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2001 DHS P0171 P0174


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So it's been happening for a couple months now. While idling my car runs really rough, it has even died a few times. While accelerating sometimes it hesitates and then sort of lunges. While at stop lights it is very shaky sometimes and the RPMs bounce up and down a lot. The service engine light is on and when I took it in today to get the codes read the following codes came up:

P0171 System Too Lean (Bank 1)

P0174 System Too Lean (Bank 2)

P0300 Random Misfire Detected

At first I was told it was the O2 sensor and I replaced that and it made no difference. Please Help!

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So it's been happening for a couple months now. While idling my car runs really rough, it has even died a few times. While accelerating sometimes it hesitates and then sort of lunges. While at stop lights it is very shaky sometimes and the RPMs bounce up and down a lot. The service engine light is on and when I took it in today to get the codes read the following codes came up:....

It's not necessary to take the car anywhere to read the codes. Here's how to DIY;

http://www.caddyinfo.com/readingcodes.html

P0171 System Too Lean (Bank 1)

P0174 System Too Lean (Bank 2)

P0300 Random Misfire Detected

At first I was told it was the O2 sensor and I replaced that and it made no difference. Please Help!

The combination of P0171 and P0174 on your year model engine is a 100% certain indication that the rubber coupling between the throttle body and the intake manifold is cracked and allowing unmetered air into the engine. GM/Cadillac calls the rubber coupling a "plenum".

Whoever pointed you at O2 sensors has limited (or zero) experience with your year model of Northstar.

Replace the plenum and see if the P0300 returns. I'm betting it will not.

And just out of curiosity, how could you live with this condition for "a couple of months"? :D

Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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I believe your engine has a rubber intake plenum. It typically gets a leak, leaks unmetered air into the intake causing a lean condition on both banks

Check the rubber plenum between the TB and the intake for cracks especially the bottom

Let us know how it turns out

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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GMTA Jim

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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So it's been happening for a couple months now. While idling my car runs really rough, it has even died a few times. While accelerating sometimes it hesitates and then sort of lunges. While at stop lights it is very shaky sometimes and the RPMs bounce up and down a lot. The service engine light is on and when I took it in today to get the codes read the following codes came up:....

It's not necessary to take the car anywhere to read the codes. Here's how to DIY;

http://www.caddyinfo.com/readingcodes.html

P0171 System Too Lean (Bank 1)

P0174 System Too Lean (Bank 2)

P0300 Random Misfire Detected

At first I was told it was the O2 sensor and I replaced that and it made no difference. Please Help!

The combination of P0171 and P0174 on your year model engine is a 100% certain indication that the rubber coupling between the throttle body and the intake manifold is cracked and allowing unmetered air into the engine. GM/Cadillac calls the rubber coupling a "plenum".

Whoever pointed you at O2 sensors has limited (or zero) experience with your year model of Northstar.

Replace the plenum and see if the P0300 returns. I'm betting it will not.

And just out of curiosity, how could you live with this condition for "a couple of months"? :D

Lol good question. I have just been busy and not really had time to look into what the problem was. And I mean the car still works. It just doesn't always run properly.

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I have chased a random misfire forever, and hopefully yours can be fixed with replacing the plenum. I had the same codes as you way back when. I replaced the intake gaskets and plenum and lean bank codes went away. The boot was ripped on the bottom. The random misfire was an on going headache, a quick jab of the pedal would usually clear it up and it would appear again at random times. I changed plugs, O2 sensors, crank position sensors,COP springs, coil packs, throttle postion sensor,injectors, cleaned throttle bore, egr valve. After I had my radiator replaced I had it checked for exhaust in anti freeze and it failed, don't know if this was the problem all along because I never lost much fluid, but it was always the rear bank misfiring and the same bank would get codes for the O2 sensor. Anti freeze will kill o2 sensors.Don't know if that head gasket was bad causing the misfires, or the misfires caused that gasket to go. Thought I would share that with you.I hope it is the plenum has a leak.

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