U01B5: Lost Communication With Catalyst Heater Control Module

What it means

Communication with the Catalyst Heater Control Module was not received as expected. A communication fault may prevent the catalyst heater system from operating as intended.

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 Catalyst Heater Control Module manages or reports operation of the catalyst heating system, which helps the catalyst reach effective operating conditions. This code sets when expected messages from that module are missing, potentially preventing the heater system from operating as intended.

Common causes

Most likely first.

1. Module unpowered
2. Gateway module routing CAN messages incorrectly
3. CAN terminating resistor (120 Ω) drifted out of spec

Symptoms

• Multiple warning lights may illuminate
• Affected modules may go into limp mode or shut down
• Specific functions inoperative depending on module
• Diagnostic tools may show communication faults

How to diagnose it

1. Scan all modules and save freeze-frame data to see whether the catalyst heater communication fault coincides with other emissions or network codes.
2. Check whether the Catalyst Heater Control Module responds to a scan tool and whether heater status data is available.
3. Inspect the module's connectors and wiring for damage, corrosion, looseness, or heat exposure.
4. Check the module's power and ground circuits against the manufacturer's specification.
5. If supplies are sound, test the applicable network wiring and gateway routing before replacing the module.

Common fixes

• Reconnect or repair a loose or corroded module connector.
• Repair heat-damaged wiring or restore the module's power and ground.
• Repair a confirmed communication or gateway routing fault.
• Replace the Catalyst Heater Control Module if testing confirms it has failed.

Can I keep driving?

The fault can impair emissions control and may keep the check-engine light on, though it does not necessarily make the vehicle unsafe to drive. Limit unnecessary trips and address it soon, particularly if other engine warnings or poor running occur.