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DTC codes / Chrysler codes / P1199

P1199 · ChryslerRadiator Temperature Sensor Voltage Too Low

P1199 on Chrysler vehicles means the powertrain control module (PCM) has detected a voltage signal from the radiator temperature sensor that is lower than the expected range, typically below 0.2 volts. The sensor is a thermistor that changes resistance with temperature, and a low voltage indicates either an abnormally hot reading, a short to ground in the signal circuit, or a sensor that has failed. The PCM sets this code when the signal stays out of range for a calibrated time, often triggering the cooling fan strategy to default to a safe mode.

SystemPowertrain
Code typeChrysler specific
SeverityMedium
Fix difficultyIntermediate
AreaFuel and air metering

Symptoms you may notice

  • Illumination of the check engine light, often with no other noticeable symptoms
  • Cooling fan may run continuously or at high speed because the PCM defaults to a safe strategy
  • Temperature gauge may read abnormally high or fluctuate if the sensor signal is skewed
  • Poor fuel economy or slightly rough running if the PCM enriches the mixture based on a false hot reading
  • In rare cases, the engine may enter a reduced power mode or set companion codes for fan control

Common causes, most likely first

  1. Radiator temperature sensor internally shorted, pulling the signal voltage to ground
  2. Chafed or pinched signal wire shorting to ground between the sensor and the PCM
  3. Corroded or water-intruded connector at the radiator temperature sensor
  4. Faulty PCM driver or internal ground reference issue (less common)
  5. Aftermarket sensor with incorrect resistance curve installed during prior repairs
  6. Coolant contamination or sensor tip coated with debris causing a false low-resistance reading

How to diagnose and fix it

  1. Scan all modules and record freeze-frame data to confirm the code is active and not a historical glitch
  2. Visually inspect the radiator temperature sensor connector and harness for corrosion, chafing, or coolant intrusion
  3. Measure sensor resistance with a multimeter and compare to the Chrysler specification for the ambient temperature
  4. Backprobe the signal wire at the sensor and check voltage with the key on; a reading near 0 volts suggests a short to ground
  5. Disconnect the sensor and recheck the signal voltage at the harness; if it rises to about 5 volts, the sensor is shorted
  6. If the harness voltage stays low with the sensor disconnected, trace the signal wire for a short to ground or repair the PCM connector
  7. Replace the radiator temperature sensor only after electrical checks confirm it is the fault, then clear codes and verify the fan strategy returns to normal

Radiator sensor shorts that fool fan diagnostics

  • A shorted radiator temperature sensor often causes the cooling fan to run constantly, which masks the real problem and leads to unnecessary fan motor or relay replacement.
  • The radiator temperature sensor is separate from the engine coolant temperature sensor on many Chrysler models, so a normal dash gauge does not rule out a faulty radiator sensor.
  • Water intrusion into the sensor connector from pressure washing or road splash is a frequent cause of a low-voltage signal that intermittently sets P1199.
  • Technicians sometimes replace the PCM when the actual fault is a chafed signal wire behind the radiator shroud, so always perform a loaded voltage drop test on the ground circuit.
  • P1199 can be set by a sensor that reads correctly at room temperature but breaks down when hot, so testing cold and after a road test is essential.

Can I keep driving with P1199?

You can usually drive the vehicle short distances to a repair shop, but avoid heavy loads, trailer towing, or sustained high-speed driving because the cooling fan may not operate correctly and the engine could overheat. If the temperature gauge climbs above normal or the fan runs continuously, stop and have the fault diagnosed before continuing.

Tools that help

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

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