Powertrain, generic (extended)

P2CBB Fan 3 Underspeed

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P2CBB concerns vehicles with three electric radiator fans: the third one turns slower than modelled for its command. GM's 2025 diesel table 25OBDG04B describes the check for a LIN-controlled fan 3. The controller converts the request into an expected speed, allows for start-up and ramp delays and for supply voltage, and compares the reported speed with a lower limit; at a 925 rpm request the floor is 725 rpm, at 2800 rpm it is 2600 rpm. Sixteen failures in twenty one-second samples set a Type B code, two trips to the lamp. The test only runs above 875 rpm and is blocked while U067C or the out-of-range fan 3 codes are active. Not every GM triple-fan setup uses P2CBB: table 23OBDG07 logs fan 3 underspeed under its own code P14D7. Overspeed is P2CBC, fan 2 underspeed P2CB9.

Likely causes

Fan 3 slowed by debris, ice or a distorted shroud
Fan 3 motor bearings or integrated controller worn
Voltage drop on the fan 3 power feed or ground

Symptoms

  • Check engine light after two trips
  • Engine runs warmer under high load or in heat
  • Reduced A/C cooling at low speed

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–1,600
Time0.5–9 h

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

Parts involved

cooling fan 3

Related codes

P2CBCP2CB9U067CP2C41P0494

References: gsi.ext.gm.com, gsi.ext.gm.com, law.cornell.edu.