alright, this is more for my dad and his 6.2. his glow plug light, from what he told me, intermittently turns on and off even if his engine is warmed up. is there a problem? maybe a bad relay or a bad plug? he says it starts up fine. we're both curious as to what it is. any help would be great. and thanks in advance!

most likly the temperature switch is bad or something wrong with it on the growplug controller. it turns the glowplugs off after it reaches a certain temperature. also keeps them from turning on when the engine is hot when youre starting.

I heard a guy replaced a perfectly good glow plug controller because of this symptom when what he really had was dirt (oil grease soot corrosion ?) in the connector between the controller and the harness...

It's possible someone has bypassed the thermal inhibit switch to help with "warm" starts. The inhibit switch is there to prevent the glo-plugs from coming on after the engine reaches operating temperature. Many early 6.2's, as they get older and get miles on them, won't start when warm without the glo-plugs because of compression loss, due to normal engine wear.

The "quick fix" was to bypass the inhibit switch, allowing the glo-plugs to come on even after the engine warmed up. My truck is wired this way and has created no problems in all the years I've had it. The thermal controller keep the glo-plugs from operating when the engine is hot but they do come on when it is only "warm". After shutting off the truck when hot, the glo-plugs will come on within about 10 minutes. If I start it before that, they don't operate and the engine starts fine. After about 30 minutes, I need them, because of the above-described engine wear.

This idea for an inhibit switch came after early glo-plug failure, due to excessive heating when they really weren't needed. GM designed the thermal controller to "shut them off" when fully up to operating temp. That caused them to come on as soon as the temps dropped off, even when the engine was still warm. They issued a bulletin covering the installation of an "inhibit switch" to fix it. The next model run came with the inhibit switch installed from the factory. All worked well until the miles rolled up. Then the "No start, Warm" problem came up. Again, the quick fix was, bypass the inhibit switch. Hope this helps.

thanks everyone! i have no way of doing anything right now bc my dads truck is currently in the shop getting his windows fixed. ill let him know about all this and we'll start workin on it. thanks for the help yall!