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Ask GM Tech (Cam) Your Own Question
GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 15181
Experience:  GM Grand Master Technician 2007. 14 years experience.
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02 CHEVY TAHOE BATT. LIGHT IS FLASHING HAD CODE 1638 CLEARED

Customer Question

02 CHEVY TAHOE BATT. LIGHT IS FLASHING HAD CODE 1638 CLEARED AND REPLACED ALT. BATT. LIGHT STILL FLASHING
JA: Do you happen to have a code reader or scan tool? What size is your engine?
Customer: 5.3 YES HAVE SCANNER
JA: Tell me a bit more about what's going on so he can help you best.
Customer: ALT LIGHT CAME ON 3 TO 5 SECONDS GOES OFF. CHECKED VOLTAGE AND SCANNED CODES IT SHOWED P1638 .REPLACED ALT. STILL BATT. LIGHT BATT. LIGHT FLASHING
JA: Are you hoping to fix this yourself?
Customer: YES WHY?
JA: Great! What have you tried so far? Is there anything else the Chevy Mechanic should be aware of about your Chevy?
Customer: NO
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the Chevy Mechanic about your situation and then connect you two.
Submitted: 9 months ago.
Category: Chevy
Expert:  C. Walker, Jr. replied 9 months ago.

Supply 12v through a test light on the Brown wire at the alternator, check for charge. Test voltage drop on the alternator B+ circuit, engine running, alternator charging. Should have less than 400 millivolts. Test voltage drop on the alternator B- circuit, engine running, alternator charging. Should have less than 50 millivolts.