alex_nyc

Hi everybody! So my 2003 CIVIC 2DR EX 1.7L D17A2 has the Coolant Fan Stuck on. (not the AC fan).

When I disconnect the coolant sensor (up by the thermostat) the fan turns off. Does this mean that the sensor is bad and that the relay is not causing the fan to stay on? (the engine has been off a while and never overheated)

edited

ezone

That would make me believe the sensor is stuck on.

alex_nyc

thank you! and at what temp does the fan turn on?

I can use an OBD2 Bluetooth tester and a temp gun on the housing to test this.

ezone

I have a diagram that shows it turns on the fans at 199*F.

The scanner should not be your bible on this one, the temp sensor it reads is temp of coolant exiting the engine (upper hose).

The fan switch senses the temp of coolant exiting the radiator (lower hose).

They can be quite different temperatures during normal use.

HTH

alex_nyc

I had disconnected the coolant sensor at the upper hose. Is there a sensor on the lower hose? Where is the sensor located that is possibly bad?

thanks

ezone

Don't overthink this just because I ramble about what's there LOL
It's the one you unplugged that got the fans to shut off.

If you were to study how the thermostat housing is constructed (plumbing of the water pathways) it contains inlets and outlets for both engine and radiator all in one unit. The smaller sensor on top measures engine temp for the computer to use (and would set a code if left unplugged), the sensor pointed toward the front senses the temp of water exiting the radiator and controls the fan.

alex_nyc

Ok Got it! Thanks!

alex_nyc

I replaced the defective coolant sensor with a new $6 pepboys one and now the fan comes on like it should. It also runs cooler as per the gauge indicator.


Thanks for your help!

ezone

$6 ??? I guess if it works more than a week you got your moneys worth LOL