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Home / DTC / U3571 — Stack Outlet Coolant Temperature Sensor 1 Circuit

U3571 — Stack Outlet Coolant Temperature Sensor 1 Circuit

Detailed page for trouble code U3571.

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Code

U3571

Generic U — Network/User

Stack Outlet Coolant Temperature Sensor 1 Circuit

Brand: Generic
Type: U — Network/User
Views: UK: 13 EN: 22 RU: 16
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Page language: EN

Causes

  • Open or shorted wiring in the sensor circuit
  • Corroded, loose, or contaminated connector at the sensor
  • Failed coolant temperature sensor (thermistor)
  • Poor or missing ground or reference voltage from control module
  • Coolant intrusion or corrosion at the sensor/connector
  • Control module (ECM/TCM) internal fault or incorrect software/calibration

Symptoms

  • Malfunction Indicator Lamp (MIL) or coolant warning lamp illuminated
  • Incorrect or erratic coolant temperature gauge or scan tool reading
  • Cooling fan operation may be incorrect (runs constantly or not at expected temps)
  • Heater or HVAC performance poor (insufficient cabin heat)
  • Possible reduced engine performance or warm-up related drivability issues
  • Stored freeze frame / trouble code pointing to stack outlet sensor circuit

What to check

  • Scan for U3571 and any related frozen data; note occurrence conditions (engine temp, load, ambient)
  • Check live coolant temperature PID on scan tool and compare to ambient and expected rise after start
  • Visually inspect sensor connector and wiring for corrosion, damage, or coolant contamination
  • With engine cold and ignition ON, backprobe connector to confirm reference voltage (typically ~5V) and ground presence
  • Measure sensor resistance vs temperature (remove sensor if necessary) and compare to specification or typical thermistor behavior
  • Perform continuity and short tests between sensor pin and control module pin (check for short to battery or ground)

Signal parameters

  • Typical type: NTC thermistor (resistance decreases as temperature increases)
  • Common electrical behaviour (generic): cold (~-40°C) = very high resistance (tens to hundreds of kilo-ohms); ambient (~20°C) = ~1–10 kΩ; hot (~80–100°C) = a few hundred to a thousand ohms (vehicle-specific)
  • Typical voltage signal (when used with ECU pull-up to 5V): cold → high voltage (~4.0–4.5 V), hot → low voltage (~0.3–1.0 V). Exact values depend on sensor design and ECU wiring
  • Reference circuit normally uses a stable 5V supply and a dedicated ground — verify both are within specifications

Diagnostic algorithm

  1. Retrieve freeze frame data and confirm U3571 is current or historic; note engine temp, runtime, and conditions
  2. Confirm symptom with live data: compare ECT (stack outlet) reading to other coolant temperature sensors (if present) and ambient temperature
  3. Perform visual inspection of sensor, harness, and connector for damage or contamination; dry and clean connector if needed
  4. With ignition ON (engine OFF), backprobe the connector: verify reference voltage (approx. 5V), verify ground continuity to chassis/ECM, and check for voltage present at the signal pin
  5. Measure resistance of the sensor at ambient temperature (engine cold) and, if safe, heat the sensor in controlled way (hot water) to confirm resistance changes smoothly with temperature—compare to specification or expected thermistor curve
  6. Check continuity from sensor signal pin to the ECU connector; check for shorts to power or ground
  7. If wiring and connector are good, replace the sensor and retest; use OEM-equivalent sensor and torque to spec, then refill/bleed cooling system if removed
  8. Clear codes and perform a test drive / warm-up cycle while monitoring live data to confirm fault does not return
  9. If fault returns after sensor and harness repair, consider ECU input circuit testing or replacement — consult manufacturer guidance before replacing module

Likely causes

  • Damaged harness (chafing, pinched, rodent chew) between sensor and module
  • Corroded connector pins or water intrusion at sensor connector
  • Failed sensor element due to coolant contamination or age
  • Poor ground or blown fuse for sensor reference/ground
  • Intermittent wiring/connector contact causing sporadic signal

Fault status

⚠️ Status
Stack Outlet Coolant Temperature Sensor 1 circuit malfunction detected — open, short, intermittent, or implausible signal.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

P0115 P0116 P0117 P0118 P0125 P0128
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