U0685 code meaning
Lost Communication With Catalyst Temperature Bank 1 Sensor 2
Network system Generic code U06xx codes Check engine light
What U0685 means
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.
U0685 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 2 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0685
- Check engine light
- Catalyst monitor or sensor comparison stays incomplete
Common causes of U0685
- Most likelyLead of the downstream probe damaged by heat, stones or road salt
- PossibleSensor electronics failed
- PossibleConnector corroded or not fully latched
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 1 sensor 2Vehicle bus wiring
What each part of U0685 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 85 | The exact fault in that area. |
What to do next
- Note U0685 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.
Questions about U0685
What does U0685 mean?
U0685 means "Lost Communication With Catalyst Temperature Bank 1 Sensor 2". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with U0685?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will U0685 fail an emissions test?
Yes, it can. U0685 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is U0685 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will U0685 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.