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U0686 Lost Communication With Catalyst Temperature Bank 2 Sensor 1

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modeNo

Bank 2 exists only on engines whose cylinder rows feed separate exhaust paths, so U0686 belongs to V or flat engines with one converter per side. It means the first catalyst temperature probe of that second bank has stopped delivering digital messages. Such probes are often a thermocouple paired with a small electronics unit; Sensience, for example, sells N-type probes rated to 1000 °C whose module converts the reading to SENT or CAN. The module and its lead sit close to hot exhaust parts, which makes heat damage a typical cause. None of the carmakers describes this code in public material. The analog equivalents are P0435 to P0438; the same position on bank 1 is U0684. CARB requires a dedicated code once a digital input goes mute.

Likely causes

Sensor electronics on bank 2 damaged by heat

Harness on the bank 2 side chafed or melted

Connector corroded

Engine controller input fault

Symptoms

Check engine light
Catalyst monitor for bank 2 not completed

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 1vehicle bus wiring

References: sensience.com, law.cornell.edu.