Network, generic

U0632 Lost Communication With Fan 1

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modePossible

Many radiator fans now contain their own speed controller and take commands over LIN instead of relays. U0632 is set when fan 1 stops responding. GM (25OBDG03A, 25OBDG04B) fails it as Type B after 2.5 s without the fan's response frame and then suspends the fan speed checks P0494 and P30EE; the 2023/24 tables 23OBDG07 and 24OBDG07 allow three missed frames. Mitsubishi's 2023 Outlander PHEV assigns fan 1 to the right-hand radiator fan on LIN2 and sets the code after 2 s of failed communication. Mercedes bulletin LI20.00-P-076708 (GLC 254, GLE 167) reports the fan at full speed with a coolant warning and blames drivetrain controller software or LIN wiring; Audi bulletins for the Q7 cite chafed fan harnesses. Fans usually default to full speed.

Likely causes

Fan harness chafed or pinched near the radiator or plenum (Audi bulletins)

Fan power feed (fusible link) or ground open

Outdated software in the controller that runs the LIN bus (Mercedes PTCU)

Electronics in fan 1 failed (replaced as fan assembly)

Symptoms

Fan running continuously at full speed, loud
Check engine light and coolant warning message
On some Audi models limited engine speed or drive system fault message

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 1vehicle bus wiring

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