U0630: Lost Communication With Engine Coolant Temperature Sensor 4

What it means

A control module has stopped receiving expected network messages from engine coolant temperature sensor 4. The effect on engine temperature monitoring and control 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

Engine coolant temperature sensor 4 reports temperature information through a networked module on vehicles equipped with this sensor arrangement. U0630 sets when expected messages from sensor 4 stop reaching a receiving module, leaving that temperature input unavailable or unreliable.

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
• Engine temperature data may be unavailable

How to diagnose it

1. Record freeze-frame data and scan all modules for related network, temperature-sensor, or power-supply codes.
2. Check live data for engine coolant temperature sensor 4 and compare it with other available temperature readings when the engine is cold and warming up.
3. Inspect sensor 4's network wiring and connectors for chafing, corrosion, loose terminals, or water intrusion.
4. Verify power and ground at the module that communicates sensor 4, following the wiring diagram and manufacturer's specifications.
5. Check the network circuit for opens or shorts using the manufacturer's procedure, then evaluate the sensor's communicating module if the circuit and supplies are sound.

Common fixes

• Repair damaged wiring or loose terminals on the sensor 4 communication path.
• Clean or replace corroded connectors and restore connector seals.
• Repair a failed power or ground connection at the module serving sensor 4.
• Replace the sensor 4 communicating module only after its wiring, power, and ground have been verified.

Can I keep driving?

A missing sensor 4 reading can reduce the accuracy of engine temperature monitoring, even if another sensor still reports temperature. Avoid hard use and stop if the temperature warning appears or the engine overheats; inaccurate temperature information can delay a warning or affect engine control.