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DTC codes / Subaru codes / P1500

P1500 · SubaruRadiator Fan Relay 1 Circuit Malfunction

P1500 on a Subaru indicates that the engine control module (ECM) has detected an abnormal condition in the electrical circuit for radiator fan relay 1, which controls the main cooling fan. The ECM monitors the relay's control circuit for expected voltage or current feedback and sets this code when the signal is outside the factory-specified range, often due to an open, short, or faulty relay.

SystemPowertrain
Code typeSubaru specific
SeverityMedium
Fix difficultyIntermediate
AreaVehicle speed, idle control and auxiliary inputs

Symptoms you may notice

  • Illumination of the check engine light or service engine soon light.
  • Often no symptoms besides the warning light, especially if the fan still operates via the second relay or at higher temperatures.
  • Engine coolant temperature may rise above normal in traffic or during extended idling if the fan fails to run.
  • The radiator fan may run continuously or not at all, depending on the nature of the circuit fault.
  • Possible overheating warning light or message on the dashboard in severe cases.
  • A slight burning smell or visible damage at the relay or connector in rare instances.

Common causes, most likely first

  1. Faulty radiator fan relay 1 (most common cause on older Subaru models).
  2. Corroded, loose, or damaged electrical connector at the relay or fan motor.
  3. Open or shorted wire in the relay control circuit between the ECM and the relay.
  4. Failed radiator fan motor drawing excessive current or causing a short.
  5. Blown fuse or fusible link supplying power to the relay circuit.
  6. Poor ground connection for the relay or fan motor.
  7. Rarely, a faulty ECM driver for the relay control circuit.

How to diagnose and fix it

  1. Verify the code with an OBD-II scanner and inspect the radiator fan relay 1 and its connector for corrosion or damage.
  2. Check the fuse and fusible link that supply power to the relay and fan circuit.
  3. Test the relay by swapping it with a known-good identical relay (e.g., fan relay 2) and clear the code to see if it returns.
  4. Measure resistance and voltage on the relay control circuit between the ECM and relay to check for opens or shorts.
  5. Test the radiator fan motor by applying 12 volts directly; replace if it fails to run or draws excessive current.
  6. Inspect and clean ground connections for the fan circuit, ensuring tight and corrosion-free contact.
  7. If all external components test good, diagnose the ECM control signal with an oscilloscope or bidirectional scan tool before condemning the ECM.

Relay Swap and Circuit Checks Before ECM Replacement

  • On many Subaru models, radiator fan relay 1 and relay 2 are identical; swapping them is a quick diagnostic step that can confirm a faulty relay without any tools.
  • A P1500 can be set by a fan motor that still spins but draws excessive current, which stresses the relay and eventually causes circuit feedback outside the expected range.
  • Corrosion inside the relay socket or fan connector is a frequent hidden cause, especially in regions with road salt, and may not be obvious without disconnecting and inspecting the terminals.
  • The ECM rarely fails; technicians who replace it based solely on P1500 often find the code returns because the underlying wiring or fan motor issue was missed.
  • This code does not always mean the fan is inoperative; it can set if the fan runs when commanded off or if the relay coil circuit has an intermittent short.

Can I keep driving with P1500?

You can usually drive short distances with P1500, but monitor the coolant temperature gauge closely and avoid prolonged idling or heavy traffic that relies on the radiator fan. If the temperature rises above normal or the overheating warning appears, stop safely and shut off the engine to prevent damage.

Tools that help

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

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