U0633Lost Communication With Fan 2
- Generic OBD-II code · Network
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- 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.
- What you may notice
- 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
- Likely causes
- LikelyFan 2 harness rubbing on the frame rail or radiator support
- PossibleLoose or corroded fan 2 connector
- PossiblePower feed or ground of fan 2 interrupted
- RareFan 2 controller electronics failed
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €50 – €1,200
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.