P1490

P1490 on Honda is a Cooling Fan Relay Low Circuit fault, set when the PCM commands the radiator fan relay coil to energize (pulling its control pin to ground through a low-side driver) and does not see the expected voltage swing on the feedback line. The relay sits in the under-hood fuse/relay box and the fan motor itself draws 8 to 15 amps in steady state. Cheapest ladder: with the engine cool, command the fan on via HDS scan tool or jumper the A/C request to confirm the fan should run, then pull the cooling fan relay and bench-test it (apply 12V to the coil pins; the contacts should click and read continuity under 0.2 ohms). Swap it with an identical relay elsewhere in the same box (horn or fuel pump relay typically interchange). Then check the relay socket for spread terminals and the control wire from the PCM for continuity (under 0.5 ohms end-to-end). Live data: watch RAD Fan Command and Engine Coolant Temp; the fan should be commanded on at roughly 199 F or with A/C request active. The expensive misdiagnosis is replacing the radiator fan motor ($150 to $300) or the PCM when the real fault is a $15 relay, a corroded socket terminal, or a chafed control wire where the engine harness crosses the strut tower.

Vehicle-specific patterns: Honda Civic D17A1 1.7L (2001-2005) is the textbook P1490 platform, with the relay socket terminals spreading from underhood heat cycling; cleaning and crimping the socket often fixes it without parts. Honda Accord K24A4 2.4L (2003-2007) sees P1490 from a failed fan relay in the underhood box, with the OE Mitsuba or Omron relay typically lasting 100k to 150k miles. Honda CR-V K24A1 (2002-2006) sets P1490 most often from a chafed wire where the fan harness rubs the radiator support, not the relay itself. Honda Odyssey J35 V6 (1999-2004) sets P1490 from the integrated fan control module rather than a discrete relay, which is a substantially more expensive repair. Estimated repair: $20 to $480.