Network, generic

U0633 Lost Communication With Fan 2

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

U0633 is the counterpart for a second LIN-controlled radiator fan. GM's 2025 table 25OBDG04B checks the frame CFM2_RSP and fails after 2.5 s of silence as Type B; 23OBDG07 and 24OBDG07 count three missing frames, and on those engines fans 3 and 4 have their own codes on another LIN line. In the Outlander PHEV 2023 Mitsubishi's fan 2 is the left-hand unit. Audi bulletin 2072000/1 for the 2020-24 Q7, Q8 and RS Q8 family lists U0633 with fan circuit codes and the warning of limited performance with engine speed capped at 2000 rpm; the harness rubs on the right front frame rail. GM bulletin 23-NA-102 finds it on the Duramax 3.0 together with other LIN devices. Fan 2 alone failing while fan 1 still answers points to its own branch or motor.

Likely causes

Fan 2 harness rubbing on the frame rail or radiator support
Loose or corroded fan 2 connector
Power feed or ground of fan 2 interrupted
Fan 2 controller electronics failed

Symptoms

  • Remaining fan runs at full speed or noise from the fan area
  • Warning lamp; on Audi models limited performance and engine speed
  • Rising coolant temperature in slow traffic

Repair estimate

DifficultyMediumDIY possible
Parts and labour€50–1,200
Time0.5–3 h

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

Parts involved

cooling fan 2vehicle bus wiring

Related codes

U0632U067DP0481P0693P0694

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