# Alternator or Computer Problem? (Alarm goes off on its own + more problems)



## HalfJoey (Jun 29, 2008)

About a year and a half ago my 1997 Nissan Pathfinder’s engine would just off and steering lock up out of the blue, but the power would stay on. I took it to several places and spent a lot of money not fixing the problem. Finally one shop found the problem to be the PCM Relay. They replaced my PCM relay and my car no longer had the problem; however, it got some new problems. 

A few days after the problem was “solved” my car started to do something funny. When I was the driving my windshield wipers would go off once on their own, and this would happen maybe once or twice a day, sometimes it didn’t happen at all. When they go off im not able to use the first wiper setting.

A more recent development is my car alarm going off on its own. In the 7 years I had owned my car I never heard the alarm go off for any reason. When I was sitting at work I heard an alarm, looked out the window, and my alarm was going off. This happens a few times a week only during the day, but recently its been happening late at night after I haven’t touched my car for hours. When it goes off on its own im not able to lock my doors with the keychain control. I often now just keep my door unlocked if I think the alarm will be a problem…

Another small issue that could be related: One night I parked my car in the garage and noticed when I pressed the gas while in park my headlights would get brighter to dimmer as the RPMs rose and fell.

I’ve been living with this problem for a year and a half now because im afraid to take it to a shop that will charge me hundreds of dollars on something they are not even sure about.

I’ve asked around about the problem and I get two answers, “Its your alternator, change it out” or “It sounds like a computer problem” Does anyone know what it could be?

My car just hit a milage of 90k.

Thank you,

P.S. I’m really happy I found this forum. I hope to become a more contributing member and help learn about my car more. If you need a cliff notes version just let me know and i will make one.

[edit/ CLIFF NOTES]

A shop changed out my PCM relay.
- Soon after my windshield wipers wipe on their own at random times
- Car alarm goes off on its own at random times
- Sometimes my light brighten or dim in relation to my RPMS
- Is it an alternator or computer problem?
- Could it be a PCM relay problem?


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## 88pathoffroad (Jun 6, 2004)

Is it the stock alarm or is it aftermarket?

Have your alternator tested at an auto parts store, they do the testing for free...


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## HalfJoey (Jun 29, 2008)

Thanks a lot for replying. The alarm is stock.

I will go to AutoZone or Checkers to have it checked on Saturday.

If the problem doesn't always occur do you suppose a voltage reader will still notice a problem? 

Weird Thought:What if i bought a voltage reader and ran it into the inside of my car while im driving so i could monitor the voltage while I drive; to spot any fluctuations. Is that something that can be done?


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## TheCROW163 (Mar 1, 2007)

Just a thought about the alarm going off by itself. I know for sure that you cannot lock your doors with the remote only when one of them is ajar. This means that the little switch that the door presses on when it closes is not functioning correctly (or it's rubber housing has deteriorated). This would explain the alarm going on by itself and your not being able to lock the doors using the remote. Check if the cabin light is on when this happens, it will definitely confirm this.
Check all the switches of the doors and hatch.
Hope this helps.


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## IanH (Feb 11, 2003)

Thats a really good sugestion.
Re: the light getting brighter with rpm, this could also be a sign of a failing battery, get your battery checked also. but NOT normally an alternator failing, voltage rises to 14.4 V approx at higher rpm as the Alternator puts out more current to charge the battery. 
If battery is good it will be close to 14.4 at idle.
If you don't have a simple voltmeter/multimeter i suggest you get one, digital, under $10 is ok.
You can check battery with everything off, should be around 13V if good and fully charged.


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## HalfJoey (Jun 29, 2008)

I just got back from AutoZone. They ran a battery/alternator test. I couldnt see the exact voltage, but the man first said my battery was dying but it was still under wanrentee so he replaced it for free (nice) Then we ran another test and my voltage was still real low (he didn't say how low and i couldnt see) He then determined that my alternator was bad. This is good news imo, but may not solve my cars overall problems I suppose.

He just clamped a machine to my battery, then i turned on my car and sometimes put the engine to 1500rpms. Is this a correct way to test it? I was thinking about picking up a voltmeter myself to test it out before I take it to a place to get a new alternator or change the alternator out myself. Mulimeter at Home Depot, Good?

I guess my next questions is if there are any tutorials online on how to change out a 1997 Nissan Pathfinder alternator? I've seen video tutorials with other cars. I hardly know anything about cars, but i have an ok grasp on the basic internal workings and everyone tells me changing out the alternator is easy. 

Thanks a lot for all your help guys! Let me know if you have any further tips.


