QuestionQUESTION: Battery wont charge despite new alternator. Checked battery, cables and replaced alternator. Battery still wont charge and light is still on. Any ideas??
ANSWER: Hi Bob,
It could be the powertrain control module (engine computer) is not properly energizing the field coils of the alternator. Could the belt be slipping on the alternator pulley? Could you have a short circuit that is drawing down the voltage of the system? You didn't state the year/make/model/engine so I can't tell you specifics. But try get a fault code readout to see if any code pertains to the charging circuit. Pre-'96 are OBD-I and the ignition key can be used; '96-on are OBD-II and you read it with a plug-in code reader that plugs into a socket under the dash. Autozone will do that readout for free at most stores. Then let me know all the details and we can go from there.
Roland
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QUESTION: Wow thanks for the quick response. It is a 96 LXI convertible. 6 cyl. The belt does make some noise but it doesn't seem to be slipping. So the code should tell me?
ANSWER: Hi Bob,
Yes, the code will give you a hint. There is a good chance that you can use the ignition key:"on-off-on-off-on and leave on" doing that in 5 seconds or less elapsed time. Then watch the check engine light, that remains 'on', to begin to flash, pause, flash, etc. Count the number of flashes before each pause. Then repeat to be sure of an accurate set of counts. Group the counts in pairs in the order of appearance to form the two-digit fault code numbers. Then write back or go to www.allpar.com/fix/codes.html for a code list.
Roland
PS I'll be available for a question at the top of the hour, so let me know then what codes you got.
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QUESTION: Once again thanks for the quick reply. Here are the codes I received and double checked.
12 41 66 31 55
Multiple codes...ouch
AnswerPS: You can also get that OBD-II readout which would give you a confirmation of the need for a new PCM or not. Autozone parts stores will often do it for free. Please let me know if there is some ambiguity about the meaning of the codes.
Hi Bob,
The relavent code is 41 which says that the field coils are not being controlled properly at the alternator. You could check that the dark green wire from the alternator to the pin 4 of the 40-pin plug at the PCM is patent and not shorted to ground (remove both plugs (at the generator and the pcm to test the wire). If it appears OK then the code 66 may be the key here because it points to a possible failure of the PCM itself. You might find a used PCM for the same year/model to replace the old one.
The 31 says there is a leak in the fuel vapor recovery system, the 12 says the battery was disconnected recently(when the alternatore was changed, no doubt) and the 55 says 'end of readout'.
So check that dark green wire and if that is ok I would look into finding a replacement pcm at a wrecking yard or via their 'nationwide hot line' to a number of other such yards.
Roland
