U0689 indicates the powertrain control module (PCM) has stopped receiving data from the turbocharger or supercharger B temperature sensor, which is typically a digitally-communicating device on a serial bus. This is a network communication fault rather than a performance-range fault, meaning the sensor or its wiring has failed to transmit a signal, not necessarily that the temperature reading is implausible.
The communication lines (often LIN or CAN) or power/ground circuits to the sensor are the most common failure points due to heat cycling, chafing near the turbocharger, or corrosion in connectors.
The sensor itself may have an internal communication circuit failure, preventing it from responding to the PCM’s requests while the actual thermistor portion may still function.
High under-hood temperatures and vibration can cause terminal fretting, back-out, or oxidation in the sensor’s multi-pin connector, interrupting the serial data line.
A blown fuse, corroded ground eyelet, or voltage drop on the sensor’s reference power supply will silence the module and set this code.
Non-OEM lighting, audio, or telematics devices tapped into shared communication buses can corrupt or block messages to the PCM.
Although rare, a failed transceiver circuit inside the PCM can cause it to stop communicating with this specific sensor while other modules function normally; this should only be considered after wiring and sensor are verified good.
No. U0689 specifically flags a data-link failure, not a mechanical turbo fault. The turbo itself may be mechanically fine; the engine computer simply cannot read its temperature sensor.
Usually not. The vast majority of U0689 faults are resolved by repairing wiring or replacing the sensor module. PCM failure is statistically unlikely and should only be diagnosed after the sensor, connectors, and harness are proven fault-free.
'B' typically indicates the secondary sensor in a dual-turbo setup, the sensor on bank 2, or a specific redundant sensor depending on the manufacturer’s topology; consult the wiring diagram to identify its physical location.
Short trips are generally safe, but the engine will likely operate in a conservative 'limp' mode to protect against over-boost or over-temperature conditions. Prolonged high-load driving should be avoided until repairs are made.