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## IanH (Feb 11, 2003)

yes thats more than good enough. Is there a harbor Freight near you, they have them from about $3.....
well its there job to sell parts, but it shouldn't be a secret what they are doing and the readings.
No, Alternator output increases all the way up to 5,000 rpm or so, but you get 50 - 60 % at 2000 rpm and enough at idle to not discharge the battery under most conditions.
So if the battery is discharged the voltage will be held down.
download the FSM from phatg20.net and read the Alternator remove and replace instructions.
ITs not hard .. only awkward to get at the nuts and bolts......


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## HalfJoey (Jun 29, 2008)

I just looked online and there is a Harbor Freight very close to me, I'll be there tomorrow to get a meter and test my car myself. I'll read up on how to do it before I get started. Is it possible for me to stay in the car while I look at the meter? I'll have a friend come over.

I downloaded the FSM for the 1997 Nissan Pathfinder and i cant seem to find an alternator section, I only glanced through it, so ill keep looking for it tomorrow.


Is this an ok Multimeter?

I'm kind of getting excited about changing my alternator by myself.

Thanks,

[edit]

I was looking around the Harbor Freight website and found this Battery/Alternator Tester Too good to be true?

[edit #2]

I notice it says 12v system. I need at least 20v, right?

[edit #3]

Once i get this Voltmeter I will test the Alternator and the Voltage Regulator. I'm checking on different sites on how to tell which is broken and how to test them. WikiAnswers has a lot of answers, except some of them are horribly written.


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## IanH (Feb 11, 2003)

HalfJoey said:


> I just looked online and there is a Harbor Freight very close to me, I'll be there tomorrow to get a meter and test my car myself. I'll read up on how to do it before I get started. Is it possible for me to stay in the car while I look at the meter? I'll have a friend come over.
> 
> I downloaded the FSM for the 1997 Nissan Pathfinder and i cant seem to find an alternator section, I only glanced through it, so ill keep looking for it tomorrow.
> 
> ...


Well I have written about this many times on here, its straight forward.

Test battery voltage everything off and cold.

Should be 13.2 V fully charged. Range is 10.8 fully diss-charged to 12.0 half charged, 13.2 fully charged.
So If 11.0 v either very flat or one bad cell, so a typical pre condition is to either put on a charger in garage or make sure alternator is charging.

ie 14.0 - 14.5 V, low load, running 3000 rpm or so, should be stable with rpm above say 2000.


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## IanH (Feb 11, 2003)

You can look at the voltage in the car, you will need longer leads or use the cigarette lighter outlet and wire up to the meter, thats what the tester with LEDS does, uses the cigarette lighter outlet. but its easier to read the meter and work the throttle cable under the hood. RPM is not that important, you can guess and it will be fine.


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## HalfJoey (Jun 29, 2008)

Update:

Thanks for all your help guys, unfortunately I still cant solve my problem. Soon after this post I test the alternator and battery myself to see that they worked fine. Then I brought my Pathfinder to two different AutoZones. One said my battery and alternator were low then the other one said both were fine. I thought about changing the alternator anyways, but then just decided to disable my horns. This was for about three months now.

A few nights ago I was driving home from school when my Battery and Brake light when on at the same exact time. I brought it to a Nissan dealership this time. I told them about all my alarm and windshield wiper problems, but the service representative only seemed to care about why the lights were on, which was frustrating. The next day he calls and tells me my alternator was indeed messed up. I get my car back today hoping that the new alternator would solve my problems but it has not. As I was driving home my windshield wipers went on. As I was doing the dishes my car alarm went off three times in 5 minutes…

I jump back into car fixing mode and search the service repair manuals for more answers and I have so many ideas that I don’t know where to start.

1.	How can I disable the alarm system all together?
2.	How can I test/check my door switches (I realized I cannot physically lock my doors while using the key, is this normal?)
3.	Should I use my multi-reader to try and test the fuse housing?
4.	Would a shop that deals with alarms be able to help me more?
5.	What electrical components (fuses and controls) operate the alarm? I had a power control module burn out on me a year and a half ago right before this all started and I’m wondering if anything replaceable alarm component may have burned out too.
6.	Any further suggestions?

I really enjoy my car, its my first car since I was 16 (im 23 now) and everyone says it’s in great shape (save for needing a timing belt now) I’m still in college and won’t be able to afford a new car. I was always hoping this car would last me till I found a solid job/career, but lately I keep thinking about getting a new car and living in debt trying to pay off a new one.

Thanks for all your help everyone.


