U0643: Lost Communication With Turbocharger/Supercharger A Temperature Sensor

What it means

A control module has stopped receiving expected network messages from the turbocharger/supercharger A temperature sensor. The effect on temperature monitoring and engine operation depends on the vehicle's system design.

At a glance

• Usually lights the warning light of the system that lost communication
• Affects emissions; the car can fail an emissions test

How it works

The turbocharger/supercharger A temperature sensor reports temperature information over the vehicle network for the forced-induction system. A control module sets U0643 when expected messages from this specific sensor stop arriving; temperature readings may then be missing or unusable.

Common causes

Most likely first.

1. Bus wiring open or shorted
2. Module without power or ground
3. Module failed

Symptoms

• Warning light or message related to the affected system
• Temperature data may be unavailable

How to diagnose it

1. Use a scan tool to record freeze-frame data and check which modules report U0643, along with any related communication or temperature-sensor codes.
2. Check live data for the turbocharger/supercharger A temperature reading and confirm whether it is absent or marked invalid.
3. Inspect the sensor module’s connectors and accessible network wiring for looseness, corrosion, chafing, or damage.
4. Check the sensor module’s power and ground circuits against the manufacturer’s specification.
5. Test the relevant network bus wiring for an open or short, following the vehicle wiring information.
6. If wiring, power, and ground pass, verify the network signals and module operation before considering sensor-module replacement.

Common fixes

• Reconnect or clean a loose or corroded connector at the temperature-sensor module.
• Repair damaged network wiring to the turbocharger/supercharger A temperature sensor.
• Restore a missing power or ground supply to the sensor module.
• Replace the failed sensor module if its circuits and network connection are sound.

Can I keep driving?

If the vehicle runs normally and has no overheating or boost warning, a short, gentle trip to a repair location may be reasonable. Avoid hard acceleration or towing until temperature monitoring is restored, and stop if an overheating warning appears.