Powertrain, generic (extended)

P2BB2 Alternative Fuel Tank Empty

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

P2BB2 reports that the tank for the second fuel, mostly CNG or LPG, has been drawn down to its usable minimum. It is a status message rather than a component fault: a bi-fuel vehicle simply goes back to petrol. GM's bulletins for its bi-fuel models show the logic: the ECM derives the gas level from the tank pressure sensor, the 2013 Silverado and Sierra 2500HD gauge reads empty at roughly 500 psi and the 2015 Impala at about 400 psi, and when the gas is used up the engine changes to petrol on its own; GM's documents name no DTC for this step. No maker documents P2BB2 openly. If it appears with a full tank, suspect the tank pressure or level sensor (P019E, P01AF) or a closed tank shutoff valve (P224C). CARB treats such engines as alternate-fueled vehicles.

Likely causes

Gas tank actually used up to its reserve
Tank pressure or level sensor reading too low
Tank shutoff valve closed or not opening

Symptoms

  • Engine runs on petrol only, gas mode cannot be selected
  • Gas gauge shows empty or low-level warning

Repair estimate

DifficultyEasyDIY possible
Parts and labour€0–300
Time0–1.5 h

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

Parts involved

alt fuel tankalt fuel level sensor

Related codes

P2BB0P2BB1P019EP01AFP224C

References: law.cornell.edu, static.nhtsa.gov, static.nhtsa.gov.