U0633 code meaning
Lost Communication With Fan 2
Network system Generic code U06xx codes Check engine light
What U0633 means
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.
U0633 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0633
- 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
Common causes of U0633
- Most 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
- Less likelyFan 2 controller electronics failed
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Cooling fan 2Vehicle bus wiring
What each part of U0633 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 33 | The exact fault in that area. |
What to do next
- Note U0633 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U0633
What does U0633 mean?
U0633 means "Lost Communication With Fan 2". U0633 is the counterpart for a second LIN-controlled radiator fan. It is a generic code, so it means the same on every make.
Is it safe to drive with U0633?
Drive gently and only to a workshop. With U0633 the car can go into limp mode (reduced power) to protect itself.
Will U0633 fail an emissions test?
Yes, it can. U0633 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is U0633 to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will U0633 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.