Powertrain, generic (extended)

P2CB9 Fan 2 Underspeed

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P2CB9 means the second electric cooling fan reports a lower speed than its command calls for, while communication and wiring are judged sound. GM uses it in two ways. In tables 23OBDG07 and 24OBDG07 the fan must stay below a speed-dependent floor of up to 3550 rpm for 20 s once it has been commanded above 7.65 % for more than 5 s. The 2025 diesel table 25OBDG04B models the expected speed of a LIN fan and flags 16 bad samples out of 20 at one per second, for example under 2300 rpm when 2500 rpm is asked for; both are two-trip codes with the lamp. GM's PIE0601 of 2020 lists P2CB9 with P0494, U0632 and U0633 on 2020–2021 full-size trucks and SUVs and asks for a look at fuses and debris in the blades. Fan 1 has P0494, overspeed of fan 2 is P2CBA.

Likely causes

Fan blades slowed by debris, leaves, snow or ice
Fan 2 motor or its integrated electronics worn or faulty
Blown fuse, weak supply or poor ground at the fan
Sporadic entry without fault found (GM investigated without a fix)

Symptoms

  • Check engine light after two trips
  • Coolant temperature rises at idle or when towing
  • Weaker air conditioning at standstill

Repair estimate

DifficultyMediumDIY possible
Parts and labour€50–900
Time0.5–4 h

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

Parts involved

cooling fan 2

Related codes

P2CBAP0494P2CBBU0633P2B31P2B32

References: gsi.ext.gm.com, gsi.ext.gm.com, static.nhtsa.gov, static.nhtsa.gov.