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DTC codes / GM codes / P1487

P1487 · GMHi Speed Rad Fan CTRL Relay Circuit Open Or Shorted

P1487 indicates that the powertrain control module (PCM) has detected an open or shorted circuit in the control side of the high-speed radiator fan relay. The PCM commands the relay on or off and monitors the circuit for expected voltage, so this code means the electrical path to the relay coil is broken or shorted to ground or power.

SystemPowertrain
Code typeGM specific
SeverityMedium
Fix difficultyIntermediate
AreaAuxiliary emission controls

Symptoms you may notice

  • The service engine soon light is illuminated on the instrument cluster.
  • The high-speed radiator fan may not run at all, even when the engine is hot or the air conditioning is on.
  • The engine coolant temperature may rise above normal in traffic or during extended idling.
  • The air conditioning may become less effective because the high-speed fan is needed to move air across the condenser.
  • Often no symptoms besides the warning light, especially if the low-speed fan circuit still functions.

Common causes, most likely first

  1. A failed high-speed radiator fan relay, typically due to an open coil or burned contacts inside the relay.
  2. A broken, corroded, or disconnected wire in the control circuit between the PCM and the relay.
  3. A short to ground or short to voltage in the relay control wire, often caused by chafing against a metal bracket.
  4. A faulty powertrain control module (PCM) driver circuit, though this is less common than wiring or relay issues.
  5. Corrosion or loose pins at the relay socket or at the PCM connector.
  6. Aftermarket alarm or remote start wiring that has tapped into the fan circuit and created an open or short.

How to diagnose and fix it

  1. Verify the code with a scan tool and check for any related fan or cooling system codes before proceeding.
  2. Inspect the high-speed fan relay and its socket for corrosion, loose pins, or a loose relay; swap the relay with a known-good identical relay to see if the code changes.
  3. Use a digital multimeter to check for battery voltage at the relay coil control terminal with the key on and the fan commanded on; if voltage is missing, trace the control wire back to the PCM.
  4. Check the control wire for continuity to ground and for short circuits to ground or power; repair any chafed or broken wires and secure the harness away from heat and moving parts.
  5. If the control wire is intact, test the PCM driver by commanding the fan on with a scan tool and watching for the ground pulse at the PCM connector; a missing pulse indicates a faulty PCM.
  6. Clear the code and verify the high-speed fan operates correctly when commanded, then road-test the vehicle to confirm the code does not return.

Don't overlook the relay socket and PCM driver

  • A common mistake is replacing the fan motor when the actual fault is an open relay coil or a corroded relay socket, so always test the control circuit before condemning the fan.
  • The high-speed fan relay is often identical to the low-speed fan relay, so swapping them is a quick diagnostic step that can confirm a failed relay without any tools.
  • A short in the control wire can be intermittent and may only set the code when the engine bay is hot or when the harness moves, so wiggle-test the harness while watching live data.
  • The PCM driver for the fan relay can be damaged by a shorted relay coil, so if a new relay fails immediately, check the coil resistance and the control wire for a short to power.
  • Aftermarket remote start or alarm systems that tap into the fan circuit are a frequent cause of unexplained open or short codes on older GM vehicles.

Can I keep driving with P1487?

You can usually drive the vehicle short distances if the temperature gauge stays in the normal range, but avoid heavy traffic, prolonged idling, and towing until the fault is repaired. If the coolant temperature rises above normal or the air conditioning stops cooling, pull over and let the engine cool to prevent overheating damage.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

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

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