pmlong1028@gmail.com Report post Posted January 17, 2018 Allison 3000 displays check transmission light occasionally within a couple minutes of startup. Allison dealer read code as one inactive high voltage fault. Replaced alternator but still get an occasional check transmission momentary light. Is there anything else that could cause high voltage fault. I have owned the 2014 American Tradition for three years and this problem started a couple of months ago. Thanks Patrick Long Share this post Link to post Share on other sites
bm02tj Report post Posted January 17, 2018 Maybe the alternator was not at fault-- was it tested? Is it built in regulator or remote regulator? Share this post Link to post Share on other sites
wolfe10 Report post Posted January 17, 2018 Patrick, Welcome to the FMCA Forum. Have you re-checked for diagnostic codes (easy from the shift pad-- no equipment needed)? Same code? Safest power source for the Allison is to run two (one for memory and one for operation of the Allison ECU) directly from the battery with a fuse at the battery. The more things on the same circuit as the Allison ECU, the more chances that something will cause a spike (more likely than just high voltage unless your dash voltmeter did indeed show over 14.5 VDC). Share this post Link to post Share on other sites
pmlong1028@gmail.com Report post Posted January 17, 2018 Dash voltmeter showed 15.9 prior to replacing alternator. Alternator has internal voltage regulator. Have not checked for possible code after most recent incident but it was so quick I doubt it registered. Share this post Link to post Share on other sites
wolfe10 Report post Posted January 17, 2018 The code will register if you have an overvoltage issue. What is voltage reading at the dash with the new alternator? And, totally agree, 15.9 is WAY too high. Share this post Link to post Share on other sites
pmlong1028@gmail.com Report post Posted January 17, 2018 Dash voltmeter showed 15.9 prior to replacing alternator. Alternator has internal voltage regulator. Have not checked for possible code after most recent incident but it was so quick I doubt it registered. Voltage reading at dash with new alternator 13.9. Current fault P 0883 ( TCM Power Input Signal High ). Voltage spiked briefly to 16 today after coach was running for 3 minutes. As you suggest, something other than alternator is probably causing problem, plan to have Freightliner look at it and will let you know what they find. Thanks Patrick Share this post Link to post Share on other sites
jleamont Report post Posted January 17, 2018 Patrick, I have had several Delco alternators on Freightliner trucks do the same thing as you experienced, it could be a defective alternator, assuming that is what its equipped with. One recently at 18V Allison went into Limp mode and wouldn't shift. That alternator was only 8 months old from the last over voltage problem. The Freightliner dealer should be able to fix you up. Delco QC has drastically dropped off in the last few years in general, starters not lasting 1/2 as long as before also. Share this post Link to post Share on other sites
wolfe10 Report post Posted January 17, 2018 If you have an alternator with an external SENSE WIRE, could be nothing more than a corroded or poor connection at that small gauge sense wire at either alternator or other end. If sense terminal of alternator receives a low reading (even artificially low due to bad connections)it will make the alternator put out excessively high voltage to compensate. So, check to see if your alternator has an external sense wire and check that first. And, yes, a loose connection could easily go from correct to erroneous reading as you drive. Share this post Link to post Share on other sites
