2.5L ('98-'01) cel and other problems

[alt97million]

i have a 98 b2500 and i replaced the gauge cluster lights and when i did the cel and the airbag light stay on. The airbag light is code 27 to replace the bulb for the passenger part and cel codes are p1401 and p1506. these can both be cause by vacuum leaks but i dont hear any hissing and for the most part the truck idles fine. since i got the truck it has idled at about 1200-1500rpm with a small hesitation not much at all. this is to high apparently it should be about 750rpm for a manual trans. sometimes itll dip down to 500rpm and itll sound rough and ill have to tap the gas to get it to idle right again. ive tried testing the iacv and when i unplug it the rpms dont drop and it actually run smoother no more hesitation. i only let it idle in my drive may for like 5 minutes i didnt actually drive it. so im pretty sure its the iacv and not a vacuum leak. the p1506 code i dont know how to test. i have looked up symptoms of a bad dpfe and i have almost all of the first results on google bad fuel economy, it feels sluggish and cel. i dont know if rough idling and slight hesitation is from the iacv or dpfe though. what can i do now to figure out these problems? also when i say i get bad gas milage its horrible i pretty much only go to work and its 4.4 mile from my house there and back 5 days a week is 44miles i think my math is correct. and i have to fill up every week i only let it get down to 1/4 tank though. but still i can watch the gas hand go down.

 

[SenorNoob]

Considering both of those codes, It sounds like the EGR valve is stuck open. Which would effectively be a massive vacuum leak at idle.

 

[Mechrick]

The p1401 code indicates high voltage on the DPFE sensor. Normally that sensor outputs about .47v if the EGR valve is commanded off (closed). Can you read data? If so, look at the DPFE sensor voltage key on engine off. High sensor voltage can be caused by a bad DPFE or a loss of ground to the DPFE.

P1506 means the PCM can't lower the idle with the IAC valve. A big vacuum leak can do this. Someone may have cranked on the idle screw as well. You can test the valve by removing it and covering the two holes in the intake with duct tape and starting the engine. If the idle speed comes down the valve is bad.

 

[alt97million]

Considering both of those codes, It sounds like the EGR valve is stuck open. Which would effectively be a massive vacuum leak at idle.

ok thank you. ill try to test the egr valve but if that causes a massive vacuum leak that would make it extremely rough at idle and probably other engine speeds right?

 

[alt97million]

The p1401 code indicates high voltage on the DPFE sensor. Normally that sensor outputs about .47v if the EGR valve is commanded off (closed). Can you read data? If so, look at the DPFE sensor voltage key on engine off. High sensor voltage can be caused by a bad DPFE or a loss of ground to the DPFE.

P1506 means the PCM can't lower the idle with the IAC valve. A big vacuum leak can do this. Someone may have cranked on the idle screw as well. You can test the valve by removing it and covering the two holes in the intake with duct tape and starting the engine. If the idle speed comes down the valve is bad.

dont know a whole lot about reading data. would i need a multimeter or scan tool to test the dpfe? i have a multimeter somewhere and i ordered a live data scan tool. so soon i will be able to.

and i will try that with the iacv tomorrow morning. thank you for your help.

 

[SenorNoob]

extremely rough at idle and probably other engine speeds right?

Not necessarily, depends on whether or not it's within the computer's ability to compensate. It would certainly raise idle. I would expect it to be less noticeable under load.

 

[alt97million]

Not necessarily, depends on whether or not it's within the computer's ability to compensate. It would certainly raise idle. I would expect it to be less noticeable under load.

so i got some things figured out the p1506 was the iac valve it was stuck and i replaced it and a small vacuum leak i did find so that code is fixed. i still have the p1401 and i have replaced the dpfe sensor anyway because it was old and probably on its way out but that did not fix it. so i tested the egr like you said and i believe its good. i got a brake bleeding kit and used the vacuum pump when the engine is off the egr holds vacuum and doesn't drop slowly over time then with the engine running i used the vacuum pump and it bogged down so i think its good.
something kinda weird the night i replaced the 2 parts i cleared the codes with my scan tool and drove the truck for like 20 mins and the cel didn't pop back on the next afternoon leaving for work the cel is back on and its only the p1401. what should i do next?