srose111

**important problem noted . Please read bottom.

Was troubleshooting my A/C and overheating issue. I jumped my Cooling Fan Sensor to test relay and make sure the fan was coming on. After doing this, the check engine light appeared. This is a problem 1) as a nuisance, 2) can cause you to FAIL inspection prior to registering car or renewing.

SUPER Easy fix:

1. Locate Radio backup fuse under the hood near the battery at fuse box. 7.5 amp, 2nd from the left back row.
2. With engine off and key removed- Remove fuse
3. Wait 5 min; reinstall
4. Start vehicle and enjoy the magic of a quick and painless fix.

**sadly noted day after CEL cleared by pulling 7.5a backup fuse, engine idling low at ~600-700rpm and almost dying at idle. Did some more research, welcome any comments please.... I was told bad way to clear CEL, should have used scanner, I wiped out computer idle memory. Thanks and sorry for the short lived excited post. Im not a mechanic.

*Called a dealer, they said you'd have to bring it in, hook up to scanner, and clear the Check engine light. What a waste of time, money and hassle. Knowledge is power.

civic402lx

Congratulation?
You know these info are already in the FQA stickies, right?

HondaPartsHero

Check the FAQ and pull your code. When you jumped your fan switch you actually pulled the connector off the ECT sensor which tells your ECU your coolant temp not your fan switch. Hopefully by jumping that you didn't damage your ECU.

srose111

Appreciate it. Ironically, as someone suggested, the computer actually reset the idle on its own, now at ~1100rpm after 3 rd day. Running great. However, Im still having an overheating problem where it runs up to about 80% of max. Not sure if thats normal. So when I pulled the connector off ECT that doesn't jump to test the relay? The cooling fan relay, bc it seems to do just that?

Also what exact thread or post should I check to pull the code or what you were referring to in FAQ?
I can test the ECT sensor correct with multimeter for Ohms and any resistance with no power? Continuity ?

Thanks

mk378

The temperature gauge on the dash should come up to a certain point usually about 50% and then once warmed up, stay almost exactly at the same reading through any driving conditions. If it goes up and down with driving conditions, something is wrong with the cooling system.

Fan switch is on the thermostat housing, where the lower radiator hose meets the engine. It is simply a switch that goes between open circuit when cold to closed circuit when the coolant leaving the radiator gets hot enough that the fan should be on.

If the engine tends to overheat mostly when the car is sitting still in traffic, that is usually a fan problem. Unplug the fan switch and jump the plug in the harness. The fan should now come on immediately when you turn the key on. Test drive like that-- with the fan running all the time-- and if there is no overheating, replace the fan switch.

srose111

Tried looking for that part. Do you mind looking here to see if you see part #? http://www.cheaperhondaparts.com/?p=catalog&mode=search&search_in=all&search_str=co oling%20fan%20switch

or is this it? http://www.partstrain.com/store/deta...fLjhoCaEXw_wcB

Awesome thanks. Ill def try that though before I change anything. Great idea to isolate.

Former User

The fan switch screws into the thermostat housing.

Losing coolant?

Did you already replace the thermostat?

Did you bleed the cooling system?
https://honda-tech.com/forums/honda-.../#post39830585

srose111

I thought the Fan switch is next to the radiator on R side? I thought the Cooling fan "sensor" or Water Temp. sensor is what is attached to the thermostat cover? Correct?

I did replace the thermo 4 days ago, and fully completely bled and rechecked coolant. No leaks.

Thanks

Former User

The fan switch is circled in the diagram. Unplug it and jump the connector. Does the fan run?

chrysler kid

Your fan wiring is messed up. There is no sensor on the radiator there is just a plug. The wires to your fan connector are broken, the connector is missing and you are just using the pins which might be having connection problems

srose111

Yes I have unplugged it, jumped it with paperclip and the fan immediately turned on with power as well as you can hear the relay click.

Former User

srose111

that is not a pic of my vehicle just a snap from youtube to show the radiator fan switch. My fan wiring is not messed up. I realize there is no sensor at the radiator. No connector missing again, I think you misinterpreted this pic and did read what I wrote.

srose111

I was told by someone who knows more about this than me....bad Idea. If I jump it with a paperclip that is a different gauge than the wiring, this could cause a problem in the circuit potentially at the relay /fuse and that would be a lot more expensive. I can deduce without even having to test drive that if and when the fan comes on the car definitely does NOT overheat. Thats for sure.

