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DTC codes / P21xx · Fuel and air metering / P2185

P2185Engine Coolant Temperature Sensor 2 Circuit High

P2185 means the powertrain control module (PCM) has detected an abnormally high voltage on the signal circuit of engine coolant temperature sensor 2, which is typically the radiator outlet sensor on vehicles that use two coolant sensors. A high voltage reading on this circuit tells the PCM that the sensor is reporting an unrealistically cold temperature or that the circuit is open.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaFuel and air metering

Symptoms you may notice

  • Illuminated check engine light, often with no other noticeable symptoms
  • Cooling fan may run continuously or not at all because the PCM cannot trust the outlet temperature reading
  • Temperature gauge or coolant temperature display may behave erratically or read colder than normal
  • Poor fuel economy or slightly rough running if the PCM substitutes a default coolant temperature
  • Possible reduced engine power or cooling system warning message on some vehicles
  • Overheating risk if the fan control strategy is affected and the driver ignores the warning

Common causes, most likely first

  1. Open or damaged signal wire between sensor 2 and the PCM, often from corrosion or a broken conductor
  2. Failed engine coolant temperature sensor 2, typically an open thermistor element
  3. Poor electrical connection at the sensor 2 harness connector, including backed-out or corroded terminals
  4. High resistance in the sensor ground circuit shared with other sensors
  5. PCM internal fault on the sensor 2 input circuit, which is rare but possible
  6. Aftermarket sensor installed with incorrect resistance characteristics for the application

How to diagnose and fix it

  1. Scan all modules and record freeze-frame data for P2185 to confirm the fault occurred under specific coolant temperatures
  2. Inspect the sensor 2 connector and harness for corrosion, chafing, or a loose terminal, and repair as needed
  3. Measure sensor 2 resistance with a multimeter and compare it to the manufacturer's temperature-resistance chart
  4. Backprobe the sensor 2 signal circuit at the PCM and check voltage with the key on, engine off, looking for a value near 5 volts that does not change when the sensor is unplugged
  5. Check the sensor ground circuit for excessive resistance using a voltage drop test under load
  6. If the wiring and ground test good, substitute a known-good sensor and clear the code to see if it returns
  7. If the code persists with a known-good sensor and verified wiring, diagnose the PCM input circuit or replace the PCM as a last resort

Sensor 2 is not always the gauge sensor

  • Many vehicles use sensor 2 as the radiator outlet temperature sensor, so a P2185 can set even when the dashboard temperature gauge reads normally from sensor 1.
  • A common misdiagnosis is replacing sensor 1 because the code mentions coolant temperature, but P2185 specifically refers to the second sensor circuit.
  • The PCM may command the cooling fan on high as a fail-safe when sensor 2 voltage is high, which can drain the battery on vehicles that keep the fan running after shutdown.
  • Corrosion inside the sensor 2 connector is a frequent cause on vehicles driven in road-salt regions, and the terminals can look clean until the connector is opened.
  • A high voltage reading can also be caused by a poor ground shared with other sensors, so testing the ground circuit is as important as testing the signal wire.

Can I keep driving with P2185?

The vehicle is usually safe to drive short distances to a repair shop, but avoid heavy loads, long trips, or stop-and-go traffic where cooling fan operation is critical. If the temperature gauge climbs above normal or a cooling system warning appears, stop driving and let the engine cool.

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.

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