Nissan Murano Forum banner
1 - 14 of 14 Posts

· Registered
Joined
·
5 Posts
Discussion Starter · #1 ·
When I start the car it shows between 11.7 and 12 volts from the charging system. Once it warms up ( I let it idle for about 10 minutes) suddenly starts charging 13.6 to 14.1 volts. Once it's warm can turn off the car and restart no charging problem, but if you let it cool down goes through the same warm up thing and then starts charging again. I tested the ipdm with the on board test and everything seems fine. Could this be the pcm?
 

· Registered
Joined
·
3,590 Posts
How many miles?

If you are only seeing 11.7 - 12 volts initially, you may have a bad battery... The battery alone if it's healthy should be around 12.3 - 12.67 volts.

Have both tested. Also make sure the battery terminals are totally free of corrosion and snug, and check the negative battery terminal cable grounds under the battery and at the CVT. Replace the cable if there has been a history of severe battery terminal corrosion.
 

· Registered
Joined
·
5 Posts
Discussion Starter · #3 · (Edited)
144k .Checked the battery alone this morning, it is at 12.1 volts in the cold (40 degrees this morning). I didnt see any corrosion to speak of. Voltage drops while the car is running until the car warms up then it starts charging 13.6 to 14.1 volts. Makes no sense to me, I'm used to alternators stopping working when they get too warm not the other way around
 

· Registered
Joined
·
3,590 Posts
Check the serpentine belt to be sure it's in good condition and not slipping when cold.
 
  • Like
Reactions: I need coffee

· Registered
Joined
·
2,375 Posts
The procedure for checking belt tension is in the service manual (see the "Maintenance" file): https://www.nicoclub.com/nissan-service-manuals. You really need an inspection camera to do it (or an inspection mirror).

If the belt is fine then see if you can get to the alternator connectors and inspect them. In your initial post, you went right to the ECM--not sure why unless there is other evidence you have. The ECM does have primary control over the alternator duty cycle so I guess you can unplug the battery current sensor on the negative cable and see if that makes a difference (... I think doing that will throw a DTC though).
 

· Registered
Joined
·
5 Posts
Discussion Starter · #6 ·
Serpentine belt is new less than 2 months old.
The procedure for checking belt tension is in the service manual (see the "Maintenance" file): https://www.nicoclub.com/nissan-service-manuals. You really need an inspection camera to do it (or an inspection mirror).

If the belt is fine then see if you can get to the alternator connectors and inspect them. In your initial post, you went right to the ECM--not sure why unless there is other evidence you have. The ECM does have primary control over the alternator duty cycle so I guess you can unplug the battery current sensor on the negative cable and see if that makes a difference (... I think doing that will throw a DTC though).
Other than visual inspection and not seeing any corrosion or loose connections that the car just starts charging again after about 15 minutes running time I am at a loss for why it's doing this that's why I asked about the ecm. I did unplug battery current sensor and it made no change at all. Did not throw a code that I can pull on my scanner just the battery and brake light illuminating which after about 15 minutes run time will go off and the system is charging again. It's the getting warm and then charging that throws me for a loop. Even if you shut it off and restart it still charges unless the car has cooled significantly, then it's back to the same cycle
 

· Registered
Joined
·
2,375 Posts
Serpentine belt is new less than 2 months old.
How new are the tensioner and idler pulleys?

BTW, are you measuring this low voltage at the battery terminals with a DVOM or is this what you're reading on your scan tool?

If all else in the charging system checks out, you have to suspect something is going on with the voltage regulator in the alternator. It is an odd issue and I'm surprised the engine can run for 15 minutes with no alternator output after the car's been sitting overnight. Definitely post an update when you find the root cause of the problem.
 

· Registered
Joined
·
5 Posts
Discussion Starter · #12 ·
When I start the car it shows between 11.7 and 12 volts from the charging system. Once it warms up ( I let it idle for about 10 minutes) suddenly starts charging 13.6 to 14.1 volts. Once it's warm can turn off the car and restart no charging problem, but if you let it cool down goes through the same warm up thing and then starts charging again. I tested the ipdm with the on board test and everything seems fine. Could this be the pcm?
UPDATE**
The problem was the internal voltage regulator in the alternator. After the swap a friend of mine that owns a local electronics shop and I opened it up and found there was a tiny gap in the wiring that, I'm guessing, expanded when it got warm and started charging again. Granted the charging capacity was slowly going lower and probably would have stopped altogether once the wire piece had burned enough to no longer connect. Guess we can chock it up to the very strange but could happen file. Thanks for all the input about this little piece of insanity.
 
1 - 14 of 14 Posts
Top