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Rick
Rick, Nissan Master Technician
Category: Nissan
Satisfied Customers: 503
Experience:  27 Years working in Nissan Dealerships Currently working for Nissan Dealer
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Maxima: 1996 Nissan maxima with auto air lost blower motor.

Customer Question

1996 Nissan maxima with auto air lost blower motor. Blue white wire has 12 volts at fan, and at fan control amp. black wire has a good ground at the amp. signal wire tests at 9 volts to ground. attempted to replace main control unit and the fan amp 3 times. each time the amp is replace it pops(not a fuse the amp itself) I have researched the wiring diagram and not sure where it is shorting out from. Can you please help..
Submitted: 1 year ago.
Category: Nissan
Expert:  Rick replied 1 year ago.
Hi my name is***** will answer your question the best I can if I have helped please remember to leave a positive rating
I'm wondering if your blower motor is good or possibly drawing too much amperage when its turned on from the blower motor amp and that is causing the amp to pop. you could try bypassing the amp by providing a ground to the blue white wire at either the motor or the amp and the blower should come on full speed, having 12 volts at the blue/white wire is normal as it feeds through the blower motor from the brown/white wire that is coming from the fuse, the 9 volts on the signal wire sounds normal and the transistor in the amp just makes the connection to the ground on the black wire
Customer: replied 1 year ago.
Already remove blower motor and provided power and ground. It operated fine. After reinstalling tested for power at motor. All good then jumped a ground and it worked at full power. Also to mention previous owner made a jump connection from cigarette lighter to operate fan. Replaced fan last year so unsure if its the blower motor.
Customer: replied 1 year ago.
Also jumping power to ground at the amp to bypass only blows the fuses for the fan.
Expert:  Rick replied 1 year ago.
So are you saying that the blower isn't getting power from the relay its getting power from the cigarette lighter?
Customer: replied 1 year ago.
No I reconnected stock wiring and removed the other. All stock now
Expert:  Rick replied 1 year ago.
I am working on the issue your having I'm going to post the wiring diagram and possibly another solution if you can give me a few minutes
Customer: replied 1 year ago.
Sure
Expert:  Rick replied 1 year ago.
I don't know why the fuses should blow if you ran a ground to the same blue/white wire at the blower motor amp, that seems strange, but here is the wiring diagram and it may be that the auto ac amp that is built into the BCM may be the problem, if it is and you have to change it you may need to reprogram all the keys to be able to start the car
Expert:  Rick replied 1 year ago.
Take a look at the diagram see if it helps. I'm going to have to go back to work I'll check in on you this evening when I get home
Customer: replied 1 year ago.
Same here thanks
Expert:  Rick replied 1 year ago.
talk to you later
Expert:  Rick replied 1 year ago.
I am wondering which fuses blew when you grounded the wire at the blower motor amp, and I have a ridiculous question, were sure the blower motor amps that you changed are the right ones? they should be a solid state device with an aluminum heat sink and not just a set of resistor coils
Customer: replied 1 year ago.
Yes I know the difference between a resistor and the fan control amp. And the fuses blowing are the fan fuses.
Customer: replied 1 year ago.
Couldn't get to it tonight and run through tests with a clearer pic of the wiring diagram. Worked way late.
Expert:  Rick replied 1 year ago.
do you get anything other than 9 volts at the signal wire to the blower amp, because it should be between 2.5 volts and 9 volts depending on the fan setting of the control head. 9 volts would be for full speed
Customer: replied 1 year ago.
No it never changed. Even with a different control head and varying the speeds.
Expert:  Rick replied 1 year ago.
I think that could be an indication of the auto ac amp (BCM) being shorted internally which could be why the fuses blew when adding the ground at the blower motor amp. Ive uploaded the whole section of the manual for heater and ac, there is a self diagnostic to the auto ac, its complicated to use but it might help with this diagnosis how to enter self diag mode starts on page 70 and one of the last tests it has you do is check the voltage for the signal wire and it should vary between 2.5 and 9 volts
