Ack535

Hey all,

I am fairly new to the forum and need some sage advice. I purchased a 2007 RDX last fall. Lately, both the radiator fan and AC fan both come on as soon as you start the car, even when it's ice cold out. Shutting off the climate control unit does nothing-they still stay on. As a preventative measure, I replaced both fan relays in the fuse panel as I read that there were problems with the older relays. The new relays were the updated version.

My other thought is the coolant temperature sensor(s). I hate to take it to the dealership, but I am at a loss as to what it could be. The fans run non-stop as soon as the key is on and they will soon burn the motors out. I resorted to pulling the 30A fuses just to shut the fans off.

Any help is much appreciated!

Tomtwtwtw

If you suspect coolant sensor, try connecting a bluetooth OBD reader and downloading an app (such as Torque) to your phone. In addition to reading codes, you can also read specific engine parameters. So, you'll be able to see what the car *thinks* the coolant temp is. If you're getting a weird number or even no value at all, then perhaps the sensor or wiring in between is the issue.

Ack535

Thanks Tom, will try that.

1rdxbandit

The coolant temperature sensor is on the bottom left hand side of the radiator. 2 prongs easy to get to from the bottom.

CSmoney28

The fans always are running in the rdx ...

Ack535

I've heard that too. However, generally speaking, the fans are designed to run when the coolant temp reaches a certain point, i.e. when your stuck in traffic on a warm day. They should not be running when it's 30 degrees out and I'm doing 70 MPH plus down the freeway... I've also found that the AC is stuck on, even when the heat is on high. Makes no sense, but I have some type of electrical issue.

Altair

Actually once the AC is activated, both fans should activate, because of the control relays. Agreed, A.C. should cycle off when cruising at 30F and IF engine coolant not overheating. The A.C. relay is known to malfunction: when I got my RDX one of the first fixes was upgrading the AC relay part # "...01" (cheap online) to the "..05" new one (more $).

I know you changed both relays-which did you get? Maybe the AC one has already failed closed? In the relay box there are a couple more identical Omron, swap in one from different circuit to test for free before checking the temperature sensor from the bottom of radiator or the A.C. dash switch?

Btw, I am chasing the opposite, engine fan does not activate UNLESS I turn on the A.C... seems the SAME PART NUMBER RELAY controls the rad fan ... so now have the same relays/ sensors to recheck as you do.

Hth

Ack535

Thanks Altair, I will try that. I did replace my 2 relays with the newer OEM/Honda ones ending in 05. I'll try your suggestion and play around with the other relays. Might be worth my time to just upgrade the old Omron POS relays with the newer ones.

CSmoney28

Let me know how it works out for you

udelslayer

Just to throw this out there.

To test the environmental controls, turn the ign on to II (dont have to start).

Hold the off button on the climate control. While holding it, press the rear defrogger 5 times in 10 seconds. Release the button and it should do a self-diagnostic. It was pretty trippy when I did it, but I got no error codes on the radio.

Also, since it was so hard to find, I determined that the RADIATOR fan comes on at exactly 212f using my bluetooth plug and Torque Pro to do some diagnostics after replacing the relays. I had to drive it around a bit to make the thing go above 185f even at idle, but once it heat soaked it would stay there until the fans kicked on. I think my rad fan relay was bad but fortunate for me my wife drives with the a/c on 99% of the time which keeps both fans running at high speed. There were no DTCs and it was something I had observed for a while. The constant rad fans running keeps it around 186f, which is pretty good.

now...to work towards doing my 5th set of front axles.

cheers.

feralcomprehension

Seen this? https://www.driveshaftshop.com/driveshaft-measurement

They make a 'stage 0' axle pair for my civic that is attractively priced compared to OEM and likely to be worlds better than any aftermarket pieces. Maybe they could do the same for the RDX?