U3573

Code

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

Confirm the code and record freeze-frame and related codes. Clear codes and attempt to re-create condition by commanding valve or driving vehicle.
Visually inspect mixing valve, harness and connector for damage, contamination or coolant intrusion; repair or replace as needed.
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).
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.
Measure actuator resistance with connector disconnected and compare to spec. If open or out-of-range, replace valve.
Wiggle test wiring and connectors while monitoring live data or voltages to find intermittent faults.
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.
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

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