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DTC codes / U01xx · Lost communication with a control module / U01BC

U01BCLost Communication With Charge Air Cooler Coolant Pump B

U01BC is a generic communication fault indicating that a control module on the vehicle's network has lost contact with the charge air cooler (CAC) coolant pump B, which is the electric pump that circulates coolant through the air-to-liquid intercooler circuit. The module that monitors this pump—typically the engine control module (ECM) or a dedicated pump controller—has stopped receiving expected status messages or electrical feedback from the pump over the controller area network (CAN) or a dedicated serial link.

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

Symptoms you may notice

  • Illumination of the check engine light or a specific service warning for the charge air cooler system
  • Reduced engine power or a limp-home mode triggered by the ECM when intake air temperature rises
  • Poor acceleration or sluggish throttle response, especially during sustained boost or towing
  • A noticeable drop in fuel economy as the ECM richens the mixture to protect the engine
  • Often no symptoms besides the warning light, particularly if the pump only fails intermittently
  • In rare cases, elevated intake air temperature readings visible on a scan tool live data stream

Common causes, most likely first

  1. Failed charge air cooler coolant pump B, typically due to a seized motor, worn brushes, or a failed internal control circuit
  2. Blown fuse or tripped relay in the pump's dedicated power circuit
  3. Damaged, corroded, or disconnected electrical connector at the pump or along the harness
  4. Open or shorted wire in the pump's power, ground, or communication circuit
  5. Low coolant level or air lock in the charge air cooler circuit causing the pump to overheat and shut down
  6. Failed pump control module or a software fault in the module that communicates with the pump
  7. Corrosion or water intrusion in the pump connector, common on vehicles driven in wet or salty conditions

How to diagnose and fix it

  1. Scan all modules for stored and pending codes, then verify the U01BC is current and not a history code from a previous repair
  2. Check the pump's fuse and relay, and confirm battery voltage and ground at the pump connector with the key on
  3. Inspect the pump connector and harness for corrosion, chafing, or loose pins, and perform a wiggle test while watching live data
  4. Command the pump on with a scan tool and listen for operation; measure current draw with a clamp meter to confirm the motor is not seized
  5. Check coolant level and bleed the charge air cooler circuit according to the manufacturer's procedure to rule out air locks
  6. If electrical checks pass but the pump does not respond, substitute a known-good pump or perform a resistance check on the pump motor
  7. After repair, clear codes and verify communication with the pump is restored and no new codes return during a road test

What a U01BC really tells you

  • A U01BC does not always mean the pump itself has failed; a low coolant level or air lock can cause the pump to overheat and shut down, setting a communication code without any electrical fault.
  • On many vehicles the charge air cooler pump only runs under boost or when intake air temperature exceeds a threshold, so a failed pump may not set the code until the engine is driven hard.
  • Technicians often replace the pump only to find the real fault is a corroded connector or a chafed wire behind the intercooler, so always inspect the harness before condemning the pump.
  • A weak or failing battery or charging system can cause multiple U-codes, including U01BC, because low voltage disrupts CAN communication; check system voltage before chasing the pump.
  • The code can be set by a fault in the pump's control module or its software, and a reflash or module replacement may be required even when the pump and wiring test good.

Can I keep driving with U01BC?

You can usually drive the vehicle short distances at light throttle to a repair shop, but avoid heavy acceleration, towing, or sustained high-load driving because a failed charge air cooler pump can cause intake air temperatures to spike and the ECM to derate power. If the engine enters limp mode or you notice a significant loss of power, stop and have the vehicle towed.

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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