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U0631 Lost Communication With Engine Coolant Temperature Sensor 5

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

Sensor 5 is the highest-numbered engine coolant temperature input in the J2012 list and is found only on engines that monitor many coolant zones, for example block, head, radiator outlet and separate loops. U0631 records that the controller has stopped receiving digital messages from that sensor. No manufacturer documents it publicly. Because sensor 4 and sensor 5 usually sit on different branches, U0631 on its own points to its own connector, wire or sensor electronics, while both together suggest a shared data line or supply. CARB folds sensors that watch distinct coolant loops into the cooling system monitor, so the MIL is plausible. LIN messages carry a checksum, and a sensor that answers with bad frames counts as missing too. Expect a substitute value and cautious fan control.

Likely causes

Wiring to sensor 5 damaged (open, short, chafing)
Connector at sensor 5 corroded or not latched
Sensor 5 electronics failed or sending corrupt frames
Shared supply or data line fault (often with U0630)

Symptoms

  • Check engine light
  • Fan running more often or longer

Repair estimate

DifficultyMediumDIY possible
Parts and labour€30–300
Time0.3–1.5 h

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

Parts involved

engine coolant temperature sensor 5vehicle bus wiring

Related codes

U0630P01E3P2182P0115P2181

References: law.cornell.edu, en.wikipedia.org, nxp.com.