Network, generic (extended)

U3573 Coolant Mixing Valve Control Circuit

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

U3573 concerns how the coolant mixing valve is powered: its actuator line may be interrupted or shorted, or the output stage may have failed. This three-way valve splits stack coolant between radiator and bypass and so decides how warm it is when it returns to the stack. Designs vary: in a Hyundai application a solenoid pushes a spool and its current sets the split, while Toyota describes a rotary valve turned by a stepper motor through a gear train. In the conventional Hyundai layout the valve takes the stack inlet temperature over CAN from the fuel cell control unit. If the actuator cannot be powered, coolant temperature is no longer regulated. U3573 appears in no public maker document. Likely consequences are a warning and capped output; how the valve itself responds is judged under U3574.

Likely causes

Open, short or corrosion in wiring or connector of the valve actuator
Actuator motor or solenoid coil of the mixing valve faulty
Driver stage or CAN link of the controlling unit faulty

Symptoms

  • Fuel cell system warning, MIL on
  • Stack temperature too high or too low, reduced power
  • Slow warm-up of the fuel cell system

Repair estimate

DifficultyHardWorkshop job
Parts and labour€200–1,200
Time1–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

coolant mixing valvevalve wiring

Related codes

U3574U3575U3570

References: patents.google.com, patents.google.com, patents.google.com.