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DTC codes / U01xx · Lost communication with a control module / U016B

U016BLost Communication With A/C Compressor Control Module

U016B is a network communication code indicating that the module responsible for controlling the air conditioning compressor has stopped reporting on the vehicle's controller area network (CAN) bus. The computer that monitors this module, typically the body control module (BCM) or powertrain control module (PCM), has detected a loss of the periodic messages it expects from the A/C compressor control module.

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

Symptoms you may notice

  • The air conditioning may blow warm air or not engage at all.
  • The A/C compressor clutch may fail to engage when requested.
  • The climate control panel may show a fault or flash indicator lights.
  • Other unrelated electrical accessories may behave erratically if the module shares a bus segment.
  • Often no symptoms besides the warning light, especially if the A/C was not in use.
  • The cooling fans may run continuously or not at all depending on default strategy.

Common causes, most likely first

  1. A blown fuse or poor connection at the A/C compressor control module power or ground circuit.
  2. Damaged, corroded, or disconnected wiring in the CAN bus circuit between the module and the network.
  3. A failed A/C compressor control module itself, often due to internal electronics or water intrusion.
  4. A weak or failing battery or charging system causing low voltage and communication dropouts.
  5. A faulty body control module or gateway module that relays messages to the A/C module.
  6. Loose or corroded connector pins at the A/C compressor control module harness.
  7. Aftermarket accessories or improper electrical repairs introducing bus interference.

How to diagnose and fix it

  1. Verify battery voltage and charging system output; low voltage is a common cause of communication codes.
  2. Check all fuses and relays related to the A/C compressor control module and climate control system.
  3. Inspect the A/C compressor control module connector and harness for corrosion, loose pins, or damage.
  4. Perform a voltage drop test on the module's power and ground circuits to confirm they are intact.
  5. Use a scan tool to check for communication on the bus and perform a network integrity test if supported.
  6. If the module is accessible, swap with a known-good unit only after confirming wiring integrity, then reprogram if required.
  7. Clear the code and road test with A/C on to verify the repair and ensure the code does not return.

Why the A/C Module Goes Silent

  • A weak battery or failing alternator often sets U016B before any A/C symptom appears, so always load-test the battery first.
  • The A/C compressor control module may be integrated into the compressor itself on some vehicles, making replacement more involved than a simple bolt-on.
  • Corrosion at the module connector is a frequent culprit, especially in areas with road salt or high humidity, and can mimic a failed module.
  • This code can be set by a gateway module that fails to relay messages, so the fault may not be at the A/C module at all.
  • After clearing the code, if it returns immediately with the key on and engine off, suspect a wiring or module power issue rather than a mechanical A/C fault.

Can I keep driving with U016B?

You can generally drive the vehicle safely with this code, but the air conditioning may not work and defogging performance could be reduced. Avoid long trips in hot weather or conditions requiring defrost until repaired, and address any low voltage issue promptly to prevent further communication faults.

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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