U3571: Stack Outlet Coolant Temperature Sensor 1 Circuit

What it means

Generic fault on coolant temperature sensor 1 at the fuel cell stack outlet (used to monitor stack thermal output).

At a glance

• Usually lights the warning light of the system that lost communication

How it works

Stack outlet coolant temperature sensor 1 measures coolant temperature as it leaves the fuel cell stack, helping the control system monitor heat coming from the stack. This code points to a fault associated with sensor 1's circuit or reported data, though CAN message routing or network termination can produce related communication faults.

Common causes

Most likely first.

1. Sensor failed
2. Gateway module routing CAN messages incorrectly
3. CAN 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

How to diagnose it

1. Record freeze-frame data and scan all modules for related communication codes to establish whether the issue concerns outlet sensor 1 or a wider CAN problem.
2. Compare sensor 1's reported outlet temperature with the inlet reading and other available coolant temperatures for an implausible or missing value.
3. Inspect the sensor 1 connector and wiring at the stack outlet for looseness, corrosion, chafing, or damage.
4. Test sensor 1 and its circuit using the vehicle's service information and the manufacturer's specification.
5. If multiple modules report communication faults, check gateway routing and CAN wiring and termination against the manufacturer's specification.

Common fixes

• Reconnect or repair a loose or damaged sensor 1 connector or harness.
• Replace a faulty stack outlet coolant temperature sensor 1.
• Correct a gateway routing fault affecting the sensor data.
• Repair CAN wiring or replace an out-of-spec terminating resistor.

Can I keep driving?

Avoid demanding operation if warnings or reduced power appear, because the system may not reliably monitor stack outlet temperature. Stop if the fuel cell system shuts down or the vehicle displays a stop warning.