Faulty coolant mixing valve actuator or internal valve failure; Damaged or corroded wiring harness or connector at the valve; Open or short circuit in the control circuit between the PCM and the valve; Blown fuse or poor ground connection for the valve circuit; PCM software issue or internal driver failure (less common); Coolant contamination or debris causing the valve to seize; Aftermarket or incorrect valve replacement not compatible with the vehicle's system

DTC codes / U35xx · Network communication / U3573

U3573Coolant Mixing Valve Control Circuit

Q: What does code U3573 mean?

Coolant Mixing Valve Control Circuit. U3573 is a generic network code indicating that the powertrain control module (PCM) has detected a fault in the electrical circuit that controls the coolant mixing valve, which regulates coolant flow between the engine, heater core, and radiator. The PCM monitors the control circuit for expected voltage or current changes when commanding the valve, and it sets this code when the feedback does not match the command, indicating an open, short, or component failure.

U3573 is a generic network code indicating that the powertrain control module (PCM) has detected a fault in the electrical circuit that controls the coolant mixing valve, which regulates coolant flow between the engine, heater core, and radiator. The PCM monitors the control circuit for expected voltage or current changes when commanding the valve, and it sets this code when the feedback does not match the command, indicating an open, short, or component failure.

SystemNetwork

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaNetwork communication

Symptoms you may notice

Illumination of the malfunction indicator lamp (MIL) on the dashboard
Often no symptoms besides the warning light, especially if the valve fails in a default position
Incorrect cabin heater performance, such as blowing cold air when heat is requested
Engine temperature fluctuations or prolonged warm-up times
Reduced fuel economy or increased emissions due to improper coolant temperature management
Possible activation of related cooling system codes or powertrain network codes

Common causes, most likely first

Faulty coolant mixing valve actuator or internal valve failure
Damaged or corroded wiring harness or connector at the valve
Open or short circuit in the control circuit between the PCM and the valve
Blown fuse or poor ground connection for the valve circuit
PCM software issue or internal driver failure (less common)
Coolant contamination or debris causing the valve to seize
Aftermarket or incorrect valve replacement not compatible with the vehicle's system

How to diagnose and fix it

Perform a visual inspection of the coolant mixing valve, its connector, and wiring for damage, corrosion, or coolant leaks
Check the fuse and ground connections related to the valve circuit
Use a scan tool to command the valve and observe live data for actuator response and circuit feedback
Measure resistance and voltage at the valve connector to compare with manufacturer specifications
Test the control circuit for continuity and shorts between the PCM and the valve
If the circuit tests good, remove the valve and inspect for mechanical binding or debris; replace if faulty
After repair, clear the code and perform a road test to verify the fix and ensure the monitor runs to completion

Coolant Mixing Valve Circuit Pitfalls

A coolant mixing valve that fails in a default position may not cause noticeable drivability issues, leading owners to ignore the code until secondary problems arise.
Corrosion inside the valve connector is a frequent cause that can mimic a failed valve, so always inspect the pins before condemning the component.
The PCM may set U3573 even when the valve is functioning mechanically but the feedback signal is intermittent due to a chafed wire.
Some vehicles use the coolant mixing valve for both heater control and engine temperature management, so a fault can affect cabin comfort and emissions.
After replacing the valve, some systems require a relearn or calibration procedure with a scan tool to prevent the code from returning.

Can I keep driving with U3573?

You can usually continue driving with this code, but avoid long trips or heavy loads until it is repaired, and monitor the engine temperature gauge for overheating. If the engine overheats or you lose cabin heat entirely, stop driving and seek service.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.