U3570: Stack Inlet Coolant Temperature Sensor Circuit

What it means

Generic fault on the coolant temperature sensor at the fuel cell stack inlet (deionized coolant cools the membrane electrode assemblies).

At a glance

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

How it works

The fuel cell stack inlet coolant temperature sensor reports the temperature of deionized coolant entering the stack to the control system. This code indicates a fault associated with that sensor circuit or its reported data, which may also result from CAN message routing or network termination problems.

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 see whether the fault is limited to the inlet temperature reading or affects the network.
2. Compare the reported stack inlet coolant temperature with other coolant readings and ambient conditions when the system is cold, looking for an implausible or missing value.
3. Inspect the inlet sensor connector and harness for loose connections, corrosion, damage, or signs of coolant intrusion.
4. Check the sensor circuit and sensor operation using the vehicle's service information and the manufacturer's specification.
5. If several modules show communication faults, check gateway configuration and CAN wiring and termination against the manufacturer's specification.

Common fixes

• Reconnect or repair a loose or damaged inlet sensor connector or harness.
• Replace a faulty stack inlet coolant temperature sensor.
• Correct gateway CAN message routing if configuration or operation is faulty.
• Repair CAN network wiring or replace an out-of-spec terminating resistor.

Can I keep driving?

If the vehicle shows multiple warnings, reduced power, or a fuel cell system shutdown, stop driving and follow the vehicle's safe shutdown guidance. An unreliable inlet temperature signal can prevent proper stack thermal monitoring.