Faulty stack inlet coolant temperature sensor (internal failure or drift); Damaged or corroded wiring harness or connector at the sensor; Open circuit in the signal or ground circuit (broken wire, loose pin); Short to ground or short to voltage in the sensor circuit; Coolant level low or air pockets causing the sensor to read incorrectly; Contaminated or degraded coolant affecting sensor accuracy; PCM internal fault (rare, but possible after other causes are ruled out)

DTC codes / U35xx · Network communication / U3570

U3570Stack Inlet Coolant Temperature Sensor Circuit

Q: What does code U3570 mean?

Stack Inlet Coolant Temperature Sensor Circuit. U3570 indicates that the powertrain control module (PCM) has detected an abnormal signal from the stack inlet coolant temperature sensor circuit, which monitors the temperature of coolant entering the stack (exhaust stack or cooling stack) on vehicles equipped with such a sensor. The PCM sets this code when the sensor voltage falls outside the expected range for the current operating conditions, indicating an open, short, or out-of-range signal.

U3570 indicates that the powertrain control module (PCM) has detected an abnormal signal from the stack inlet coolant temperature sensor circuit, which monitors the temperature of coolant entering the stack (exhaust stack or cooling stack) on vehicles equipped with such a sensor. The PCM sets this code when the sensor voltage falls outside the expected range for the current operating conditions, indicating an open, short, or out-of-range signal.

SystemNetwork

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaNetwork communication

Symptoms you may notice

Illumination of the malfunction indicator lamp (MIL) on the dashboard
Often no symptoms besides the warning light, especially if the sensor is only slightly out of range
Reduced engine performance or power derate if the PCM enters a protection strategy
Poor fuel economy or increased regeneration frequency in vehicles with exhaust aftertreatment
In rare cases, overheating or abnormal temperature gauge readings if the sensor is used for cooling fan control
Possible limp mode or limited engine speed if the fault is severe and affects emissions or protection systems

Common causes, most likely first

Faulty stack inlet coolant temperature sensor (internal failure or drift)
Damaged or corroded wiring harness or connector at the sensor
Open circuit in the signal or ground circuit (broken wire, loose pin)
Short to ground or short to voltage in the sensor circuit
Coolant level low or air pockets causing the sensor to read incorrectly
Contaminated or degraded coolant affecting sensor accuracy
PCM internal fault (rare, but possible after other causes are ruled out)

How to diagnose and fix it

Verify the code with a scan tool and check for any related codes in other modules
Inspect the sensor connector and wiring for corrosion, damage, or loose pins
Measure the sensor resistance and compare to the manufacturer's temperature-resistance chart
Check the signal voltage at the PCM connector while wiggling the harness to detect intermittent faults
Test the sensor circuit for opens and shorts using a multimeter and wiring diagram
Replace the stack inlet coolant temperature sensor if resistance is out of specification
Clear the code and perform a road test to confirm the repair, then verify no pending codes return

What Most Techs Miss on U3570

A common mistake is replacing the sensor without checking the coolant level and condition; low coolant or air pockets can cause the sensor to read erratically and set this code.
The stack inlet coolant temperature sensor is often confused with the engine coolant temperature sensor, but they serve different systems; testing the wrong sensor wastes time and parts.
Intermittent wiring faults can set U3570 without leaving a permanent failure; always perform a wiggle test on the harness while monitoring sensor data.
On some vehicles, this code may be set by a faulty thermostat or water pump causing abnormal temperature fluctuations, so check the cooling system before condemning the sensor.
A poor ground connection at the sensor or PCM can skew the signal voltage; verify ground integrity with a voltage drop test rather than just continuity.

Can I keep driving with U3570?

You can usually drive with U3570 if the engine temperature gauge reads normally and there are no performance symptoms, but avoid heavy loads or long trips until diagnosed. If the engine overheats or enters limp mode, stop driving and seek service immediately to prevent damage.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.