U0687Lost Communication With Catalyst Temperature Bank 2 Sensor 2
- Generic OBD-II code · Network
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- U0687 refers to the rear catalyst temperature probe of bank 2, the one behind the converter brick on the second cylinder row. Once its digital messages stop, the controller can no longer compare bank 2 inlet and outlet temperatures (P046B) and loses an over-temperature guard: such probes have long been used to warn when a converter runs hotter than it can tolerate, which on older two-way designs was around 750 °C. No manufacturer documents this code publicly, so MIL timing and debounce are not known; CARB only requires that silence of a digital input sets its own code. Analog faults at this point are P043A to P043D, and sensor 1 of the same bank is U0686. The car usually drives normally, but the fault should not be left, since misfires could go on overheating the converter.
- What you may notice
- Check engine light
- Bank 2 temperature comparison not possible
- No noticeable change in driving
- Likely causes
- LikelyLead of the rear bank 2 probe damaged
- PossibleSensor electronics failed after overheating
- RareConnector corroded
- 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 – €500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.