U3574 code meaning
Coolant Mixing Valve
Network system Generic code U35xx codes Check engine light
What U3574 means
U3574 serves as the catch-all for the coolant mixing valve when the trouble lies in its behaviour rather than its wiring: it sticks, moves too slowly or misses the commanded split between radiator and bypass. Temperatures reveal it, because GM sets stack outlet temperature with this valve and the inlet-to-outlet difference with pump speed, so a jammed valve upsets both. Toyota plans for the case: before each start the valve runs to a fully open end position to reset its zero point, and in one variant it is left open toward the radiator at shutdown, so a valve that seizes later still cools the stack. Hyundai patented a lower-friction plunger seal for its stack coolant valve against leaks and wear. No maker documents U3574 publicly. Expect a warning, swinging temperatures and less power.
U3574 at a glance
- Check engine lightYes, usually on
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyHard
- Typical labor1 to 4 hours
- Clears after repairAfter a drive cycle
Symptoms of U3574
- Fuel cell system warning, MIL on
- Stack temperature swings or stays too high under load
- Reduced power, slow warm-up in cold weather
Common causes of U3574
- PossibleValve element sticking from deposits, worn seal or unsuitable coolant
- PossibleActuator gear or motor worn, valve moves sluggishly
- Less likelyInternal leak, coolant passes the closed port
- Less likelyAir in the stack coolant loop after service distorting the temperature response
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Coolant mixing valve
What each part of U3574 means
| U | Network system: communication between the control modules (CAN bus). |
| 3 | Reserved range, usually generic. |
| 74 | The exact fault in that area. |
What to do next
- Note U3574 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U3574
What does U3574 mean?
U3574 means "Coolant Mixing Valve". U3574 serves as the catch-all for the coolant mixing valve when the trouble lies in its behaviour rather than its wiring: it sticks, moves too slowly or misses the commanded split between radiator and bypass. It is a generic code, so it means the same on every make.
Is it safe to drive with U3574?
Drive gently and only to a workshop. With U3574 the car can go into limp mode (reduced power) to protect itself.
Will U3574 fail an emissions test?
U3574 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is U3574 to fix?
Difficulty: hard. A typical repair takes 1 to 4 hours of work. This is a job for a workshop.
Will U3574 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.