eddieic

I've got a 2002 Civic LX with a blower motor that isn't working. Checked the fuse under the hood (I assumed it was the #4 position fuse), but didn't check any on the interior box. I saw the tutorial on how to check the resistor with a multimeter, so I did that and got a reading of 1.49 kOhms.

I checked the power at the plug that goes into the blower motor and there were 12 V detected with the vehicle on. When I tested the ground line for the plug going to the blower motor, however, I got a reading of 3.68 kOhms, which seems high to me, but I really don't know. I tested the power with a DC circuit tester, and plugging the ground to another bolt in the frame, and it lit up just fine. Will (should) it work to test that circuit by putting the ground wire of the tester onto the ground of the blower power source and testing the current there with the power on, or would that be a bad idea?

I haven't tested the blower motor on a direct line to the battery as I don't have the right wires to attempt that sort of setup. I picked up a couple of test leads tonight to try it, but the banana clips are too big to fit into the space where the (+) and (-) are on the motor, at least without the leads touching each other.

The motor does run briefly when the car is turned on and just after the car is started, but it does not operate on any speed.

My electrical knowledge is pretty lacking, so I'm really not sure if that resistance in the ground is a problem or not. Because there is 12 V getting to the motor plug, I'm assuming there isn't a problem with any of the fuses, switches, relays, resistors, etc... could that be incorrect?

I'm working now as if it's either the motor itself or a problem with the ground. I'm really not sure how the ground could have become corrupted, though. I followed the line, and I think I found in the dash where it's connected to bare metal. That would leave the motor, but I want to make sure about that before I drop $100 on a new motor.

I would appreciate any help, advice, etc you could give. I took a look around the site (at least for the 2001-2005 forum) and didn't see anything specific to this sort of topic, but if there's some thread of relevance in another forum, I would appreciate the link.

Thanks.


edit: OK, so the reason I didn't see other threads on this topic is because I had the settings wrong for what threads were being shown. With that corrected, I see there are an abundance of blower-related threads. Most of the threads, however, don't deal the the possibility of a bad ground wire.

It Wasn't Me

The blower motor fuse is #12 (40amp) not #4 (20amp). Relay #4 is for the blower motor. (located just above fuses #13 and #14 in the under-hood fuse box)
https://honda-tech.com/forums/showthread.php?t=2465423

Also check fuse #14 (10amp) in the under-dash fuse box.



Edit:

You could also give this a shot if you wanted..

1. Turn the fan switch off.
2. Press the recirculation control switch and the rear window defogger switch.
3. While holding both switches down, turn the ignition ON (II), then release both switches. The recirculation indicator and the rear window defogger indicator come on. The recirc. indicator goes off 2 seconds later and the A/C indicator comes on (if so equipped), then the self-diagnostic will begin. About 10 seconds later, the self-diagnostic will finish and the A/C indicator will go off.


- If any trouble is found, the recirculation indicator blinks the DTC (diagnostic trouble code) to indicate a faulty circuit or component.
- If the system is ok, the indicator stays off.






DTC (recirc. indication blinks)

7 - An open in the air mix control motor circuit
8 - A short in the air mix control motor circuit
9 - A problem in the air mix control linkage, door, or motor
10 - An open or short in the mode control motor circuit
11 - A problem in the mode control linkage, doors, or motor
12 - A problem in the blower motor circuit
13 - A problem in the EEPROM in the heater control panel; the panel must be replaced
14 - (with A/C) An open in the evaporator temperature sensor circuit
15 - (with A/C) A short in the evaporator temperature sensor circuit

- In case of multiple problems, the recirc. indicator will indicate only the DTC with the least number of blinks.
- In case of an intermittent failure, the heater control panel will store the DTC until the ignition is turned off.

eddieic

Thanks for the reply. I forgot in the original post that I did the diagnostic test already, and it gave 12 blinks, so a problem with the blower motor circuit. I will go ahead and check the correct fuses and relays before doing anything else.

eddieic

I checked the #4 fuse before I left for work, and it looked fine. Also found where the relay is, but didn't check it, and not sure if I really know how to... Did not check the interior fuse yet. Seeing as I have 12 V at the blower motor, does that indicate that all fuses/relays are functioning properly? Could the relay be bad and still allowing 12 V to the blower motor, but not allowing a good ground, thus causing the problems?

theineffable

it's possible that you have cracked solder joints in the relay or dirty relay contacts. you might see 12V if you did the measurement at the fan plug (w/ fan unplugged), but the voltage might drop significantly as soon as you put a load on the circuit.

btw, i'd trace down the point where the fan ground wire connects to the chassis. make sure the ground point isn't corroded.

eddieic

I will do a voltage drop test at the blower when I get home, if I can figure out how to do it. If I understand it correctly, I probe the plug on the (+) side (while it's plugged in and car "on"), record V, and then do the same on the (-). There should be around 12 V on the (+) and zero on the (-) if everything is working correctly?

