U0621 indicates that the powertrain control module (PCM) has lost communication with the exhaust gas temperature (EGT) sensor located in Bank 2, Sensor 1. This typically points to a wiring, connector, or sensor fault rather than a PCM failure.
The most common cause is a broken wire, chafed insulation, or corrosion at the EGT sensor connector, especially near the exhaust where heat and moisture are present.
The sensor itself may have failed internally, causing an open circuit or short that prevents communication with the PCM.
A loose or corroded pin at the PCM connector for the EGT sensor circuit can interrupt communication.
Physical damage to the sensor or its wiring from road debris, or aftermarket exhaust modifications that relocated or removed the sensor, can cause loss of communication.
Though rare, a PCM issue such as corrupted software or a failed internal driver can cause this code. This should only be considered after thoroughly checking wiring and the sensor.
Almost never. The PCM is the last thing to suspect. In the vast majority of cases, the problem is a damaged wire, corroded connector, or a failed EGT sensor. Replacing the PCM without proper diagnosis is wasteful and usually does not fix the code.
You may be able to drive short distances, but the PCM may limit engine power or disable certain emissions systems. Prolonged driving could lead to reduced fuel economy or, in diesel engines, issues with DPF regeneration. It's best to diagnose and repair promptly.
Bank 2 refers to the cylinder bank that does not contain cylinder #1 (on V6/V8 engines). Sensor 1 is the first exhaust gas temperature sensor after the exhaust manifold, typically located before the catalytic converter or diesel particulate filter.
No. Clearing the code only turns off the Check Engine Light temporarily. If the underlying issue (e.g., a broken wire) is not repaired, the code will return, often within a few drive cycles.