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Home / DTC / U0641 — Lost Communication With EVAP System Pressure Sensor/Switch Circuit A

U0641 — Lost Communication With EVAP System Pressure Sensor/Switch Circuit A

Detailed page for trouble code U0641.

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Code

U0641

Generic U — Network/User

Lost Communication With EVAP System Pressure Sensor/Switch Circuit A

Brand: Generic
Type: U — Network/User
Views: UK: 20 EN: 23 RU: 17
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Page language: EN

Causes

  • Open, shorted or damaged wiring between sensor and control module
  • Corroded, loose or contaminated connector at the EVAP pressure sensor
  • Failed EVAP pressure sensor or sensor switch
  • Loss of sensor reference power or ground (blown fuse, poor ground)
  • Intermittent connection (vibration, heat-related)
  • Faulty PCM/EVAP control module or internal module communications fault

Symptoms

  • Check Engine Light (MIL) illuminated
  • Stored U0641 with diagnostic trouble codes related to EVAP
  • EVAP system self-test not completed or not available
  • Possible trouble codes for related modules (loss of comm messages)
  • No obvious driveability symptoms in many cases

What to check

  • Read and record all DTCs and freeze-frame data with a scan tool; note related codes
  • Visually inspect EVAP pressure sensor, connector and wiring for corrosion, damage or water ingress
  • Check fuses and power supply circuits for the EVAP sensor/EVAP module
  • Backprobe sensor connector: verify reference voltage (often ~5 V) and ground presence
  • Measure sensor signal voltage while key ON and during engine run, compare to expected range
  • Wiggle harness and connectors while observing live data for intermittent faults

Signal parameters

  • Reference voltage: typically ~5.0 V (check vehicle-specific spec)
  • Signal output: typically 0.5–4.5 V proportional to measured EVAP pressure (varies with model)
  • Ground:
  • If sensor is a switch: open/closed continuity on switch circuit when actuated
  • Digital sensors: valid message on vehicle bus (CAN/LIN) containing EVAP pressure data

Diagnostic algorithm

  1. Retrieve and save all diagnostic codes and freeze-frame information. Note when U0641 first set.
  2. Inspect the EVAP pressure sensor harness and connector for damage, corrosion, loose pins or water.
  3. Verify power and ground at the sensor connector with key ON. If missing, trace/repair fuse, power feed or ground.
  4. Backprobe the signal wire and measure voltage while operating system or applying known pressure; compare to spec.
  5. Wiggle the harness and connectors while monitoring live data to locate intermittent faults.
  6. If the vehicle uses a networked sensor, check the vehicle bus (CAN/LIN) for activity and other module comms; scan for related U‑codes.
  7. Repair damaged wiring, clean/replace corroded connectors, and secure grounds. Re-test after each repair action.
  8. If wiring and supply checks are good and sensor signal is out of range or absent, replace the EVAP pressure sensor/switch.
  9. After repair or replacement, clear codes, perform readiness/EVAP tests and road test to confirm the issue does not return.
  10. If fault persists after sensor replacement and harness repair, consider module-level diagnostics or software update from manufacturer.

Likely causes

  • Damaged/loose connector at the EVAP pressure sensor
  • Broken or chafed wiring in harness to sensor
  • Failed sensor (most likely if wiring and power/ground are good)
  • Blown fuse or poor ground to EVAP control circuit
  • Intermittent wiring fault revealed under movement or temperature change
  • Module communication fault or rare ECU internal failure

Fault status

⚠️ Status
Lost communication with EVAP system pressure sensor/switch circuit A — no valid signal/data received from the sensor.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

U0100 U0121 U0140 P0455 P0442 P0456
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