Customer: replied 1 year ago.
If it is the bcm where is it located? And would I really have to replace the keys as well? It's a 1996 and the keys don't appear programmed.
Expert:  Rick replied 1 year ago.
Its located under the radio and heater controls, and you wouldn't have to replace the keys just reprogram them it depends on the NATS system on the car since its an older car its probably NATS 2.0 and you may not have to do anything with the keys
Expert:  Rick replied 1 year ago.
Well time to go to work
Customer: replied 1 year ago.
Ok. I'll try and look at it tonight. Will be late.
Expert:  Rick replied 1 year ago.
Okay your particular problem is something I haven't seen before so I'm interested in what the problem is
Customer: replied 1 year ago.
Yes Ty. I'm an auto tech as well. But don't have much access to info as you seem. Btw is the bcm the module on the floor board behind the radio?
Expert:  Rick replied 1 year ago.
you have two modules there one is the bcm and the other is the a/t control unit here's another picture showing the location
Customer: replied 1 year ago.
It has a manual transmission. So I guess that's the only module there. Where would the ECM be?
Expert:  Rick replied 1 year ago.
Yes it should only have the BCM
Customer: replied 1 year ago.
Didn't forget you. Been raining a lot here in San Antonio. Can't even replace the brake hose and master cylinder on my f150. I do think I have a good idea. PO said had to replace the ECM. Considering the fan was hard wired to the cigarette lighter I think the other mechanic not tech thought the bcm was the ECM. I bet it's a bcm for manual climate control. Would that cause this problem?
Customer: replied 1 year ago.
It's asking me to rate you and you've been a great help but can I wait till its fixed? If that holds you back from pay I can try something. Just want us both to learn from this ya know.
Expert:  Rick replied 1 year ago.
Well if you had it working after you rewired back to the correct way then the BCM would have to be correct, if that's not the case and the PO did replace the BCM with a unit for manual air then it probably wouldn't work at all. If you rate me now or later it doesn't matter you can still post to this question so we can still work on the problem, if you want to wait that's fine I think the question will stay open as long as we keep communicating
Customer: replied 1 year ago.
Great I think it's the bcm is sending a constant
Customer: replied 1 year ago.
Hence why no signal variance. Bcm for a manual climate control
Expert:  Rick replied 1 year ago.
Actually I took a look at the wiring diagram for the manual air and it doesn't even use the bcm for any of the a/c or blower controls, on that one its all controlled with the push button control head and a rotary switch for the fan, its much simpler
Customer: replied 1 year ago.
Ok was afraid of that. So back at square one. Gonna run the bcm numbers on google and go from there. Also run to junkyard for another fan control amp and a bcm if numbers don't match. It makes sense the Hugh vtage though
Customer: replied 1 year ago.
High voltage. Phone sorry
Expert:  Rick replied 1 year ago.
Okay I'll keep looking to see if I can come up with a solution but I think because the voltage doesn't change from 9 volts on the signal wire it probably is the bcm
Customer: replied 1 year ago.
Same here
Customer: replied 1 year ago.
Wrong bcm
Expert:  Rick replied 1 year ago.
If you think the bcm is wrong post me the part numbers on it and I can have my parts dept look it up to see if its right
Expert:  Rick replied 1 year ago.
I was just thinking about the problem and since the power for the blower motor goes through the blower motor and the ground is provided on the other side (blue/white wire) if you checked for power at the blower motor amp with the blower motor disconnected there should be no power on the blue white wire and if there is then its coming from the bcm where it would be shorted internally to the fuse for the blower motor relay
Customer: replied 1 year ago.
Got the bcm # ***** check. 284914ou1o
Expert:  Rick replied 1 year ago.
I won't be able to have my parts man check the number until Tuesday when I go to work again, so I'll check then and post what he tells me
Customer: replied 1 year ago.
Ok
Expert:  Rick replied 1 year ago.
I'll be in touch Tuesday
Expert:  Rick replied 1 year ago.
My parts dept says that is the right part number for the bcm

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