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Discussion Starter #1
I have a 2007 CRV that overheats a bit when I get stuck in traffic. I’ve flushed the coolant, swapped out both coolant temp sensors, tested the thermostat.

The problem (I think) is that the fans won’t kick in until engine temp is around 212/215 (from OBD reader) and they won’t stay on longer than 10-20 seconds. And it’s always both fans that turn on at the same time. The fans work as expected when the AC is on.

Questions-
1. I’ve read that the fans should engage in a sort of sequence (radiator fan at lower temp setting then both fans at a higher setting). Is that right? And if so, what does that say in terms of the culprit here?
2. Are the fans triggered by a temp threshold at the engine coolant temp sensor (for which I get a reading through scan tool) or the radiator one (for which I don’t seem to be able to get such a reading)?
3. The engine runs at perfect temp consistent (194-198) if I run the car in a lower gear (2 or 3 in traffic). I know decreasing the load helps cool down the engine but I’m wondering if there’s something off with my transmission.
 

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In the service manual, it says to first check fuses and relays in the under-hood fuse box. Also check the harness connectors to make sure they are not loose or corroded. Also check to see if there are any DTCs (codes). There is a fan motor relay and a fan control relay, and the #7 20-amp fuse is for the fan system. There is a low-speed and a high-speed fan circuit. It sounds to me like the low speed is working t least partially. If it is not working fully you could have a bad fan motor. If both fans are working (you can run a 12v jumper to each unplugged fan motor to check) then I would guess the fan control relay is the issue. Emphasis on the guess part. If I read it correctly, the computer ECM decided when to kick the high fan speed on based on engine temp. So if the fan work then I would try replacing the fan control relay first. In the under-hood fuse/relay box, the top horizontal row of relays are, left to right, radiator fan relay, A/C condenser fan relay, and fan control relay. Any one of those could be causing the issue, but I would pick the top right one first (fan control relay). IIRC these relays are about 13 bucks each or so. Let us know how that works out.
 

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If both fans turn on when the AC is turned on, then I believe the relays are good. Don't waste your money on relays. You usually can just switch two of the same relays (usually there are several identical ones in the relay/fuse box) instead of spending your hard earned money and precious time driving to a store.
If both fans turn on at 212F or so (They both go to Hi Speed at that temp.) , that means the one temp sensor is working properly as well as the relays. They probably turn off fairly quickly because the temp drops rapidly with both fans on. I would jumper the connector at the temp sensor that you replaced at the bot of the radiator, I believe and then turn the key to ON and see if the radiator fan starts up and runs fine. If you put in a cheap sensor, it may not be good. If that jumped connector doesn't work, then it could be the wiring itself or a connection in that circuit.
Still, I don't have a wiring diagram for the 2007 CRV so I am just generalizing using the 2000 CRV Service Manual as reference.
If it starts to get hot in traffic, turn the AC on which will turn the fans on. Short term fix for overheating.
Buffalo4
PS: https://www.youtube.com/watch?v=TCKD7g82bJc for a reference.
Whoops, not a real good vid but some searching on youtube will get you going.
 

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Discussion Starter #5
Replaced the fan control relay - still the same issue. Also swapped around the relays for the AC + radiator fan relays - didn’t fix it either.

Should both fans turn on when the AC is on? Or just the AC fan? I’m asking bc, over the past couple weeks of troubleshooting this, I’ve never seen only 1 fan turn on. It’s always been both or neither.

About this suggestion:
“I would jumper the connector at the temp sensor that you replaced at the bot of the radiator, I believe and then turn the key to ON and see if the radiator fan starts up and runs fine.”

I’m ok trying this next, but are you sure the sensor at the radiator is the switch for the fan (as opposed to the sensor at the engine)? And what’s the easiest way to jumper the connector?
 

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There are two sensors in the radiator fan circuit. ECT1 sensor is located next to the thermostat, and ECT2 is located bottom center of the radiator. Both sensors are used in fan activation. However:

It may be possible that the low speed fan operation is not working. Check fuse #36 (10amp) in the under-dash fuse box. If it is good, pull and test the A/C Diode #A from the under-hood fuse box. If neither of these is the culprit there is a good chance you either have a loose connection in the A/C fan circuit, which is a completely different circuit from the radiator fan circuit, or, even more likely, a bad or poor ground at one of the ground points in that circuit. Both circuits need to be fully functional in order for fans to work correctly. I would check all the grounds in both circuits. The troubleshooting sequences for all this is in two separate sections of the service manual, and is quite extensively step-by-step and complex, so I highly recommend you get a service manual. It could easily pay for itself with just this repair. I got my manual in CD form off eBay. Someone said it is also available from Helms (?). Hope this helps.
 

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Discussion Starter #7
Thank you

I got Haynes book from autozone. Is that what you mean or something official from Honda?
 

