Howdy!
I used a code reader on my truck yesterday and it came back with "exhaust gas recirculation insufficient" what does this mean?

EGR valve is probably shot or shooting craps.

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(Project Dirty Girl) 06 Chevy 3500 CCLB DRW 4WD (D-Code) LBZ Duramax - Air Box Mod, High Flow Filter, Turbo Silencer Removed and capped, LMM Sensor Pack, LML Turbocharger Solenoid, EFI Live Tuned by Myself, TranSynd for the Allison, Awaiting more mods, 100 + Injectors, PPE Hot Fueler Kit, PPE Dual Fueler kit, PPE Compound Kit and Mike's ALLY Trans Setup - Inglewood Trans!

Is it hard to change out?

What's the exact code. Could also be just the dpfe sensor depending in the code

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right, that sounds like the code that i had - insufficient flow ... dpfe sensor was returning a high signal...
i had p1401

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1999 xlt 2.5l 5-speed Supercab 159k
83 diesel 2.2l na
06 F250 6.0l psd
{click for lol}

not hard to swap out about 15-20 min you can try cleaning it out first with carb cleaner but you will prob end up having to replace it.

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94 2.3L Ranger 340,000 miles and counting

It could be one of three causes. 1) EGR valve 2) EGR regulator solenoid 3)dpfe sensor
There are ways to test them. Don't waste money replacing parts if you are not sure which one is bad.

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2001 Ford Ranger with the flare sides. 4x4 with a 4.0 engine. The only thing I did so far is: F/R Brakes, rotors, drums, F/R shocks, tires, bed cap, cone filter, hanger/shackles, F/P wheel bearing, upper control arm, lower ball joint, filler neck, fuel filter and DPFE sensor, muffler, sway bar links and spark plugs!

How would I go about testing them? ... And what happens if I just ignore it?

You can drive it, it will use more fuel than normal and it might run rough. It will shorten the life of the engine if not taken care of in the long run.
Test the EGR valve first. Locate the ERG valve, remove the vacuum hose on top. Install a vaccum pump in it's place. Start the engine. Pump the vacuum pump to about 18. The engine should start to hesitate and try to stall. If it does, the EGR valve is good. With the engine off, pump the vacuum pump to around 18 again and see if it holds for about 20 seconds. This tests the inside bladder if it's good or has a leak.
(The EGR valve opens when vacuum is present and only when in drive, it dosen't hesitate while driving because Oxygen is entering the air in take. Using the vacuum pump is a method of jumping it while in park).
You can pick up a vacuum pump at Harbor frieght for about $25. It is also used for bleeding brake lines, always good to have one in your tool box.

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2001 Ford Ranger with the flare sides. 4x4 with a 4.0 engine. The only thing I did so far is: F/R Brakes, rotors, drums, F/R shocks, tires, bed cap, cone filter, hanger/shackles, F/P wheel bearing, upper control arm, lower ball joint, filler neck, fuel filter and DPFE sensor, muffler, sway bar links and spark plugs!