I think I have isolated to perhaps the temp cooling fan sensor on the thermo cover, may have gone bad again. Perhaps because it was shitty aftermarket or on the 1800mile drive with a bad thermostat it went bad again. I guess thats a cheap fix 25-32$ , or I can pull it out and bench test it in hot water to see if the Ohms / resistance /continuity check out.

Does anyone have knowledge of what the baseline Ohms are on the Thermo Cooling fan switch sensor in this pic circled in red, read cold and then when the engine is at 200F? That would help if i bench test it.

Thanks for all the input.

Former User

There is probably air still trapped in the cooling system. Bleed again as described at link I posted.

srose111

Ok will do, thanks Ron J. I have seen your post on bleeding, putting the car on incline etc. Thanks. Ill be back to let you know

Former User

Reread the instructions at the link so you do it correctly. For example, it's critical to have the heater hose valve fully open during the procedure.

mk378

As far as resistance tests, it's simply an on-off switch. Below 160 F = open circuit. Above 160 F = closed circuit.

srose111

Originally Posted by RonJ
If gas still bubbles out after bleeding as described below, then the head gasket may be blown. To check, compression test the cylinders and do a leak down test.

----------------------------------------
Bleeding the cooling system:
(may take 20-30 minutes)

1) Park the car on an inclined driveway with the front end higher than the rear.

2) Push the dash heater lever/**** to MAX heat.

3) Follow the directions in the diagram below (hint: the bleed bolt is located where the upper radiator hose connects to the engine):


Ok back after another bleed attempt. #1, there is no bleed bolt on a 2000 honda civic LX, Auto trans. as indicated in this pic. Either way, I followed the prescribed fill and bleed and although not a ton of noticeable bubbles surfaced after milking the upper and lower radiator hoses I was able to put in at least 4-6 oz maybe more. Perhaps this air pocket was in fact the entire problem not the ECT. Ill know after next drive in traffic.

Q: the heater is supposed to be full blast with fan on full blast correct??? (during the bleed)

Q: the amount of fluid in Reservoir went up during this bleed, is that expected or tell anything?

Q: is it worth taking to mechanic to "pressure test for leaks" the radiator system? No visible leaks are noted.

Now waiting for engine to fully cool and see if any fluid was pulled into the block.

thanks again for troubleshooting this, please cont to add any feedback

chrysler kid

Temperature just needs to be set to full heat, the interior fan doesn't need to be running, amd the radiator cap shoild be removed. As it gets up to temperature the air pockets are forced into the radiator and out the radiator cap. Technically with the resevoir empty it will bleed itself, but we give you the full procedure to make sure everything is done correctly.

You are essentially forcing coolant to every passage way and once car has reached operating temperature the thermostat opens and any air inside the engine is forced to the highest point in the cooling system, with the car on an incline this should be the radiator cap opening.

As mentioned before you can jump the switch with a paper clip. The switch itself has a copper spring inside of it that expands and contacts the housing at 180 degrees to complete the circuit to allow the fan to turn on and receive power. When you use a paper clip to jump the wires it can not damage anything because it is completing the loop itself, so it runs like it should when the sensor reaches 180 degrees.

Most switches work the same way, using a spring that is sensitive to heat or pressure to provide resistance, or connect current, so the voltage reading can be interpreted as a pressure or temperature reading. The radiator switch on the thermostat is the simplest one, it's either on or off. The switch could have an internal fault and not be conducting electricity correctly

Drive with a paper clip in it and if the car doesn't over heat you know the switch is bad. If the car overheats with the fan running constantly you know you have another more seriois problem

srose111

@mk378 I sent you a PM, any additional thoughts on this?

srose111

Can you clarify what it means..."make sure heater hose valve fully open?"

Former User

Full heat on climate control (fully open heater hose valve).


Verify in engine bay that valve moves to fully open position.

srose111

Ok, got it. Ill check that. I did that on my bleed, minus checking bay for mvmt.

So I just drove for 45 min, its not that hot out, but nonetheless i drove some big hills and had the A/C running. The thermo gauge didn't move one fraction off 50%. Don't want to celebrate too early, but I believe you may have solved it with a thorough and patient bleed of the system, since I was able to add a full 6 oz++....the level wasn't moving much, but every time I squeezed the hoses, it would drop about 1inch to the neck of fill spout, then Id top off, then it would drop.....so that could have been the whole deal.

thanks

Former User

Good luck.