U0166 — Lost Communication With Auxiliary Heater Control Module

What Does U0166 Mean?

U0166 is a diagnostic trouble code indicating: Lost Communication With Auxiliary Heater Control Module. This code relates to the network communication system. The vehicle's computer detected a condition outside normal operating parameters and stored this code.

Symptoms of U0166

⚠️ Check Engine Light (MIL) illuminated
⚠️ No communication with Auxiliary Heater Control Module
⚠️ Multiple warning lights may illuminate simultaneously
⚠️ Related system completely inoperative
⚠️ Multiple warning lights on dashboard

Common Causes

🔍 CAN bus wiring fault (open or shorted) to Auxiliary Heater Control Module
🔍 Power or ground supply issue to Auxiliary Heater Control Module
🔍 Auxiliary Heater Control Module internal failure
🔍 Water intrusion damaging module or connectors
🔍 CAN bus termination resistor fault

Frequently Asked Questions

What does U0166 mean?

U0166 indicates: Lost Communication With Auxiliary Heater Control Module. The vehicle's computer has detected that the Auxiliary Heater Control Module is not operating within its expected parameters and stored this diagnostic trouble code.

Can I drive with code U0166?

You can drive short distances for essential trips, but schedule a diagnosis soon. Driving with U0166 for extended periods may cause additional problems.

How much does it cost to fix U0166?

Repair costs for U0166 typically range from $80 to $1200, depending on the root cause. Simple wiring or connector repairs are on the lower end, while component replacement costs more. A proper diagnosis ($80–$150 at most shops) will identify the exact cause before committing to expensive parts.

What To Do Next

Possible Fixes

🔧 Inspect CAN bus wiring to Auxiliary Heater Control Module for damage
🔧 Check power and ground supply to Auxiliary Heater Control Module
🔧 Replace failed Auxiliary Heater Control Module

1
Find your vehicle above
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2
Check for recalls
Go to nhtsa.gov/recalls and enter your VIN. Free repairs if covered.
3
Get a professional diagnosis
A code alone doesn't identify the exact failed part. A diagnostic ($50–$150) pinpoints the root cause.

U0166: Lost Communication With Auxiliary Heater Control Module