PO48 Current/ EGR Fault

10328 Views 36 Replies 10 Participants Last post by blue90sdv, Sep 4, 2009

MrSeville4.9

Discussion Starter · Sep 19, 2008

My service engine light is on and i have the current po48 which is the egr fault. The car seems louder than normal. There is a very slight loss of power in acceleration. What exactly could be the egr fault? The egr diaphram seems to move up and down... I dont know... ANyone...Help!!!

1 - 20 of 37 Posts

noahsdad

· #2 · Sep 20, 2008

The symptoms you describe point to a torn diaphragm in the EGR valve. Because the EGR is exhaust gas recirculation, the additional noise is from the exhaust that normally pumps through the valve. The spongy acceleration is from a loss of vacuum.

Not a difficult fix, well within the means of an average DIY.

HUF

· #3 · Sep 20, 2008

First thing (and likely the only thing) to do is cleaning two EGR tubes inside the throttle body under the blades with coat hanger. Do not be afraid of chunks of carbom falling down. It is also a good time to clean the bores and back sides of the blades with a tooth brush and carb cleaner. My 048 code and SES light went off after I performed that cleaning 8 years ago and never were back.

MrSeville4.9

Discussion Starter · #4 · Sep 20, 2008

Thanks Fellaz... I'll try these solutions. NoahsDad, what is a DIY?

HUF

· #5 · Sep 21, 2008

DIY = Do It Yourself

MrSeville4.9

Discussion Starter · #6 · Oct 10, 2008

Thanx...LOL

Sevillian273

· #7 · Oct 12, 2008

Ive never had the E048 code before, but I did remove the EGR valve and installed a block off plate in its place to troubleshoot the cause of a miss/stumble. I meant it to be temporary but the plate has been on there for nearly 1000 miles and I havent noticed any change at all. No detonation, no change in mpg, and no egr code. My base timing is at 14 degrees and I run 93 octane. The solenoid is still plugged in but the valve is on a shelf in my garage. I DO NOT recommend anyone try this as it goes against everything Ive read here. It was only an experiment but since Ive seen no change at all from it, I havent gotten around to putting it back on.

Based on what Ive experienced, I dont think the valve itself can set the code unless the ECM infers that there is an issue based on readings from other sensors. My guess is that the code sets when the solenoid malfunctions because it is the only part of the EGR system that connects to the ECM. Maybe I'll disconnect the solenoid and see if I get the code. Anyhoo... Just my two cents.

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MrSeville4.9

Discussion Starter · #8 · Oct 12, 2008

People... I still have the PO48 egr fault. I did not have a torn diaphram on the egr. I cleaned out the two valves under the throttle body and they were dirrrrrty. I cleared my codes. The SES came back on and my gas milage is all the way down and still droppin. Any other ideas, anyone?

HUF

· #9 · Oct 12, 2008

There are also EGR passages inside of the engine. You might want to blow some shop air through them when the EGR valve is out.

Sevillian273

· #10 · Oct 12, 2008

Detach the EGR solenoid and apply 12v to one of the pins on the unit and ground the other. Listen for a click. Then switch them and listen for a click. If you hear nothing, the solenoid is bad. If its bad, it make be stuck on open or stuck on shut or in between. It sounds to me that it is holding the valve open which means its letting some vacuum through when its not supposed to. Get a new one its about 40 bucks. If you swap it out and nothing changes then return it. I dont know what else would cause the code to set. Oh and if you can, attack the egr valve to a vacuum pump or to a vacuum line on another car to verify its operation and that it doesnt leak.

Sevillian273

· #11 · Oct 12, 2008

To check the passages, remove the valve and shove the end of a shopvac in your tailpipe(engine off of course! Lol picture that!) You should have suction at one of the holes where the valve was. Then prop the throttle blades open, put the end of the vac on the other hole where the valve was and verify suction at the egr tubes inside the manifold. This would be a good time to shove a coat hanger in them while the vac is running. It will suck the crap thru the manifold into the vacuum. BUT BE CAREFUL! If you bend the tubes out of their pressed-fit holes you will never get them back in again. They appear to be made of brass so if they fall inside out of sight, you wont be able to get them out with a magnet.

cadillac_al

· #12 · Oct 13, 2008

It could be a clogged catalytic converter; especially since you said it's louder than normal. My old 87 Ninety Eight gave me an EGR code so I replaced the EGR valve and it turned out to be the cat. I learned then that an EGR code doesn't necessarily mean bad EGR valve. It's the EGR system that is malfunctioning. If you check the vacuum a bad cat will give you a very low reading I believe ( or was it a very high reading, I always forget). Good luck.

