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U067C Lost Communication With Fan 3

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modePossible

Some engines need a third electric cooling fan, for instance for a charge-air or auxiliary radiator, and LIN lets each fan carry its own speed electronics. GM's 2025 diesel table 25OBDG04B uses U067C for cooling fan 3: the response frame CFM3_Rsp must be missing for at least 2,437.5 ms, the LIN channel enabled and battery voltage above 11 V; the code is Type B, so the MIL lights after two trips. While it is active GM suspends the fan 3 speed checks, P2CBB for running slower than modelled and P30F2/P30F3 for feedback out of range, the high limit being 4,000 rpm. On the engines of GM's 23OBDG07 and 24OBDG07 the same fan instead sets the GM-specific U112A on a third LIN line. Watch engine temperature under load.

Likely causes

LIN wire to fan 3 chafed or open

High-current supply, fuse or ground of fan 3 faulty

Fan 3 controller electronics failed

Fan connector corroded by road spray

Symptoms

Check engine light after two trips
High coolant or charge-air temperature at low speed or when towing
Fan 3 silent or running constantly

Repair estimate

DifficultyMediumWorkshop job

Parts and labour€60–800

Time0.5–3 h

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

Parts involved

cooling fan 3vehicle bus wiring

References: gsi.ext.gm.com, gsi.ext.gm.com, en.wikipedia.org.