P01CB: Cylinder 1 Injection Timing Performance

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.

Medium severity. Can I keep driving?Drive as little as possible and go to a repair shop. If you smell fuel or the engine is shaking badly, do not keep driving.

Cylinder 1 is numbered according to the manufacturer: check your engine's manual before working on it.

Symptoms

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

Most likely causes

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

What to check, in order

Start with the simplest. You can tick off each step.

Check the connector and wiring of the injector indicated
Compare the reading with other engine data while varying the engine speed.
Measure the resistance and compare it with the manufacturer's specification
Check the control signal with an oscilloscope; on direct injection or diesel engines, leave this to a repair shop because of the high voltages
On diesels, check the per-cylinder injection corrections

Good to know

Repair difficulty: hard
It affects emissions.

What each character of P01CB means

P: Powertrain: engine and transmission
0: Generic code: same on every make
1: Air and fuel
CB: Specific fault in that system

Frequently asked questions

Can I keep driving with code P01CB?

Drive as little as possible and go to a repair shop. If you smell fuel or the engine is shaking badly, do not keep driving.

What causes code P01CB?

The most common causes are: injector worn, coked or sticking (opens late, delivers too little); false setting from software or vehicle vibration (e.g. off-road tyres); wrong injector correction code stored after an injector replacement.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.

P01CB: Cylinder 1 Injection Timing Performance - Over Retarded