Hello, I am dealing with an overheating problem on my 06 Acura TL. I will try my best to give all the information regarding this issue. Any help is appreciated, and sorry if this turns into a long post. I just want to be as thorough as possible

To preface: I had an overheating issue around a year and a half ago. Replaced all fan relays, radiator fan, and water pump/timing belt around a year ago. Turns out it was the small radiator fan fuse Once I replaced that, everything was perfect.

Fast forward to now, and I noticed the temp gauge was a little above middle last week, so I turned the heater on to lower temps. When I got home, I noticed the coolant in the rad was low as it boiled over into the reservoir and bursted out during overheating. I also noticed the radiator fan only turns on low speed when the A/C is on. It does not turn on otherwise, so I replaced my coolant temp. sensor which was under warranty from the last time I changed it a year and a half ago. I verified the fan did not turn on high by using an OBD II app on my phone paired with a bluetooth OBD II reader to measure coolant temps from the sensor, and it got up to 212 F on my way home from work without the fan turning on high speed.

What I have done so far:

• I have tested all fan relays, the 3 black ones in the under hood fuse box. All click on with 9 volts and all have continuity when tested with a multimeter while powered. I also checked and replaced the small rad fan fuse that burnt out last time.
• I have replaced the coolant temperature sensor.
• I have followed the service manual steps, and the results are as follows:
  1. First I tested the relays, they work
  2. Next, I measured the voltage from rad relay socket 1 and ground, I got 12 volts
  3. I inserted a jumper wire into the rad fan relay sockets 1 and 2, and the fan engaged.
     • I could not tell if it engaged in high speed, although it is my assumption that only high speed would have engaged with this test, so I think this is working normally.
  4. Lastly, I measured voltage between rad fan relay socket 3 and ground, I got 12 volts.

With this test, the service manual states, "Repair an open in the wire between radiator fan relay 4P socket terminal No. 4 and the engine control module (ECM)/powertain control module (PCM).". Now, I have two main questions:

1. Is it possible that the issue lies somewhere else?
2. If the problem is indeed an "open" in the wire between the relay and the ECM, how can I find more info on what to actually do, or is this a job for a mechanic?

Also, as a last resort/to save some money depending on estimated repair costs, is it possible to just wire a switch to bypass the relay, and run the fan on high every time the coolant gets up to temp? If this is an option, has anyone done it or have any guidance on how to do it? I watched a youtube vid about some sort of switch to the relay, but many comments stated their relay box caught on fire lol

Attached is the service manual troubleshooting guide I followed:

 

The best way to test the fans is to have bi-directional scan tool. It allows to command the ECM to turn on the fans. If they don't work, then it's relatively simple to check what's wrong with the system.
If you don't have scan tool, then it might be possible to trick the car into thinking that it's overheating by connecting some resistor instead of coolant temp sensor.
Usually higher temp = lower resistance, but jumping it to 0 ohms will turn on check engine light. Although it might force fans to high as well.
Sometimes disconnecting the sensor will also force fans to high.

From your description it seems that you did pretty good job and in fact there is a problem with a signal wire from the ECM.

One thing that I could pick on is that some systems should be tested with voltmeter, and others with a load.
However, since you did jump the relay and fan was running, then everything on "high current" side should be good.
I would put a test light between ground and #3 instead of measuring the voltage. Make sure that this circuit can supply enough current for relay's coils.

It is possible that something happened to the wire going from the ECM to the relays, or that ECM is bad internally (one of transistors used to control relays is bad). When fans are commanded on, I would put test light between power and #4. If light doesn't work, then test directly at ECM. If still nothing, then ECM most likely bad.
But once again, to test that you need to be sure that fans "should" be on.

One thing you could also do is to ground the control wire directly at the ECM. If all of the circuit is good then both fans should kick in on high when you do that.
If both fans run, then ECM is broken internally.

 

First of all, sorry for not responding for a bit, life happened. And thank you so much for writing a very descriptive reply.

So, I finally got a chance to buy a test light and test the relay #3 socket. I did that, and the light lit up, so good news, right?

I then replaced the radiator fan relay and connected about 5, 1k ohm resistors into the socket for the engine coolant sensor, and the fans eventually turned on, both of them. (Admittedly, I just kept adding 1k resistors until it turned on, I have no idea how resistors work or if they are additive or not, but apparently they are). I also tried with a 10k resistor and nothing happened, but that's besides the point..

Lastly, I noticed that once I removed the resistors and left the connector unplugged from the sensor, the fans both turned on high as well and the dash read accurately that "the temp" was in the red zone, since no resistance. I also got a check engine light - just as you predicted lol - that did not want to clear right away.
Note: All of this was done with key in accessory mode, and the A/C turned completely off, as well as the car being cold.

I have also yet to check the ECM testing that you suggested as I do not know where to locate that, and I wanted to try your previous suggestions first. I may have a chance to try that this weekend, if necessary.

So now my question is, is there even a problem? I have yet to drive it extensively, as I do not have a chance until this weekend. I am wondering if maybe my coolant was just low somehow and that caused the overheat and splashing over of coolant... I will confirm this theory when I get a chance to drive it long this weekend. What are your thoughts on the fans turning on with the sensor connector having resistance/being unplugged, and with the relay connected?

As a side question, do you know when at what coolant temp the fan is supposed to engage? It read as high as 212 F without turning on, however the coolant temp gauge read normal, so maybe that is normal temps?

 

Depends how you connect them.


Think about electricity and resistors as water pipes with restriction. If you connect them in series, their resistance sums up since "water" must flow through all of them.
If in parallel, some water can flow through first, some through second, etc. so overall it's easier to flow.


Also both fans will always work in pairs. Either on low or high setting. But TL will never turn on just one fan. If one is not spinning then something must be broken.


You meant key on engine off right? In ACC only the radio should be working.
Anyways, that is usually the default behavior. Computer sees that something is wrong with the sensor and it's safer to have fans run on high all the time than don't run at all when they might be required.

If fans turned on high with resistors or ECT (enginie coolant temperature) sensor unplugged, then there's no reason to test ECM. Fans running on high proves that ECM can control fans.
Actually that proves that all (except for the unplugged ECT sensor) of the electrical side of the cooling system (fans, fuses, relays, ECM, etc.) is in working order. Or at least that it worked in that moment.


Good question. Seems like system behaves like it should. No idea why it overheated. If thermostat fine, and electrical side of cooling system fine, and coolant level fine, then there's not many things left.
Most common things left that come to mind are either restriction on coolant flow, like plugged radiator, or restriction in air flow through the radiator, like bunch of tree seeds / leafs / other stuff stuck to the radiator, or damaged fins, or incorrect coolant mixture. If you use original honda, it comes premixed 50/50, so that doesn't matter.
But it you buy concentrate and don't mix it with water car will overheat.
First thing that you can see when you look through the bumper is actually condenser - radiator for the refrigerant in the A/C system, not for engine coolant. But if that's badly plugged for whatever reason airflow through radiator will also be limited.

On TL, fans should run on high if coolant temp is >206F (97C). Thermostat begins to open 169-176° F (76-80° C), and should be fully opened at 194° F (90° C).

Technically water shouldn't ever get above boiling point, but having bad radiator cap might cause coolant reservoir to overflow. (well it can also be caused by bad head gasket but let's not go there yet hah)
Also it's pretty common for that small hose between radiator and coolant tank to leak. I replaced mine and it kept leaking so I put hose clamp on that small hose where it connect to the radiator and leave coolant reservoir cap slightly loose so any air can easily escape.

So overall I guess you need to drive it again and try to catch it in overheating situation and figure out what's happening.

What's the ambient temp where you live?