U0165
- Network & Communication
- Generic (SAE)
Not urgent
Unlikely to affect driveability. Worth resolving so the light does not mask a future fault.
Lost Communication with Auxiliary HVAC Control Module
This code is in our catalogue but has not yet been through editorial review, so the guidance below is limited to what our structured data supports. We publish deeper diagnostic content only after a code has been reviewed — here is why.
The Auxiliary HVAC Control Module has stopped transmitting on the vehicle data bus, so other control units no longer receive its messages. Rear or auxiliary climate control stops working. Typical causes are loss of power or ground at the module, an open or shorted CAN/LIN bus wire, a connector fault, or an internal module failure.
A trouble code records what a control module measured. It does not identify which part failed. Test before replacing anything.
- Safe to drive
- Unlikely to affect driveability. Worth resolving so the light does not mask a future fault.
- Urgency
- Not urgent
- Will it pass emissions
- Not affected
- Check engine light
- Varies
- 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
Many vehicles show no symptom at all beyond the warning light. The absence of a symptom does not mean the fault is not real.
| # | Cause | How often | Component |
|---|---|---|---|
| 1 | Auxiliary HVAC module unpowered | Very common | — |
| 2 | CAN wiring to auxiliary HVAC broken | Common | — |
| 3 | Gateway module routing CAN messages incorrectly | Occasional | — |
Ordering reflects how often each cause is responsible in general, not a probability for your vehicle. Confirm by testing.
- HVAC Control Module
- CAN Bus Wiring
- Definition
- Generic code set (SAE J2012 / ISO 15031-6) via the OBDexopen database, dedicated to the public domain under CC0-1.0.
- Diagnostic guidance
- Written and reviewed in-house. See our editorial policy.
- Review status
- Awaiting review
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