Is the EGR suction test foolproof? CEL P0402

[BuffaloXplorer]

I've got an intermittent CEL code P0402 (Egr Flow Excessive) that occurs ONLY AT IDLE.

For those with advanced knowledge of the emission control systems, according to my CarChip, the CEL occurs anywhere between 750 & 900 rpms (usually at a stoplight or shortly after startup) and I've never had it occur at a time where i was accelerating or cruising. Not sure if this is an indication of anything specific, but i figured all info may help the over-the-net diagnosis.

I've replaced the DPFE & Solonoid already. I've tested the EGR by applying suction to the vac port and it affected the idle (engine lopes) the way it should (?).

Is this a foolproof test for the valve? If not, is there another test that IS before i spend more $$$$ on a valve that may not be the problem (and not to mention a b!tch to replace)? I've searched and read that a dirty TB may be a factor, but highly doubt it could be a free fix .

I had this same code occur 2 years ago and the mechanic changed the DPFE, which was the problem.

 

[joemamaugly]

hey chris where in buffalo are you? i see the tops and the houses and wonder if you're not in the grant and amherst st area. just a question i'm in buffalo too.

 

[BuffaloXplorer]

****, i thought i actually had someone who knew the answer to my Q...and it turns out to be a local...

i'm actually a block from Tops on Niagara - downtown buffalo. Where u from...?

 

[Glacier991]

Actually that result (the scanner result) more than ever points at the EGR. While I realize the vacuum test suggests otherwise, it only tells you the diaphragm is intact... metering or other things could be at fault. AM I sure? no. I don't like the "not sure, buy and replace" method of auto repair, but in your case *I* would pop for the EGR valve replacement, were I you.

Oh and, have I ever replaced an EGR valve unnecessarily? yep. Factor that in.

But remember a crudded up valve WILL flow at idle. A no no. Even if the diaphragm works perfectly, if the valve is crudded up, it may never close fully.

 

[BuffaloXplorer]

thanks for all your help, glacier...

Well, i guess i'll be getting the egr taken care of sooner rather than later.

On a side note, according to carchip my TPS indicates 18.82% open at idle...i'm guessing that it's never actually closed (0%) but 20% open at all times sounds high. What do you think? I plan on checking the voltage at the sensor this weekend.

 

[BuffaloXplorer]

***even though it reads almost 20% open, my idle runs between 750 & 850 rpm

 

[Glacier991]

check the TPS voltages... ideal is .96v at idle, and should go up to around 4.0 v at full throttle. If you are worried this is the problem, you can unhook the sensor and have the computer substitute tabular values.... in effect "inventing" numbers that work. This WILL throw a code, be advised, you'll have to clear it... but it's not a bad way to see if the part is bad. (This does not work for ALL sensors).

 

[BuffaloXplorer]

Thanks, i will try unhooking the sensor. However, if i unplug the sensor, my carchip will no longer receive data about the throttle position, right? Or is the data derived elsewhere in the system? I guess i can just unplug the sensor and then check the program tonight to see if it receives data regarding throttle position..