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## IanH (Feb 11, 2003)

I will have to find an FSM for your car before i can help, maybe tomorrow i can reply


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## IanH (Feb 11, 2003)

Both alt and brake light on together is the Alternator, this is what happened on daughters SE-R, and others have reported this. the service writer should have known this.
Reading this through again i think you could have some damaged wiring the goes to the wiper and Alarm system.
Who and what was done to the car when this started happening ? 
It seems like you are saying the people who worked on the car and replaced the PCM relay.
Check the wiring around this part. look for wiring caught under brackets or damaged/cut insulation, rubbing on metal etc.
There are however other possibilities for both as separate problems.

Please explain what the PCM relay does and where it is located.


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## IanH (Feb 11, 2003)

did you check this out ...from above from "thecrow163"

Just a thought about the alarm going off by itself. I know for sure that you cannot lock your doors with the remote only when one of them is ajar. This means that the little switch that the door presses on when it closes is not functioning correctly (or it's rubber housing has deteriorated). This would explain the alarm going on by itself and your not being able to lock the doors using the remote. Check if the cabin light is on when this happens, it will definitely confirm this.
Check all the switches of the doors and hatch.
Hope this helps.

The wiper coming on by themselves could be the park switch going out of adjustment in the unit.


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## IanH (Feb 11, 2003)

re- security system
what does your red light do...
when a door is open, how often does the light blink, time between flashes, time for 10 flashes you choose.
shut all door and tailgate, is light on continuously, after about 30 - 40 seconds, how often does the light blink
did you download the FSM?, get the 97 pathfinder FSM from Phatg20.net and look at page number EL-215


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## IanH (Feb 11, 2003)

you can isolate where this false signal is coming from by dis-connecting the activation wires one at a time from terminal 15, 16, 26, 29 on the "Smart Entrance control unit."


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## HalfJoey (Jun 29, 2008)

Wow, thanks a lot for your replies. Sorry I haven’t gotten back to you in a few days. I will attempt to absorb and answer you very good questions and suggestions.

1. This started happening to my car when my car’s engine would just turn off while it was idling. No one could find the problem till one shop saw my PCM relay was burned out. I guess the PCM relay regulates power throughout the engine. The shop replaced it and immediacy after this my windshield wipers started going off on their own. I took it back to the shop and they couldn’t find the problem but suggested a $300 repair that “might” fix it… I didn’t take their repair. I will try and locate my PCM power relay. And I’ll look around under my car’s hood for wiring issues.

2. Ok I just ran some tests on my alarm lamp indicator. 
a. When I open the driver side door the security light flashes (10 flashes in 10 seconds)
b. When I close the door without arming the alarm there is no light
c. When I arm the alarm it takes 25ish seconds for it to start blinking.
d. When it starts to blink It takes 20 seconds to reach 10 blinks.
e. When I press the disarm on the remote there is no light.​
I Downloaded the FSM and while looking at page El-215 It seems that everything is normal with the timing of my security lamp blinks.

3.Do you have any suggestions about how I can test the connections in my door or which doors its coming from?

4. Where can I find the park switch in windshield wipers? I think I see where the windshield wiper motor and the wiper amp is located, but its closed off, should I try to open that and see what’s up? Should I have my car running while I do this to see if moving wiring affects the wipers?

5. I see in the FSM were to locate the “Smart Entrance Control Unit”, but is it easy to get to? Should I disconnect the battery before doing anything? How should I go about testing this? Disconnect one terminal and see if my alarm goes off? If one does solve the problem does that mean there is a bad wire along that path?

6. How can I just shut off my alarm completely? There is a cord I can unplug to deactivate the alarm all together? I tried just closing my door when manually locking it, but the alarm still goes off then.


Thanks so much for all you help. I really feel like I’m getting close to a solution here. I work best when I can break things down to how they work.


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## IanH (Feb 11, 2003)

HalfJoey said:


> 3.Do you have any suggestions about how I can test the connections in my door or which doors its coming from?
> 
> 4. Where can I find the park switch in windshield wipers? I think I see where the windshield wiper motor and the wiper amp is located, but its closed off, should I try to open that and see what’s up? Should I have my car running while I do this to see if moving wiring affects the wipers?
> 
> ...


3. not really, you can isolate the doors from the module...don't know what this would entail, or disconnect where the wiring goes to the door switches. 

4. this is in the motor housing, check the wiper arms can return all the way to a normal parked position. If its really this you can nudge the arm with something, and it will do one wipe cycle. Easiest would be a used unit from a wrecker.

5. disconnecting the battery when working with any modules or solid state electronics is a good idea. however if this its turned off when the ignition is off that's good enough, check the wiring diagram.

6. will have to study the wiring diagram, but removing the sense wires should make it blind...


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