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U0687 Lost Communication With Catalyst Temperature Bank 2 Sensor 2

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modeNo

U0687 refers to the rear catalyst temperature probe of bank 2, the one behind the converter brick on the second cylinder row. Once its digital messages stop, the controller can no longer compare bank 2 inlet and outlet temperatures (P046B) and loses an over-temperature guard: such probes have long been used to warn when a converter runs hotter than it can tolerate, which on older two-way designs was around 750 °C. No manufacturer documents this code publicly, so MIL timing and debounce are not known; CARB only requires that silence of a digital input sets its own code. Analog faults at this point are P043A to P043D, and sensor 1 of the same bank is U0686. The car usually drives normally, but the fault should not be left, since misfires could go on overheating the converter.

Likely causes

Lead of the rear bank 2 probe damaged

Sensor electronics failed after overheating

Connector corroded

Symptoms

Check engine light
Bank 2 temperature comparison not possible
No noticeable change in driving

Repair estimate

DifficultyMediumDIY possible

Parts and labour€60–500

Time0.5–2.5 h

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

Parts involved

catalyst temp sensor bank 2 sensor 2vehicle bus wiring

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