The Engine Control Module (ECM) has lost communication with the catalyst temperature sensor for bank 2, sensor 2. This sensor monitors exhaust temperature after the catalytic converter on the engine bank opposite cylinder #1. The code indicates a network communication fault, not a sensor performance issue.
The sensor itself may have an internal electronic failure preventing communication with the ECM.
Poor connection at the sensor due to moisture, dirt, or physical damage can interrupt the communication signal.
Wiring harness issues such as broken wires or short circuits on the LIN bus or other communication line can cause lost communication.
The sensor may not power up if the supply voltage or ground circuit is open, preventing communication.
In rare cases, the ECM may have an internal communication failure, but this should only be considered after all other causes are ruled out.
Generally, yes. The vehicle may operate normally, but the check engine light will remain on and emissions monitors may not complete. If other symptoms appear, have the vehicle inspected.
It depends on your skill level and the sensor's location. The sensor is often accessible, but proper diagnosis is critical to avoid replacing a good sensor. Always check wiring and connectors first.
No, the ECM is rarely the cause. Many drivers are incorrectly told to replace the ECM for U0687. The problem is almost always the sensor, its connector, or the wiring. Only consider the ECM after all other possibilities are exhausted.
Bank 2 refers to the side of the engine that does not contain cylinder #1. On V-type engines, it is the opposite bank. On inline engines, there is only one bank, so a bank 2 code may indicate a misconfiguration or a specific sensor location.