U0686: Lost Communication With Catalyst Temperature Bank 2 Sensor 1

What it means

The vehicle bus reports loss of communication with smart catalyst temperature sensor on bank 2 sensor 1. Catalyst protection and light-off monitoring switch to model-based estimates.

At a glance

• Usually lights the warning light of the system that lost communication
• Affects emissions; the car can fail an emissions test

How it works

Catalyst temperature sensor 1 on bank 2 sends its reading over the vehicle network for catalyst protection and light-off monitoring. This code sets when messages from bank 2 sensor 1 are lost, so the controller may use an estimated temperature for that catalyst.

Common causes

Most likely first.

1. Bus wiring open or shorted
2. Module without power or ground
3. Module failed

Symptoms

• Multiple warning lights may illuminate
• Affected modules may go into limp mode or shut down
• Specific functions inoperative depending on module
• Diagnostic tools may show communication faults

How to diagnose it

1. Save freeze-frame data and scan all modules for communication codes to determine whether bank 2 sensor 1 alone is affected.
2. Check live data for bank 2 sensor 1 temperature and communication status, comparing it with bank 2 sensor 2 and available bank 1 readings.
3. Inspect bank 2 sensor 1's connector and bus wiring near the exhaust for heat damage, abrasion, corrosion, or loose pins.
4. Verify power and ground at the sensor or module using the manufacturer's procedure.
5. Test the bank 2 sensor 1 bus branch for opens or shorts, then evaluate the sensor or module if the circuit and supplies are sound.

Common fixes

• Reconnect or clean the bank 2 sensor 1 connector.
• Repair heat-damaged bus wiring or terminals for bank 2 sensor 1.
• Fix a missing power or ground connection to the sensor or module.
• Replace bank 2 sensor 1 or its module if testing isolates an internal failure.

Can I keep driving?

If the engine runs normally, a short, gentle trip may be possible, but catalyst protection and monitoring may use an estimate for bank 2. Avoid hard acceleration or towing until the fault is checked, and stop if drivability worsens.