HUF

· #13 · Oct 13, 2008

cadillac_al said:
It could be a clogged catalytic converter; especially since you said it's louder than normal. My old 87 Ninety Eight gave me an EGR code so I replaced the EGR valve and it turned out to be the cat. I learned then that an EGR code doesn't necessarily mean bad EGR valve. It's the EGR system that is malfunctioning. If you check the vacuum a bad cat will give you a very low reading I believe ( or was it a very high reading, I always forget). Good luck.

Good point. The EGR valve operation has something to do with backpressure. Wrong backpressure might affect EGR valve and set a code.

noahsdad

· #14 · Oct 14, 2008

While a plugged cat could be causing some of the rough running issues, the Cadillac 4.x series engine uses a negative backpressure EGR valve, which isn't affected by increased exhaust backpressure (Conversely, the previous poster's Olds 98 has a positive pressure EGR, which could be adversely affected).

Mr.Seville, have you checked to see if the EGR is functioning? Start the engine and let it warm up, place your fingers under the diaphragm and increase the RPMs to about 2000. You should feel the diaphragm move under vacuum pressure.

If it doesn't move, check the vacuum hoses carefully running to the EGR solenoid, and to the EGR valve itself. Remove the valve and check the passages in the manifold and the valve, they may be plugged. The solenoids rarely fail, but if the valve works with 7 pounds of vacuum applied to it, that's the next place to look.

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Sevillian273

· #15 · Oct 14, 2008

What other way can the ECM see the EGR system other than the solenoid? My solenoid is new and its still plugged in but Ive got a block off plate in place of the valve and I dont get any codes. My car runs fine with zero EGR. I think his solenoid is stuck open at least somewhat which is holding the valve open just enough to make it run rough but not stall. I think the stuck solenoid is drawing too much current which is setting the code. Thats my best guess.

noahsdad

· #16 · Oct 14, 2008

The ECM controls the solenoid, but doesn't accept any data from it. The E48 code is set by the oxygen sensor, which produces a predictable cycle of lean conditions when the EGR is functioning normally.

Sevillian273 - You can plate off the EGR and run fine, but if you live in a state with mandatory emissions inspections, your car will fail due to high NOX.

Sevillian273

· #17 · Oct 15, 2008

Ohh I gotcha. So I wonder if my ecm will ever notice my lack of egr.... Its been nearly 1000 miles without it. Theres no smog testing here in FL so I dont have to worry about the law poking around under my hood:shhh:

MrSeville4.9

Discussion Starter · #18 · Oct 21, 2008

Everyone... I still have the PO48 code. There is a few things that i do need to check that I've learned from all the postings. But... One piece of info I forgot to mention is that I cut my Cat out bc it went bad and i didnt need to replace it bc i dnot have to take emissions. So w/o the backpressure from the Cat, is this affecting my whole emissions system? There were a few postings about this from cadillac al, noahsdad, and HUF.... WHat do you guys think?

HUF

· #19 · Oct 22, 2008

MrSeville4.9 said:
Everyone... I still have the PO48 code. There is a few things that i do need to check that I've learned from all the postings. But... One piece of info I forgot to mention is that I cut my Cat out bc it went bad and i didnt need to replace it bc i dnot have to take emissions. So w/o the backpressure from the Cat, is this affecting my whole emissions system? There were a few postings about this from cadillac al, noahsdad, and HUF.... WHat do you guys think?

No. it should not set E048 code. Many others had to cut the cat converter off and nobody reported such a code as a result.

RexCaroll

· #20 · Oct 31, 2008

"The E48 code is set by the oxygen sensor, which produces a predictable cycle of lean conditions when the EGR is functioning normally.":

Im getting a e048 code now also.

I posted before my car is running rough at low rpm. Would a clogged fuel injector cause the motor to run lean and give a 48 code then as well?

My car was parked for 6 years and the gas went bad in it. Im thinking the injectors might be plugged (one or two anyways)

Rex

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