Fault in the stack inlet coolant temperature sensor (internal open or short, or drift); Damaged, chafed or corroded wiring to the sensor (open circuit, short to earth or short to supply); Poor connection at the sensor or control unit connector (corrosion, water ingress, loose terminal); Coolant level low or air in the stack coolant circuit giving false or erratic readings; Coolant pump, valve or flow fault making the reading disagree with other temperature sensors; Fault in the controlling module or its sensor reference supply or earth.

U3570

Stack Inlet Coolant Temperature Sensor 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
70: FaultThe specific fault in that area

What it means

U3570 is defined under the generic SAE J2012 scheme as a fault in the stack inlet coolant temperature sensor circuit. This points to a fuel cell vehicle, where the sensor measures coolant temperature entering the fuel cell stack. The control unit sets the code when the signal is out of range, implausible, missing, or disagrees with other temperature data. The exact trigger limits and monitoring strategy depend on the vehicle and manufacturer.

Symptoms

Warning light or system fault message on the dashboard
Reduced power or limited performance mode
Fuel cell system shutting down or refusing to start
Cooling fan or coolant pump running at an unusual speed
Other stored codes for coolant temperature or thermal management

Possible causes

Fault in the stack inlet coolant temperature sensor (internal open or short, or drift)likely
Damaged, chafed or corroded wiring to the sensor (open circuit, short to earth or short to supply)likely
Poor connection at the sensor or control unit connector (corrosion, water ingress, loose terminal)possible
Coolant level low or air in the stack coolant circuit giving false or erratic readingspossible
Coolant pump, valve or flow fault making the reading disagree with other temperature sensorspossible
Fault in the controlling module or its sensor reference supply or earthrare

How to diagnose

Read all stored and pending codes and note any related thermal management or voltage codes
Review freeze frame data and live coolant temperature values, and compare the stack inlet reading with other coolant temperature sensors and ambient temperature
Check coolant level and condition, and look for leaks, following the manufacturer's procedure for this system
Visually inspect the sensor, its wiring and connectors for damage, chafing, corrosion and water ingress
Wiggle-test the harness and connector with live data displayed to look for dropouts or jumps in the reading
Measure sensor resistance or signal voltage against the manufacturer's specification, and check the reference supply and earth at the connector
Check wiring continuity and insulation between the sensor and control unit with the system safely isolated
Check coolant pump and valve operation and flow, using the model-specific procedure

How to fix

Replace the stack inlet coolant temperature sensor if it is out of specification
Repair or replace damaged wiring and fix any short or open circuit
Clean, repair or replace corroded or loose connectors and terminals
Top up or refill the coolant and bleed air from the circuit using the specified procedure
Repair or replace a faulty coolant pump or valve that is causing implausible readings
Diagnose and repair or replace the control unit only after all other causes are ruled out, following the manufacturer's guidance

Can I keep driving?

Medium severity

The vehicle may be driven cautiously for a short time if it runs normally, but get it checked soon because the system cannot monitor stack temperature reliably. Stop driving if a overheating warning appears, power drops sharply or the system shuts down. The fuel cell and high-voltage systems should only be worked on by suitably trained technicians.

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