Failed high-speed radiator fan relay, often due to burned contacts or a cracked solder joint inside the relay; Open or corroded wiring between the ECM and the relay control coil, commonly at connector terminals in the underhood fuse box; Shorted relay control wire to ground or to power, often from chafing against a bracket or heat damage near the exhaust; Faulty radiator fan motor drawing excessive current or seized, which can stress the relay circuit; Poor ground connection at the relay mounting point or fan motor ground strap; ECM driver circuit failure, rare but possible after a shorted relay coil or water intrusion into the ECM connectors

DTC codes / Mitsubishi codes / P1487

P1487 · MitsubishiHigh Speed Radiator Fan Control Relay Circuit Fault

Q: What does code P1487 mean?

High Speed Radiator Fan Control Relay Circuit Fault. P1487 on Mitsubishi vehicles means the engine control module (ECM) has detected an electrical fault in the high-speed radiator fan control relay circuit, which is the circuit that commands the fan to run at full speed when coolant temperature rises or the air conditioning (A/C) is on. The ECM monitors the relay control wire for expected voltage changes and sets this code when the signal does not match what the commanded fan state should produce.

P1487 on Mitsubishi vehicles means the engine control module (ECM) has detected an electrical fault in the high-speed radiator fan control relay circuit, which is the circuit that commands the fan to run at full speed when coolant temperature rises or the air conditioning (A/C) is on. The ECM monitors the relay control wire for expected voltage changes and sets this code when the signal does not match what the commanded fan state should produce.

SystemPowertrain

Code typeMitsubishi specific

SeverityMedium

Fix difficultyIntermediate

AreaAuxiliary emission controls

Symptoms you may notice

Often no symptoms besides the warning light, especially in cool weather or short trips
Radiator fan does not run at high speed, leading to coolant temperature rising in traffic or when the A/C is on
A/C cooling performance drops or the A/C compressor cuts out when the fan fails to engage
Coolant temperature gauge climbs above normal during extended idling or hot-day driving
Fan may run continuously at high speed if the relay control circuit is shorted to ground
Possible engine overheating and coolant boil-over in severe cases

Common causes, most likely first

Failed high-speed radiator fan relay, often due to burned contacts or a cracked solder joint inside the relay
Open or corroded wiring between the ECM and the relay control coil, commonly at connector terminals in the underhood fuse box
Shorted relay control wire to ground or to power, often from chafing against a bracket or heat damage near the exhaust
Faulty radiator fan motor drawing excessive current or seized, which can stress the relay circuit
Poor ground connection at the relay mounting point or fan motor ground strap
ECM driver circuit failure, rare but possible after a shorted relay coil or water intrusion into the ECM connectors

How to diagnose and fix it

Verify the code with a scan tool and command the high-speed fan on and off while watching for relay click and fan operation
Inspect the underhood fuse box for the high-speed fan relay, check the fuse and swap the relay with an identical known-good relay to see if the fault follows
Measure resistance and voltage drop on the relay control wire from the ECM to the relay, looking for opens, shorts, or high resistance at connectors
Test the radiator fan motor directly with fused jumper wires to confirm it spins freely and does not draw excessive current
Check and clean the relay ground and fan motor ground connections, then retest the circuit
If the relay, wiring, and fan motor all test good, back-probe the ECM control wire to confirm the ECM is commanding the relay correctly before condemning the ECM
Clear the code and road-test with the A/C on and engine at operating temperature to confirm the high-speed fan engages and the code does not return

Why the high-speed fan relay code misleads

A fan motor that is beginning to seize can pass a quick spin test but draw enough current to damage the relay contacts over time, so always check motor current draw rather than just free rotation.
The high-speed fan relay is often shared with or controlled by the A/C system on Mitsubishi models, so an A/C pressure switch or A/C request fault can command the fan in a way that sets this code even when the fan circuit itself is sound.
Corrosion inside the underhood fuse box terminals is a common cause on older Mitsubishi vehicles, and the relay can test good on the bench while the socket terminals fail under load.
Some Mitsubishi ECMs set P1487 when the relay coil is open but the fan still runs on low speed through a separate circuit, so the driver may never notice a cooling problem until the engine is worked hard.
Replacing the relay without checking the fan motor and wiring often leads to a repeat failure, because a shorted or high-current fan motor will burn out the new relay contacts.

Can I keep driving with P1487?

You can drive short distances with the warning light on if the temperature gauge stays normal, but avoid heavy traffic, long idles, and towing until the high-speed fan is repaired. If the temperature gauge climbs above normal or the A/C stops cooling, pull over and shut the engine off to prevent overheating damage.

Tools that help

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