U0686 code meaning

What U0686 means

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.

U0686 at a glance

• Check engine lightYes, usually on
• Emissions testCan fail
• Limp modeNot expected
• Repair difficultyMedium, DIY possible
• Typical labor0.5 to 2.5 hours
• Clears after repairWhen cleared with a scanner

Symptoms of U0686

• Check engine light
• Catalyst monitor for bank 2 not completed

Common causes of U0686

• Most likelySensor electronics on bank 2 damaged by heat
• PossibleHarness on the bank 2 side chafed or melted
• PossibleConnector corroded
• Less likelyEngine controller input fault

Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.

Parts involved

Catalyst temp sensor bank 2 sensor 1Vehicle bus wiring

What each part of U0686 means

What to do next

• Note U0686 and any other codes stored with it: several codes together often point to one cause.
• Check for loose connectors and damaged wiring around the parts the code names.
• Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
• Clear the code only after the repair. If it comes back, the fault is still there.

Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.

Codes often seen with U0686

• U0684 Lost Communication With Catalyst Temperature Bank 1 Sensor 1
• U0687 Lost Communication With Catalyst Temperature Bank 2 Sensor 2
• P0435 Catalyst Temperature Sensor Circuit Bank 2 Sensor 1
• P0436 Catalyst Temperature Sensor Circuit Range/Performance Bank 2 Sensor 1
• P0437 Catalyst Temperature Sensor Circuit Low Bank 2 Sensor 1
• P0438 Catalyst Temperature Sensor Circuit High Bank 2 Sensor 1
• P046B Catalyst Temperature Sensor 1/2 Correlation Bank 2

Questions about U0686

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