2000 Focus. The battary light stays lit. The battary tests good. New alternator installed and checks good. CEL randomly comes on and goes off. Does not set any code, pending code or freeze frame data. All indications point to no problem with charging system. Except for the battary light which was on before and after changing alternator. Any ideas?
The last charging problem I had was on my 97 Explorer & a quick look at the charge circuit wiring diagram told me which fuses & links to check.
Sure enough the fuse labeled (strangely enough) “generator/voltage regulator” was blown & the replacement fuse did not blow.
Take a quick look at the Focus charge circuit wiring diagram.
Check the ‘L’ (lamp) lead of the alternator while the trouble is occuring. There should be 12 volts coming from the ignition area if things are ok there. It sounds like there may be a bad connection in that area. Perhaps a intermittent ignition switch connection.
So what are the voltage readings at the battery, both with the engine off and with it running?
I’ll assume this wiring diagram is correct for your 2000 Focus: http://www.autozone.com/autozone/repairinfo/repairguide/repairGuideContent.jsp?chapterTitle=Charging+System++2000&partName=Wiring+Diagrams&pageId=0900c152801ec5ac&partId=0900c152801ebfd8 A signal goes from the alternator to the engine computer (ECM). On another wire, a control signal goes from the ECM to the alternator.
To check out the alternator circuitry, you need the repair manual which has the troubleshooting charts. You need to know what is going on between the ECM and the alternator. For instance, the ECM may be seeing an electrical load that the alternator doesn’t seem to be meeting in its output. The ECM’s assumption may be wrong.
You can get repair manuals online (though, not free), from alldata.com, Mitchel.com, etc. which will have the troubleshooting for the charging system. Or, you could pay someone…
Follow up: Since we don’t see follow up’s enough on this board, I won’t be part of that “doesn’t follow up” crowd. I troubleshot the “battery always on” light on this Focus. Turns out there was a broken blue wire coming off the alternator going to the PCM. Here’s the fun part: The main engine wiring harness runs along the firewall, in the aft most part of the engine compartment. Coming off from that main harness covered with plastic loom and electrical tape are several more harness, one of them about a 10 inch harness that goes to the alternator. It too is covered with a loom and wrapped with elecrical tape. This blue wire was broken about 15 inches from the alternator plug, so 5 inches up into the main harness, past where it turns to come out of the main bundle and head towards the alternator. It was obvious that I was the first one to open up this harness. All I can figure out is that the wire must have been damaged during build up or assembly, and was holding on for dear life by a couple strands. It finally gave up after (130K miles) and there was evidence where it had been making and breaking contact for ???long. I spliced in another wire and batta-bing, it started working as advertised. So thank you hellokit, ok4450, cougar and 87 ranger for responding with possible solutions.
Nice job on the fix & thanks for the update. Glad you got it figured out.