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DTC codes / U01xx · Lost communication with a control module / U0118

U0118Lost Communication with Cabin Air Quality Sensor Module

U0118 indicates that the vehicle's primary communication network has lost contact with the cabin air quality sensor module, which monitors airborne contaminants and humidity to optimize climate control and air recirculation. The body control module or climate control module has stopped receiving the periodic status messages it expects from that sensor over the data bus, setting the code after a timeout period.

SystemNetwork
Code typeGeneric (all makes)
SeverityLow
Fix difficultyIntermediate
AreaLost communication with a control module

Symptoms you may notice

  • Often no symptoms besides the warning light, because the climate system defaults to a fixed recirculation strategy
  • Automatic air recirculation may stop switching to recirculate when outside air quality is poor
  • Climate control may stay in fresh-air mode constantly or default to recirculation regardless of conditions
  • A slight delay or lack of response when pressing the recirculation button on some vehicles
  • Other unrelated warning lights or communication codes may appear if the fault is a bus wiring issue

Common causes, most likely first

  1. Failed cabin air quality sensor module, often due to contamination or internal electronics failure
  2. Open or shorted wiring in the dedicated communication bus between the sensor and the control module
  3. Corroded or loose connector pins at the sensor or at the climate control module
  4. Blown fuse or poor ground connection serving the sensor module
  5. Water intrusion or debris blocking the sensor's sampling port, causing it to shut down
  6. A faulty body control module or climate control module that is not polling the sensor correctly
  7. Aftermarket accessories or poor previous repairs disturbing the bus wiring

How to diagnose and fix it

  1. Use a scan tool to confirm U0118 is current and check for other communication codes on the same bus
  2. Inspect the cabin air quality sensor connector and wiring for corrosion, looseness, or damage
  3. Check the fuse and ground circuit for the sensor module with a multimeter
  4. Measure bus voltage or resistance at the sensor connector to verify the communication line is intact
  5. Substitute a known-good sensor or perform a bidirectional test if the scan tool supports it
  6. Repair or replace damaged wiring and clear the code to see if it returns
  7. If wiring and power are good, replace the cabin air quality sensor module and recheck communication

What most technicians miss on U0118

  • A dirty or obstructed cabin air quality sensor is a common cause that many people overlook, because the sensor can stop communicating when its sampling chamber is clogged with dust or debris.
  • U0118 does not always mean the sensor itself has failed; a single chafed wire or a poor ground can set the same code, so voltage-drop testing at the connector is essential before replacing parts.
  • On some vehicles the cabin air quality sensor shares a bus with other body modules, so a fault elsewhere on that bus can masquerade as a sensor communication loss.
  • After replacing the sensor, some vehicles require a relearn or initialization procedure with a scan tool before the code will clear and stay cleared.
  • A weak or failing battery can cause intermittent communication codes like U0118, especially if the code appears only after a cold start or long sit.

Can I keep driving with U0118?

This code is safe to drive with because it only affects climate control convenience features and does not impair engine, braking, or steering systems. You can continue driving, but have the fault diagnosed when convenient to restore proper automatic air recirculation and air quality management.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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