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U0689 Lost Communication With Turbocharger/Supercharger B Temperature Sensor

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

Twin-charger engines may monitor a temperature at the second charger, for instance to protect the compressor or turbine of charger B from overheating; CARB's diesel data list includes compressor inlet as well as turbine inlet and outlet temperatures. U0689 means the reading of the temperature sensor for charger B arrives over a digital link and that link has failed. Such a channel can be built into a combined pressure sensor, as Infineon's KP276 shows with its SENT-transmitted NTC input. No manufacturer documents U0689 publicly, and none of the Ford or GM summaries examined contains it. Circuit faults of an analog sensor are P2B8F to P2B92, charger A's link loss is U0643. With the value gone, the controller may protect the charger by limiting boost.

Likely causes

Wiring near charger B damaged by heat
Connector loose or corroded
Temperature sensor or its interface electronics failed

Symptoms

  • Check engine light
  • Boost reduced as a precaution
  • Otherwise often unchanged driving

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–500
Time0.5–2 h

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

Parts involved

turbo b temp sensorvehicle bus wiring

Related codes

U0643P2B8FP2B90P2B91P2B92

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