• Low Boost leak or loose injector clamp
• Low Contaminated fuel

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