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That diagram is for the fan control when using the AC. It does not show the fan switch which turns on the radiator fan when the temp gets to around 194F + (when the AC is OFF) and, I believe, that fan switch is mounted on the bottom of the radiator on your yr CRV, or it may be mounted on the thermostat housing. Look it up.
So, I do believe that that switch is faulty or the connector or the wires are faulty. To bypass that switch, you can try jumpering the contacts in that connector and THEN , turn the ignition switch to the ON position and see if that fan now goes on. If it does, the switch is bad, whether it is new or not.
Buffalo4
 

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Discussion Starter #12
“That diagram is for the fan control when using the AC. It does not show the fan switch which turns on the radiator fan”

It may not be clear in the image you see but it does show the ECT switches at the bottom of page as inputs into “ECM” and has a “low fan control” in the ECM box. I think this is fan control for both AC use and temp based operation.

Your point that the ECT2 at bottom of radiator is faulty (or its wiring is faulty is well taken). I doubt the switch is bad bc I got it brand new from Honda. But I’ll jumper the connection to dbl check the wiring.
 

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Discussion Starter #13
On a highway drive this morning I noticed temps behaving the same way they did in the city (inch up to 212/214 then quickly drop down to normal). I couldn’t hear if the fan turned on or not. I’m wondering whether the problem is actually the thermostat.

I know it opens because the lower rad hose does get hot, but I’m wondering if it’s opening at a much higher temp than it should.

Anyway, I’m setting aside some time this weekend to work on it- we’ll see. Any guidance welcome as always
 

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When it starts to get hot, turn the AC on. That will turn both fans on. If that doesn't help, then it may well be the thermostat. If turning the AC on helps, then it points to a fan control problem.
Buffalo4
 

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Discussion Starter #15
Turning AC on immediately drops the temps when I’m idling, drops the temps a bit when city driving, and not so much on highway driving (dropping to 3rd gear is what helps on the highway)
 

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Discussion Starter #16
Tried to jumper the temp switch wire and it didn’t work (got a p2184- low current circuit). Also ran the car without the temp switch hooked and something interesting happened - the fans turned on at 203/204 instead of 212/214. I did this 4-5 times and got the same result.

I also tried to replace the thermostat but one of the screws was too rusted so rather than risk stripping I’m gonna buy some new screws and try again next weekend.
 

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Fans should kick on at about 212. That's about the avg point for cooling fans to engage fully on 90% of cars out there. The reason its engaging sooner is that its using other sensor data to engage them.

If fans function then I would have started with the thermostat. Judging by what you have said it sounds as if its not opening when it should or only partially opening.

But turning on is one thing, they should kick on when idling so be under the hood when they do, should be moving a lot of air when they engage.

Also make sure there is no debris in front of the condensor/radiator blocking the fins.

You said you replaced both temperature sensors, are they Honda/Denso etc or stuff offline or from auto parts store? Online especially is a bad idea. Better to get a used one off a motor at a junk yard than cheap stuff offline.

In your original post you said something about transmission. YES IT CAN CAUSE THESE ISSUES. Has it been properly maintained via drain and fill, not flushing? If your transmission isnt working properly it could be putting excessive load on the engine as well as transmission itself can be getting too hot. Both will cause high temps at idle while in gear.

Sent from my SM-G950U using Tapatalk
 

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Discussion Starter #18
Thanks for the reply.

There’s some debris lodged in the fins but nothing too bad I don’t think (based on pics I’ve seen online).

Both new censors are Honda and both are new.

As to the transmission - I just drained and filled the transmission and the fluid didn’t look great (plus there was some white crap at the dipstick tube). I’m not sure how the PO maintained the transmission - I bought the car at 100k and it’s now at 130k. From what I can tell from the cars operation / condition, it seems to have been at least somewhat well-maintained. The car certainly feels sluggish to me while in D, but that doesn’t explain why the fans aren’t kicking in at 194 and why they didn’t kick in when i jumpered connection.

I also just bought the Helm service manual for the car. The Haynes I got from Autozone was good but I’ve reached the limit of its usefulness
 

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Discussion Starter #19
So I’m now convinced I have two cooling system problems.

#1- The fans don’t turn on at low speed setting. This is looking like an electrical problem. Got the diagnostic tools and getting the helm book tomorrow. I’m not worried about this issue as much bc i can pretty much keep temps at 190-198 by driving in 2nd gear. Which is about right for rush hour traffic in DC. Putting the heater on drops temps to 180s.

#2- this is the one I’m really worried about. I’m overheating a bit at highway speeds. 208-215 degrees when I’m in gear D (back to that in a second). Today I replaced the thermostat. Confirmed it works by dropping in 180-200 degree water before I put it in the car. Actually compared it with the old one, and turns out the old one opens a bit later and more slowly. There’s nothing blocking air flow into the radiator and i hosed down both the condenser and radiator. Also used infrared thermoter to get temps across the radiator. Very top of radiator matches the temp at ECT just about identically (about 10-20 above top hose temp). Temp drops more or less evenly as measure down the radiator (though I couldn’t get great angles towards bottom of the rad). Bottom hose measure about 20 degrees less than top hose. If I turn on the heater at highway speeds (60-75) my temps drop about 5-10 degrees. If I drop to 3rd gear I’m back to normal- 194-198, despite the fact that I’m at 3500-4000 RPM. Any ideas for next steps here? I’m thinking my radiator is fine. water pump?
 
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