If there is voltage detected on the (-), is it the motor that's bad?. If there's low to no voltage on the (+), then there's a problem with a relay possibly, or other part upstream of the motor?

If the ground is failing, will that affect any of the readings I get on the (-) of the motor??



I appreciate all the help you folks are providing.

theineffable

just measure the voltage across the blower fan when it's plugged in and turned on. if you get 12 V, there's a problem w/ the fan.

theineffable

...just thought of something...

you said you measured 12V to ground from the positive terminal to chassis. you then measured the continuity from the - negative terminal to chassis and got 3.68kohm? the reason it might be like this is because the fan might be on a negative-switched circuit (blower turns on when relay contacts connects the fan -ve terminal to chassis ground). i don't have a service manual on hand to verify this but you can easily dig up the circuit diagrams yourself. if this is the case, you have a problem w/ the circuit that turns the fan on (ie. relay or other electronics).

did some more digging around. it looks as if the "a/c transistor" is the part that switches the blower on/off. it commonly goes bad. IMO, either replace it with another one or rebuild it new parts (don't bypass the temp sensor like explained in the diy)

eddieic

If I'm understanding correctly, the resistor is the problem (this diy)? Can that be a problem if the ohms are right between the 3 and 4 pins as described here?

That has been throwing me off, because ohms were correct (1.49) between the 3 and 4 pin, but where jivi shows 0 ohm between the two pins inside the resistor, I don't think I could get a reading (open circuit). I wasn't quite sure what to make of that. I assumed that if I was getting the 1.49 kOhm reading on the plug, the resistor was good.

theineffable

there's a 3-pin transistor on the other side of the circuit board. i believe it's used to switch the blower on/off. if it's burnt open, the fan won't work (not mentioned in the diy). check the transistor w/ the multimeter in diode mode (you might have to desolder it from the board).

if you don't know how to check the transistor, find the laser-etched part number that's on the transistor then post it back in this thread...

eddieic

Alright, I decided to stop at the parts store on the way home. I saw online they had a replacement blower resistor in stock, so I decided to give it a shot. I was hoping I could buy it, check it, and if it didn't work, return it. The clerk said "no way" to that. Bought it anyway, plugged it in, and the fan ran like a champ.

So, apparently it was the resistor after all.

When I got home, I double checked the resistance between the 1-2 and 3-4 pins of the 4 pin plug going into the resistor. The 1-2 had no reading (not a zero), so I assume it is open. The 3-4 had the correct reading of 1.49 kOhms.

I did the same test on the new resistor and the 1-2 had a reading of 11.13 kOhms, and the 3-4 had the same 1.49 reading. So apparently there was something wrong between the 1-2 that prevented the fan from working.

After I hooked up the new resistor, I tested the voltage of the blower motor plug, as well as the ground. The (+) had a voltage of 12 again, and the ground had the same 3.68 kOhms of resistance, so I guess that's normal for the circuit.

Thanks for all the help guys. Even though it turned out to be "just another blower resistor problem," hopefully some of the readings I got for the bad resistor and other parts of the circuit can help someone else that runs into that.

Something I'm thinking about now is I read a lot about how a bad resistor will still let the fan operate at high speed. I did not have operation at any speed with the bad resistor. Could that be related to me having a normal 3-4 reading on the 4 pin going to the resistor, but an abnormal 1-2 reading? If I had a normal 1-2 reading, but an incorrect 3-4 reading, would that have allowed the fan to run on high speed, but no intermittent speeds? I really don't understand the circuitry well enough to have an educated guess, but it's something that came to mind once all this played out.

Again, thanks a lot for all the help and advice. I'm quite happy to have gotten this done at home without the dealership, and learned how to test some of the electrical components in the vehicle for any future troubles.

Cheers!

theineffable

that's not a resistor.

people call it the a/c or fan transistor because there's a transistor (probably some kind of mosfet) inside that's used to switch the fan on/off. transistors can fail open circuit or closed circuit. yours failed open so that's why your fan didn't work. if it fails closed circuit, the fan would be stuck on. FYI, the transistor is the 3-pin component on the other side of the PCB.

as for the diy, IMO it's good for pointing people in the right direction when their fan doesn't work but there's a lot of misinformation in there.

It Wasn't Me

You mean the power transistor? Anyhow.. that's terrific! What's funny is that I actually started to post the troubleshooting procedure for this, but thought that I may have been getting ahead of myself, so I posted the DTC DIY instead!

Well congrats on getting it fixed, but I'll let you two sort out the rest. I'm gonna "make my rounds."

Oh! And a big thanks to theineffable for the help!

eddieic

This is what I got. I've seen some call it a power transistor, others call it a resistor. The box it came in also said "resistor". What's the difference? Any?

It Wasn't Me

Was it under the passenger side of the dash? According to the manual, it's the 'power transistor'

Transistors

Resistors