Damaged, corroded or loose connector at the stack outlet coolant temperature sensor; Open circuit, short to earth or short to supply in the sensor wiring; Faulty stack outlet coolant temperature sensor; Low coolant level or air in the stack cooling circuit giving implausible readings; Fault in the fuel cell control unit or the module reading the sensor; Outdated or faulty control unit software where the manufacturer has issued a fix for this code.

U3571

Stack Outlet Coolant Temperature Sensor 1 Circuit.

Generic
Network
Generic code
Medium severity

How this code is built

U: SystemNetwork
3: Defined bySAE, the same on every car
5: AreaNetwork area 5
71: FaultThe specific fault in that area

What it means

U3571 is the generic code for a fault in the Stack Outlet Coolant Temperature Sensor 1 circuit. This sensor is used on fuel cell vehicles to monitor the temperature of coolant leaving the fuel cell stack. The control unit sets the code when the signal is missing, implausible or outside its expected range, or when the data is not being received correctly. Exact wording, thresholds and which module sets it vary by model, so check the manufacturer's data.

Symptoms

Fuel cell or powertrain warning light on
Reduced power or limp mode
Cooling fan or coolant pump running harder than normal
Vehicle refusing to start or shutting down the fuel cell system
Temperature readings that are fixed, erratic or implausible on a scan tool

Possible causes

Damaged, corroded or loose connector at the stack outlet coolant temperature sensorlikely
Open circuit, short to earth or short to supply in the sensor wiringlikely
Faulty stack outlet coolant temperature sensorlikely
Low coolant level or air in the stack cooling circuit giving implausible readingspossible
Fault in the fuel cell control unit or the module reading the sensorrare
Outdated or faulty control unit software where the manufacturer has issued a fix for this coderare

How to diagnose

Read all stored and pending codes with freeze frame data, and note any other coolant, stack or communication codes.
Check the manufacturer's service information for this model, as fuel cell systems vary and need trained staff and the correct safety procedures.
Visually inspect the sensor, its connector and wiring for damage, chafing, coolant contamination and corrosion.
Check coolant level and condition, and look for leaks or signs of air in the stack cooling circuit.
Compare live stack outlet coolant temperature with other coolant temperature readings on a cold system; they should be similar.
Test the sensor circuit for supply, signal, earth and continuity, and measure the sensor's resistance against specification.
Check for relevant technical bulletins or software updates for this model.
Clear the code after repair and road test to confirm it does not return.

How to fix

Repair or replace damaged wiring, and clean or replace corroded or loose connectors.
Replace the stack outlet coolant temperature sensor if it is out of specification.
Correct the coolant level, then bleed the cooling circuit using the manufacturer's procedure.
Repair any coolant leaks found.
Update or reprogram the control unit software only if the manufacturer lists it as a fix for this fault.
Diagnose and repair or replace the control unit if the sensor and wiring test good.

Can I keep driving?

Medium severity

Short, careful journeys may be possible, but the stack temperature may not be monitored properly and the car may limit power or shut down. Stop and seek help if you see an overheating warning, coolant loss or a loss of power.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.