OBD-II code · Network (extended)
U3573 Coolant Mixing Valve Control Circuit
Generic electrical fault on the coolant mixing valve control. The valve blends hot and cold coolant streams to maintain stack temperature.
Is it safe to drive with U3573?
Usually safe for short trips, but don’t ignore it: the underlying fault can get more expensive over time.
Common causes
- Most likelyValve actuator failed
- Less likelyGateway module routing CAN messages incorrectly
- Less likelyCAN terminating resistor (120 Ω) drifted out of spec
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
Repair at a glance
- Difficulty
- Hard
- DIY friendly
- Best left to a mechanic
- Typical labour
- 1–4 h
- Emissions test
- Usually unaffected
- After the fix
- A drive cycle is needed before the light stays off
- Parts involved
- Coolant Mixing Valve, Valve Wiring
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.