U0643 is a network communication code indicating the engine control module (or other master module) has stopped receiving messages from the turbocharger/supercharger temperature sensor module over the vehicle's data bus. It does not mean the air charge is too hot or too cold — it means the two modules are no longer talking, so temperature readings from that sensor are unavailable.
Heat, vibration, and oil exposure near the turbo make the harness and connector the single most common failure point. Broken wires, chafed insulation, or pushed-out pins interrupt the bus signals.
The sensor itself contains a small electronic module that transmits on the data bus. Internal failure of that module is a common root cause once the harness has been ruled out.
If the sensor module loses its 5 V reference or chassis ground, it cannot transmit on the bus, which is reported as lost communication rather than an out-of-range reading.
A short to voltage, short to ground, or high-resistance connection on the communication pair can knock the sensor module off the bus.
Some manufacturers have released updated PCM or sensor module calibrations that resolve U0643, particularly when the sensor module boots but does not handshake correctly.
Rare, but a damaged transceiver in the PCM can stop communication with this specific module. This should only be considered after every other cause has been excluded.
Usually the vehicle can be driven, but boost may be limited or the turbocharger protection strategy may be disabled, which can allow overheating under heavy load. Limit aggressive driving and address it promptly.
Almost never. U0643 is a network communication code, and the failed component is typically the sensor module, its harness, or its power/ground — not the engine computer. Replacing the PCM for this code is one of the most common and most expensive misdiagnoses.
Clearing the code does not repair the underlying problem. If the sensor module truly is off the network, the code will return immediately, and any associated limp-mode or boost-limiting behavior will not be resolved.
No. U0643 specifically means the temperature sensor module is not communicating on the data bus. A code indicating actual over-temperature would be a different, sensor-rationality or threshold code.