Powertrain, generic · Fuel and air metering

P01D9 Cylinder 8 Injection Timing Performance - Over Retarded

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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 8 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. The documented user for this cylinder is GM's 6.6 litre Duramax V8 (LML, L5P); Ford reports the same function under P2B11ff. 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, so injectors should not be replaced before that is ruled out.

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

Symptoms

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

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–900
Time0.5–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

fuel injector cylinder 8crankshaft position sensorengine control module

Related codes

P01DAP0308P2B11P01D7P01DB

References: law.cornell.edu, gsi.ext.gm.com, gsi.ext.gm.com, static.nhtsa.gov.