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A. Penland
A. Penland, Ford Senior Master Technician, ASE
Category: Mercury
Satisfied Customers: 6212
Experience:  ASE Master Certified. ASE Gasoline Engine Performance Certified,Ford Senior Master Technician
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Mercury Grand Marquis: 2004 mercury battery light will not

Customer Question

2004 mercury battery light will not go out
Submitted: 1 year ago.
Category: Mercury
Expert:  A. Penland replied 1 year ago.
Hello and thanks for using JustAnswer.I will try my best to help you with your question.
What is the voltage at the battery and also at the alternator where the battery cable connects when the engine is running?
Customer: replied 1 year ago.
13,3 volts
Expert:  A. Penland replied 1 year ago.
That is a little low. It should be at least 14 volts or more.
The PCM (Engine Computer) controls the alternator output. You should first check for any trouble codes in the PCM. If there are no trouble codes, please let me know.
It will direct us to where to look for the problem.
Customer: replied 1 year ago.
We replaced the PCM
Expert:  A. Penland replied 1 year ago.
Did you have the same problem before you replaced the PCM?
Customer: replied 1 year ago.
Yes
Expert:  A. Penland replied 1 year ago.
Ok. Where did you get the alternator? Auto parts store or Ford dealership parts department.
Customer: replied 1 year ago.
Both Matthieu ford and oreillys
Expert:  A. Penland replied 1 year ago.
Ok. Check fuse #6, a 15 amp fuse, in the engine bay fuse box. Make sure it is good. Then turn the key to on and disconnect the electrical connector to the alternator and check for power on YELLOW/WHITE striped wire. It should be 12 volts.
Customer: replied 1 year ago.
Did that has 12 volts
Expert:  A. Penland replied 1 year ago.
And you are getting 13.3 volts at the battery and also at the alternator battery post?

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