2001 Pontiac Montana Engine light

[olderthandirt]

Ok, first of all let me thank all of you guys that post the helpful hints in this forum. I really enjoy reading them (and learning from them as well).

I have a 2001 Pontiac Montana, 3.4L V6. The Service Engine light is steadily illuminated. I had my mechanic read the code (104 inadequate EGR flow). I had the EGR valve replaced. Drove about 3 miles and it came back on. (still read code 104 inadequate EGR flow)

In looking at the old EGR, it really didn't look very bad. It had some light carbon in it.

Next suggestion was the MAPP sensor. I replaced this one myself, but I have no way of checking the codes. I was told to disconnect the battery for 10min to clear it, but this was not successful.

The van runs fine, but that darn light is very annoying plus I have no way of knowing if something else comes up. PLus I'm probably not getting the best fuel mileage in this condition.

Your suggestions are appreciated.

['97ventureowner]

Is there a place in your area that can check the codes for free, such as an Autozone ? That may be able to tell you if there are any other stored codes to help diagnose why the light is still on. They can also clear the stored codes so you can see if the light comes back on. If there are no Autozones in your area, perhaps another auto parts place might check the codes as a free service.

[olderthandirt]

Took it to the local Advance Auto. They read the code (PB0401 inadequate exhaust gas recirculation). They cleared the code.

Drove it about 4 miles and the light came back on.

[merc81]

Took me a few minutes. . .I was looking for code 104, but as you said later it is code 401. Anyway, the pcm tests the egr system during a normal drive cycle. It does this by pulsing the egr valve open which should push up the MAP at the manifold. If the pressure isn't seen by the map sensor, it sets a counter. After about 12 failures, it lights the MIL light and sets the 401 code. Three things (outside of loose wires, bad connectors etc) can cause the problem: The MAP sensor is bad, which would also cause rough, seeking idle speeds, or the egr is bad, but you replaced yours (ouch, those are NOT cheap!), or there is some gook stuck down in the intake manifold from the exhaust gases.
I've seen the junk stuck down in the manifold. You might want to remove the upper intake manifold for a good clean out at the EGR valve location. This is much easier than it sounds, you just need to remove the stuff on top first. The gasket is reuseable. Or, you can get your head back in there and peek down the holes where the egr valve mounts to inspect for blockage. What you are looking for is a pebble size chunk of black carbon that blocks the flow of exhaust gas into the manifold.
John

[olderthandirt]

Thanks guys,

At this point I've replaced BOTH the EGR and Mapp sensor... (You're right ouch they're not cheap).

I'm going to double check the electrical connections before I tackle the upper manifold. Unfortunately, the EGR bolts on the back from the back side and it's a REAL bear to get to. I actually paid a mechanic to do it instead of myself.

Incidentally, this van has approx 114,000 miles on it.

[hufhouse]

Don't know if this will help, but I had the same code on my 6 cyl Saturn and did all the same things. I replaced the EGR (for like $200!) and replaced the MAP sensor (only like $50). I still had the problem.

Then, the car started running really poorly. Came to find out that my catalytic converter was clogged up, causing exhaust to back up and choke the EGR. I never did get any codes for the catalytic converter, though.

Just something to keep in mind.

[merc81]

I don't know about the Saturn, but there's an O2 sensor before and after the converter. It would seem if the catalytic converter was plugged up to the point of causing back pressure you would see other codes, other problems. I know from experience if the converter fouls up and restricts exhaust, it feels like you have no power but the engine will idle and run at low rpm just fine. You also hear the exhaust leaking out from anywhere it can ahead of the blockage.

As for the EGR, yea its not right up front for you to get to real easy, but its a piece of cake compared to changing the spark plugs. You need to peek down in the manifold and the pipe that comes up from the exhaust for debris. If you are more comfortable paying someone to do this, then that's the way to go for you as removing the top intake manifold is going to be more work than changing the egr was. I don't think its much trouble, but I'm pretty sure you can't get at any egr blockage without taking it off.

John

[olderthandirt]

Thanks guys, I'll see what I can get done this weekend.

I've run into bigger and better (ok worse) problems. It seems that I likely also have the frequently mentioned problem with the transmission as well. High pitched whining and hard shifting, especially after it's been driven a while.

I just had the trans filter replaced about a week ago (because of the whining & hard shifts). It does not seem to have gotten any better, I'm considering a dose of seafoam trans tune and a subsequent fluid drain & fill.

What are your thoughts on this?

[hufhouse]

The Saturn actually has FOUR O2 sensors! Before and after both "pre-converters" on each manifold.

Never got a single code about the fouled MAIN converter, even with all that back pressure.

Talk about chasing the wrong problem with the EGR valve, MAP sensor, etc.