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Home / DTC / U0165 — Lost Communication With HVAC Control Module - Rear

U0165 — Lost Communication With HVAC Control Module - Rear

Detailed page for trouble code U0165.

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10,562generic
22,461specific
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Code

U0165

Generic U — Network/User

Lost Communication With HVAC Control Module - Rear

Brand: Generic
Type: U — Network/User
Views: UK: 17 EN: 23 RU: 18
AI status
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Page language: EN

Causes

  • Rear HVAC control module not powered or grounded
  • Loose, corroded or disconnected connector at the rear HVAC module
  • Damaged or shorted wiring on the network (CAN/LIN) or to the module
  • Failed rear HVAC control module
  • Faulty vehicle communication bus (open, short, missing termination, or high noise)
  • Faulty gateway/module that routes messages between networks

Symptoms

  • Rear HVAC controls inoperative or not responding
  • Driver information message or warning indicating 'Service HVAC' or 'Rear Climate Fault'
  • No rear temperature/vent status displayed in infotainment or cluster
  • Loss of some climate functions while front HVAC may still operate
  • Intermittent or permanent fault lamp depending on system

What to check

  • Verify DTC present and check freeze frame / related U or B codes with a scan tool
  • Perform a visual inspection of rear HVAC module connector and harness for damage, corrosion or moisture
  • Check fuses and power/ground circuits for the rear HVAC module
  • Use a scan tool to request module identity and presence on the network
  • Monitor vehicle network traffic for messages from the rear HVAC module
  • Inspect gateway or junction modules that link the rear HVAC network to the rest of the vehicle

Signal parameters

  • Module presence/identity on network: acknowledgement/response to diagnostic addressing
  • Network message activity: frequency of HVAC-related CAN/LIN frames and message IDs
  • CAN/LIN bus physical layer: CAN_H/CAN_L waveforms or LIN data pulses and noise
  • Supply voltage to module (battery voltage when key on) and key-switched power feed
  • Module ground continuity to chassis ground
  • Bus termination resistance and continuity across network ends

Diagnostic algorithm

  1. Read and record the U0165 DTC and any related codes from all modules. Note freeze frame data and occurrence (current vs. intermittent).
  2. Visually inspect the rear HVAC module connector, harness, and nearby components for damage, corrosion, moisture or loose pins. Repair as needed.
  3. Verify power and ground at the rear HVAC module connector with the key in the appropriate position. Check module fuses and associated relay circuits.
  4. Using a scan tool, attempt to communicate with the rear HVAC module. If the tool cannot address the module, confirm whether other modules on the same bus respond.
  5. Monitor the vehicle network (CAN/LIN) with a scan tool or scope. Look for the expected HVAC message IDs or periodic frames and check for bus noise or missing messages.
  6. If no messages from the rear HVAC module, backprobe the module connector to verify supply voltage and ground while observing for intermittent faults (wiggle test harness).

Likely causes

  • Blown fuse or disconnected power/ground to the rear HVAC module
  • Loose or corroded connector at the rear HVAC module
  • Intermittent wiring fault on the local network (broken wire, pinched harness)
  • Faulty gateway or central gateway preventing forwarding of rear HVAC messages

Fault status

⚠️ Status
Stored when the rear HVAC control module does not respond on the vehicle communication network within expected time-outs. May be current or intermittent depending on whether the module is intermittently present on the bus.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

U0100 U0121 U0144 U0155 U0161 U0162
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