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Home / DTC / U3573 — Coolant Mixing Valve Control Circuit

U3573 — Coolant Mixing Valve Control Circuit

Detailed page for trouble code U3573.

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U3573

Generic U — Network/User

Coolant Mixing Valve Control Circuit

Brand: Generic
Type: U — Network/User
Views: UK: 16 EN: 20 RU: 16
AI status
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Page language: EN

Causes

  • Open or shorted wiring in mixing valve circuit
  • Poor or corroded connector or terminal at valve or ECU/PCM
  • Bad ground or power supply to the valve
  • Faulty coolant mixing valve (actuator motor or internal electronics)
  • Failed driver circuit inside ECU/PCM or module communication fault
  • Contamination or coolant intrusion in valve/connector

Symptoms

  • Cooling system temperature imbalance between heater and engine loop
  • Poor cabin heating or sudden fluctuations in interior heat
  • Check Engine Lamp or ABS/other module warning illuminated if communications affected
  • Stored U3573 code and possibly related coolant/temperature codes
  • Clicking or no movement from valve when commanded
  • Intermittent symptoms that change with engine vibration or temperature

What to check

  • Read and record all stored DTCs and freeze-frame data with a capable scan tool
  • Check for related coolant temperature, HVAC blend door, fan and thermostat codes
  • Perform a visual inspection of the mixing valve, harness and connectors for corrosion, pin damage, coolant residue or burns
  • Verify battery voltage and engine ground quality before testing
  • Attempt an active test/command of the mixing valve with a scan tool and observe response
  • Backprobe connector to measure supply voltage, ground continuity and control signal while commanding

Signal parameters

  • Supply voltage: ~12 V nominal at idle/battery (should be within ~11–14 V)
  • Control signal: PWM or variable voltage from ECU (typical PWM frequencies 20–200 Hz — manufacturer-specific)
  • Control current: small actuator motors or solenoids typically 0.1–3 A depending on design
  • Idle (valve de-energized) resistance: commonly 5–50 ohms for coil/actuator (manufacturer-specific)
  • Position/feedback sensor (if present): 0–5 V analog or discrete position counts over CAN — check live data for expected range

Diagnostic algorithm

  1. Confirm the code and record freeze-frame and related codes. Clear codes and attempt to re-create condition by commanding valve or driving vehicle.
  2. Visually inspect mixing valve, harness and connector for damage, contamination or coolant intrusion; repair or replace as needed.
  3. With ignition ON (engine off), backprobe valve connector: verify battery voltage on power pin, verify good ground on ground pin. If no power or ground, trace and repair supply/ground (fuses, relays, grounds).
  4. Command the mixing valve using a scan tool while monitoring connector signals: observe control signal (voltage/PWM) and whether the valve moves. If commanded signal present but valve doesn't move, suspect valve failure. If commanded signal absent, suspect ECU/driver or wiring fault.
  5. Measure actuator resistance with connector disconnected and compare to spec. If open or out-of-range, replace valve.
  6. Wiggle test wiring and connectors while monitoring live data or voltages to find intermittent faults.
  7. If wiring and valve check good, check module outputs: measure signal at ECU connector while commanding. If the ECU output is missing or shorted to ground/power, consider ECU/module fault or short in harness. Avoid replacing ECU without confirming an external short isn't present.
  8. Repair or replace faulty connector/pins, wiring, relay, fuse, or mixing valve as indicated. After repair, clear codes and verify proper operation on road and with scan tool. If symptoms persist, consider professional module diagnostics.

Likely causes

  • Corroded connector at mixing valve or ECU
  • Open/shorted control wire or broken ground
  • Failed mixing valve motor or internal position sensor
  • ECU driver transistor or relay failure
  • Water/coolant ingress into connector causing short or corrosion

Fault status

⚠️ Status
Control circuit fault detected for the coolant mixing valve — the control module is not receiving expected signal/feedback or the valve is not responding. Possible wiring, connector, actuator or module fault.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

P0596 P0597 P0598 P0117 P0118 P0480
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