My truck won't shift down into 1st gear automatically. I can select 1 and it engages 1st gear but will not shift down at all otherwise.

tiger by the tail.!! no, 2 tigers (fignots)
no transmission maker /model told.
7 engines used world wide (no country told)
and 4 transmission used. world wide

• 5-speed FPT C510 manual,no
• 6-speed FPT C635 manual, no and
• 6-speed FPT C635 dual-clutch automatic
• 5-speed FPT C510 Dualogic automated
• 6-speed Aisin AW60T-6F25 automatic

or more wiki is not perfect, best is clearly state what transmission this is, Aisin is top maker in JAPAN. and best IMO:here..
all those words and not one EOBD PCM scans to see what the electronic transmission fails, really?

starting in 2nd gear on modern tranny smacks of transmission TCM locked into LIMP-HOME mode, and you ignoring vast PCM TCM DTC errors. buy a scan tool and use it.
the tool is free, ROI(econ) of near instant if 1 hour of labor saved the tool is free,same with service manual from fiat.

check the selection rods are all tight and not worn
with manuals it is impossible to select another gear if it is still engaged in one

try pushing the knob down onto the shifter a little bit then try and shift. Sometimes if that knob is raised even a little bit it will be locked in park. Can't be 100% sure without seein it but worth a shot. Hope that helps you.

If it pulls in 1st gear and wont shift it will be a fuse or a shifting switch in the pan of the trans

Assuming the pickup is an automatic, check the transmission fluid. The #1 cause for transmission slippage is lack of Automatic Transmission Fluid.

If the pickup is a standard shift, the pin that connects the shift to the transmission has likely broken. You would still be able to shift from the inside but the gears won't engage. A bad clutch is also a possibility but you would have noticed a burning smell prior to the clutch giving out.

sounds like filter could be clogged, if it hasn't been changed in a while. you can try to replace throttle position sencer, it is like your old trans kinkenge system, only now, it is elect. it tells trans when to shift, like your speed sencer on trans doe's. both can make it act like it is.

VTM-4 LIGHT is the 4x4 option you can use when your in the auto shift gears 1 and 2. When you put the shifter in 1 or 2 gear, you can push the VTM-4 button on dash and you will engage the 4 wheel drive constently. If you switch out of 1st or 2nd gear it will disengage automatically. The VTM-4 also works in reverse gear. Hope this helps.

yes shifter box under console has shorted so computer does not know which gear you have selected it will need whole shiftergate replaced

check the governor for sticking valves drive gear worn.governor weights or springs binding.check 1-2 shift valve sticking.check the 2-4 band damage or worn band or band not engaged in anchor pin.

you need to replace clutch pack for that gear can be ordered seperately from parts store or dealer if you want to save money call peach street auto recycling at 1800-365-2341 for a warrantied used one! also might be time for change trans filter and fluid filter could be slightly clogged but I lean towards clutch pack I replace these alot on Hondas