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Home / DTC / U066D — Lost Communication With Charge Air Cooler Temperature Sensor Bank 1

U066D — Lost Communication With Charge Air Cooler Temperature Sensor Bank 1

Detailed page for trouble code U066D.

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Code

U066D

Generic U — Network/User

Lost Communication With Charge Air Cooler Temperature Sensor Bank 1

Brand: Generic
Type: U — Network/User
Views: UK: 19 EN: 29 RU: 16
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Page language: EN

Causes

  • Open, shorted, or damaged sensor wiring or connector
  • Corroded, loose or contaminated connector terminals
  • Failed charge air cooler temperature sensor (thermistor/module)
  • Faulty power supply or ground for the sensor circuit
  • Faulty engine control module (ECM) or local sensor module
  • Intermittent connection due to vibration or harness chafing

Symptoms

  • Malfunction Indicator Lamp (MIL) or warning lamp illuminated
  • Stored U066D and possibly related communication or sensor fault codes
  • Reduced engine performance or turbo boost control anomalies
  • Poor fuel economy or rough running under load
  • Loss of boost and possible limp-home mode on some vehicles
  • No valid CACT reading visible on scan tool for Bank 1

What to check

  • Read and record freeze-frame and all related DTCs with a scan tool; note whether code is current or intermittent
  • Visually inspect CACT sensor connector and wiring on Bank 1 for corrosion, damage, pin push-out, or water ingress
  • Check for continuity and shorts to ground or battery on the sensor signal, power and ground circuits
  • Verify sensor supply/reference voltage and ground at the connector using a DVOM or oscilloscope
  • Monitor sensor signal with scan tool or oscilloscope while changing temperature (heat/cool) to verify response
  • Check CAN/LIN bus health (voltage levels, termination resistors, other modules present) if sensor communicates over network

Signal parameters

  • Sensor type: typically a thermistor (resistive) or temperature sensor producing a 0–5 V signal; specifics vary by vehicle
  • Expected sensor signal range: approximately 0.5–4.5 V depending on air temperature (varies by manufacturer)
  • Thermistor resistance varies with temperature—resistance decreases or increases with temperature depending on type (consult vehicle service data)
  • Reference power: usually 5 V supply or battery reference from the ECU and a solid ground—verify presence at connector
  • Communication bus (if used): CAN differential voltages ~2.5 V idle per side (CAN_H/CAN_L), LIN single-wire levels per manufacturer

Diagnostic algorithm

  1. Connect a capable scan tool, confirm U066D and read related codes and freeze-frame data. Note whether code is current or historic.
  2. Visually inspect the Bank 1 CACT sensor, connector, and harness for damage, corrosion, loose pins, or contaminated contacts. Repair obvious damage.
  3. Backprobe the sensor connector. With ignition on, verify correct reference voltage/pull-up and ground presence. Report any missing supply or open ground.
  4. Measure the sensor signal (voltage or resistance per vehicle spec) and observe while altering intake charge temperature (blow warm air or apply cold) to confirm the signal changes.
  5. If signal is absent or intermittent, check continuity between the sensor and the ECM connector for open/shorts and measure for resistance to ground/battery where appropriate.
  6. If the sensor communicates over a network, verify CAN/LIN bus integrity: check bus voltages, termination resistors, and presence of other modules. Use an oscilloscope if available.
  7. If wiring and bus are good, replace the CACT sensor with a known-good unit and retest. If swapping cures the fault, install new sensor and clear codes.
  8. If replacement sensor does not restore communication, trace and repair wiring to the ECM or test/replace the ECM or intermediate module as per manufacturer procedures.
  9. After repair, clear codes, perform functional tests and a road test to confirm the fault does not return.

Likely causes

  • Poor connector contact or corrosion at the CACT sensor
  • Broken or shorted harness between sensor and engine controller
  • Failed CACT sensor (open circuit or internal failure)
  • Loss of sensor reference voltage or ground at the sensor
  • Intermittent CAN/LIN communication fault or missing termination

Fault status

⚠️ Status
Lost communication with Charge Air Cooler Temperature Sensor Bank 1 — sensor signal missing or not received by control module.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

U0100 U0121 P0113 P0112 P0118
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