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DTC codes / U06xx · Network communication / U0686

U0686Lost Communication With Catalyst Temperature Bank 2 Sensor 1

U0686 is a network communication fault indicating that a control module on the vehicle's Controller Area Network (CAN) bus has lost contact with the catalyst temperature sensor for bank 2, sensor 1. The computer detected that the expected periodic message from that sensor or its interface module stopped arriving within the required time window, so it flagged the missing communication rather than a direct temperature reading error.

SystemNetwork
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaNetwork communication

Symptoms you may notice

  • Illumination of the malfunction indicator lamp (check engine light) with no other obvious dashboard warnings.
  • Often no symptoms besides the warning light, especially if the sensor's data is not critical to immediate engine operation.
  • Rough running or reduced fuel economy if the powertrain control module substitutes a default catalyst temperature value.
  • A stored pending or history code that returns after clearing, sometimes intermittently.
  • Other communication-related codes appearing in modules that share the same CAN bus segment.
  • Possible limp-home mode or reduced power if the missing data affects emissions control strategy.

Common causes, most likely first

  1. Damaged, corroded, or disconnected wiring or connector pins at the bank 2 sensor 1 catalyst temperature sensor.
  2. Open or shorted sensor signal circuit between the sensor and its control module.
  3. Failed catalyst temperature sensor itself, causing it to stop transmitting data.
  4. Faulty control module or interface module that relays the sensor data onto the CAN bus.
  5. CAN bus wiring fault such as a rubbed-through harness, loose ground, or water intrusion in a connector.
  6. Low battery voltage or charging system problem that disrupts module communication.
  7. Aftermarket accessories or poor previous repairs that disturb the network wiring.

How to diagnose and fix it

  1. Connect a scan tool and record all stored, pending, and history codes across every module to confirm U0686 is active and not a ghost code.
  2. Inspect the bank 2 sensor 1 catalyst temperature sensor connector and harness for corrosion, looseness, chafing, or water intrusion.
  3. Check battery voltage and charging system output, then clear codes and verify whether U0686 returns immediately.
  4. Measure resistance and voltage on the sensor signal circuit according to the manufacturer's wiring diagram to rule out an open or short.
  5. Substitute a known-good sensor or signal simulator at the connector to see if communication restores on the scan tool.
  6. Inspect the CAN bus wiring and grounds for the module that interfaces with the sensor, looking for rub-throughs or loose terminals.
  7. If wiring and sensor test good, follow the manufacturer's diagnostic flow for the control module and network integrity before replacing any module.

Why this code is often a wiring fault

  • U0686 is frequently set by a poor connection at the sensor pigtail rather than a failed sensor, so wiggle-testing the harness while watching live data can reveal the fault.
  • A weak or failing battery can cause multiple U-codes including U0686 because modules drop offline during cranking, and the code may never return after charging or replacement.
  • Technicians sometimes replace the catalyst temperature sensor only to find the real problem is a chafed CAN wire near the exhaust or transmission, so always inspect the full circuit.
  • This code does not mean the catalytic converter itself has failed; it only reports lost communication with the temperature sensor, and converter replacement based on U0686 alone is a misdiagnosis.
  • Aftermarket remote starters or alarm installations that tap into network wiring are a commonly overlooked cause of intermittent U0686 and similar communication codes.

Can I keep driving with U0686?

The vehicle is generally safe to drive short distances because the fault is a communication loss rather than a mechanical failure, but avoid long trips or heavy load until diagnosed. If the check engine light flashes or the engine runs poorly, stop driving and have the circuit inspected promptly.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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