If you are measuring power at the fans, that to me is not an ecm or pcm problem. Dealer stealer now we know why they call em that. First off no ecm is going to handle a current for fans, the ecm would turn on a relay and then the relay would activate the fans. So you either have a relay going bad, or bad connections to or from the relay. I'm not an expert on hondas so that is my guess.
Check the relay then looking for bad or mouse chewed wires is where to start then look at any electrical connectors that feed the fans and the relay. You will need the manual and a wire diagram to help do the search. A quick check with a volt meter on the correct terminal for the fan relay would tell if the ecu is sending the signal to run, it must be because you read some voltage at the fans.

 

If an automatic transmission vehicle has one module that controls both the engine and transmission, it is called a PCM (such as in the second generation). If an automatic transmission vehicle has one module that controls the engine and a separate module that controls the transmission (newer Hondas), they will be referred to as ECM and TCM, respectively. If it is a manual transmission vehicle, you only have an ECM.

I agree with chidog. The story you are relaying from the dealership makes no sense.

 

Before spending $500 on an ECM or PCM, I would be asking what they did in terms of troubleshooting
Cause the ECM uses relays. Turns relays on to send power to the fans.
Would do a relay bypass test to see if it turns the fans on.
That is jumping the larger pins of the relay (they handle more current)
But, be careful not to short the ECM or you will burn it out and then need to replace anyway.

 

They said he checked the relays and they were all good.

 

The key thing is. You said there was power at the fans. That means the darn computer is just fine. And if you have full battery voltage, the problem is between the fans and the relay. Its really simple stuff.
A 1000 dollar or what ever they cost computer (pcm ecm) will not fix a corroded connector or bad wire.
IT CAN NOT BE THE LINE FROM THE PCM TO THE RELAY. YOU SAID THERE WAS VOLTAGE AT THE FANS. THAT MEANS THE PCM IS TURNING ON THE RELAY JUST FINE. The dealer shop sounds like its very dishonest.

As a side note, you said a used pcm is 550 or so. No dealer will install a used pcm, if they do the fine print will say they will not guarantee it, so if they replace it with a used one, and it won't fix the problem, then they will say you need the new or refurbished dealer part, so you could end up with a 2000 dollar investment to have them fix it. Its time to go to a honda independent shop.

 

Good advice. I wasn’t going to do it unless they guaranteed the part. I have no idea if it’s power going to the fans or the relay. I wasn’t going to get a used one only refurbished. I’m taking it to an electrical guy today to get it load tested, I might just have him figure it out honestly. I took it to a dealer because my mom offered to pay for the diagnostic fees and she is convinced that they know what they’re doing. It’s hit and miss with dealers.

 

so we are talking about your coolant fan circuit here. please realize in this circuit, the PCM does not provide power, rather it provides ground. So the reading out of the PCM should read 0V when the PCM wants to turn the fans on.

Load testing batteries - measuring the voltage of a battery with a multimeter with no loads on the battery is near worthless to evaluate the capability of the battery for starting a car. When you apply a load to a battery, the measured voltage will drop. A good battery will drop voltage less than a bad battery. The greater the load applied, the larger the drop in voltage. The 9.6V numore quoted to you by Larry is probably the voltage measured when the load was applied by his tester. Whether 9.6V is good or not depends on the amount of load applied by the tester, as well as as battery temperature.

 

I have always thought that if battery voltage drops below 9.5 volts then battery is not good enough to start engine.
As the electronics do not like that when it is expecting near 9.5 to 12 volts.
That still doesn't tell us if the ECM is good or not.
And, it doesn't explain why the fans do not work.

 

With out accurate information, we can't figure it out. We aren't there to check stuff and have go by what you tell us. Since the PCM is blamed, what is the supply voltage to it? Is it getting the signal to run the fans? I'd think some low voltage stuff would set a code. Has anyone used a capable scan tool to look? Did the auto electric guy use a bidirectional tool to turn on the fans? If they checked the relays and they are ok, then did they see it turn on when commanded? What did they do? So then no one knows what to do?

 

Another


The fans are turning on now at 214 F from my scan tool. They will not turn on with the A/C however and not sure if that’s a problem because if they turn on with the coolant temp then what what would any concern be about? Unless the air compressor builds up heat and needs to be cooled down. Don’t know how that works.

 

If the current going to the pcm is measuring 6 volts why it would be the pcm that’s the problem? The Honda dealer said it the current TO the pcm, but the work order just says AT the pcm 🤦‍♂️.

i just don’t have time to figure this out myself I’m going to have to take a gamble soon.

 

So you paid for the diagnosis and sounds like you will pay for them to replace the PCM. If it doesn’t fix it then their diagnosis was wrong and they steered you to get work done that wasn’t needed. In that case I wouldn’t be paying for that work. Seems pretty likely that this will solve the problem.

This is the unfortunate reality of owning older vehicles. Sometimes they break down. It’s still cheaper than buying or leasing a new (or even not really close to new) vehicle.

Hopefully you’ve got most of the bugs worked out.

 

I've had a similar problem when the radio was faulty. I checked the battery and found ....just by chance that the alternator was putting out anything between 10v and 13.2v..I changed the voltage regulator and problem solved!

 

Yes there are two ways for the fans to come on. One is via the radiator fan switch at the bottom of the radiator (sometimes called an ECT). This should turn on when the temp is 200F at the switch. Turning it on activates the fan relays. Since it is actually a switch, and not a real ECT sensor, it does not report any temperature number. It is just on/off. The real ECT is located on the cylinder head. My fans come on when the ECT reads 217F. Your fans coming on at 214F I would consider normal.

the fans not coming on when AC is pressed is a somewhat different problem. When you push the AC button, the HVAC control unit send a signal through the AC pressure switch, through the multiplex control unit, to the PCM. The PCM then activates the relay for the fans. If anything along that chain goes awry, the fans won’t turn on. of course, since the AC pressure switch is involved. If you have low or high refrigerant pressure that will also be something that will,interrupt the signal. I hope I got that right, it was only from memory. Pulling out the wiring diagram will show it all.

 

Ahhh thank you! I was getting really confused about those wiring diagrams. Now I understand there’s a seperate ect for reading temperature. The diagram I have says ect switch and radiator fan switch so I was baffled about what was replaced, assuming it was the radiator fan switch.
As far as the A/C sounds like an exciting journey to find out what went awry. Someone told me that if it’s low on Freon that there wouldn’t be enough pressure to activate the AC pressure switch. Well there’s no cold air blowing so maybe that will do the trick!