U0685Lost Communication With Catalyst Temperature Bank 1 Sensor 2
- Generic OBD-II code · Network
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- Where a converter carries two temperature probes, one usually sits ahead of the brick and one behind it, so that the heat released by the reaction shows up as a rise between them. Sensor 2 on bank 1 is the second, downstream position. U0685 means this probe reports over a digital link and its messages no longer arrive. No manufacturer documents this code publicly, so thresholds and debounce times are unknown. Without the second reading, the comparison with sensor 1 is lost: the correlation code P046A cannot be judged, and any strategy that uses the temperature rise as a sign of catalyst activity loses its input. Analog faults of the same probe are P042A to P042D; sensor 1 has U0684. CARB requires a separate code for digital inputs that fall silent.
- What you may notice
- Check engine light
- Catalyst monitor or sensor comparison stays incomplete
- Likely causes
- LikelyLead of the downstream probe damaged by heat, stones or road salt
- PossibleSensor electronics failed
- PossibleConnector corroded or not fully latched
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €60 – €450
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.