diming lights voltage drop

[lb7lbz]

hey guys, driving the 01 dmax the other night when i noticed the headlights dim for just a second then back to normal. it did this several more times so i watched the voltage gauge and sure enough it would drop. the longer they would dim the more it dropped. am i right to assume there is a short somewhere that is drawing power? are there any known trouble spots to look for?

[More Power]

Assuming the engine temperature is past the glow & intake heater glow cycles, the problem could be the alternator. If you're still running the original alt on your 2001, it might be approaching the end....

Jim

[lb7lbz]

original alt. replaced at 205000 miles truck only has 220000 on it now so it shouldnt be the alt. however i did recheck all connections around there and all were tight. my wife says it hasnt done it lately it does seem to come and go which is why i thought maybe a short like a wire rubbing against something

[DmaxMaverick]

The 2001's had an issue with this, and there was a PCM calibration to address it. When coming to a stop, the engine RPM's dropped to idle, and for a second, voltage dropped, causing the headlamps to momentarily dim. The calibration raised the PCM controlled VR to increase alternator output about .5V. I saw the before/after of this on my truck, and the calibration was an improvement. After, it happened less often, and was less profound, but was still present. I installed a headlamp harness/relay system (headlamp power fed directly from bat+), and the issue disappeared completely.

[lb7lbz]

question for dmaxmaveric, did your truck only do this at a stop? i've never seen my truck do this at a stop only while driving, mostly around 55mph for some reason

[DmaxMaverick]

Almost always during a stop. Sounds like yours is different. Mine would do it ocasionally with accessory cycling. If you have a monster audio system, or similar, it could have something to do with it. If it is doing it at 55 for no apparent reason, you have a unique issue.