Network, generic

U0649 Lost Communication With Coolant Pump D

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modeNo

Coolant pump D is the fourth auxiliary electric pump in the generic lettering that runs from A (U0623) through B and C (U0624, U062F) to E (U0698). What D circulates is up to the manufacturer; GM, for example, assigns C to its low-temperature loop, while Mercedes uses the E code for a pump of its low-temperature circuit. U0649 is set when pump D, controlled over LIN or a similar link, no longer sends a response. No manufacturer documents U0649 publicly. Pumps of this kind receive speed commands over LIN or PWM and report their own diagnosis, as Bosch describes for the PDE. Its circuit and internal faults are P2B66 to P2B6C, with P2C49 and P2BA1 for performance and underspeed. Loss of the pump leaves its loop without circulation.

Likely causes

LIN, supply or ground wire to pump D damaged

Corroded pump D connector

Pump D electronics failed

Controller acting as LIN master faulty or needing a software update

Symptoms

Warning lamp, depending on manufacturer the MIL
Components on the affected loop run warmer than normal

Repair estimate

DifficultyMediumWorkshop job

Parts and labour€50–800

Time0.3–2.5 h

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

Parts involved

coolant pump dvehicle bus wiring

References: law.cornell.edu, bosch-mobility.com, static.nhtsa.gov.