EGR system, Code 33

J

justin07

Registered
I'm getting an intermittent c/e light on the highway. i pulled the codes and i'm gettin #33 which has to do with the egr system. i took the egr valve off and tested it with a vacuum pump and it opens and closes fine, i replaced the DPFE sensor and cleared the codes, but i'm still getting a c/e light on the highway and code 33 is still coming up. Does anyone have any ideas on what the problem could be from this point?
thanks,

Justin
 
RE: EGR system, Code 33

It may still be the EGR valve, as the operation is dependent on the amount of vacuum and a vacuum pump could move a valve that would be sticking under normal conditions.

Regards,
Andy
 
RE: EGR system, Code 33

Code 33 is defined as "PCM did not detect EGR opening when commanded". There's a few possibilities besides the valve or PFE.

When the PCM commands EGR, it sends a ground to the EVR (EGR vacuum regulator) mounted on the bracket on the left rocker cover. This opens, allowing regulated manifold vacuum to apply the EGR. If no vacuum makes it there, the valve cannot open. Check the green line back to the EVR. Is it cracked and leaking or crushed and blocked? At the EVR, remove the double vacuum fitting, start the engine and check for full manifold vacuum at the other line. If it's not there, follow that line back to the intake. Leaking or obstructed?

On a few very rare occasions, I've seen 4.6s with the EGR tube or internal EGR passage in the intake plugged with carbon, but that's easy to test. Let the engine settle to base idle and use your vacuum pump to force the EGR valve open. By about 10"hg the engine should get noticeably rough or stall. If it doesn't, exhaust gas can't get from the exhaust manifold to the intake.

It could be wiring, but check these first.
 
RE: EGR system, Code 33

I finally got around to checking this stuff out on the car, it's been raining alot lately. i checked the line goin to the evr and vacuum is present. I applied vacuum to the green line that goes to the egr valve while the car was running and the engine began to run very rough, so i know the line to the valve is fine and the passages arent blocked but i knew that already cuz i cleaned them out when i took the valve off a while ago.
How can i test if the EVR is outputing vacuum to activate the valve? i need to get a new evr anyway one of the vacuum nipples broke when i was taking the the lines off. but i'd still like to know how to test it for future reference.
we'll see if the new evr fixes the problem, thanks,

Justin
 
RE: EGR system, Code 33

All EEC actuators work the same way: there's a constant 12v supplied to them with the key on and the PCM functions them by providing ground.

Your EVR has 2 wires going into it. The red should be live, and the other wire is the ground (signal). You could have tested the EVR by simply providing your own ground with a jumper wire into that pin. The EVR would slam wide open, the EGR would get full manifold vacuum, and the car would stall (assuming all the lines and passages are OK).

If all of this is good, we're left with one last question. Is the PCM capable of turning on the EVR? This gets tricky, because the conditions the PCM wants to see to command EGR opening are pretty well impossible to duplicate standing still. We could check continuity of that ground wire from PCM to EVR, and if it's good, condemn the PCM by process of elimination. I won't do that. Any tech with a decent scan tool should be able to perform what's called a "Function Test" or "Command Test" which will basically trick the PCM into opening the EGR at idle. If it's unplugged and a vacuum gauge is in that green line, our question is answered.

This will make you feel better: I don't think I've ever replaced a PCM for an EGR command problem. If the new EVR doesn't fix it, follow the signal wire back as far as you can or try some resistance tests.

Good luck, Justin.
 
RE: EGR system, Code 33

I have one other thing for anybody reading these posts. Justin, I'm assuming you checked this when you went through the aggravation of replacing the DPFE. The PFE must be capable of reading changes in backpressure within the EGR tube. The small silicone tubes going to the sensor must not be leaking or blocked. If they need to be replaced, DO NOT use conventional vacuum or fuel line. Exhaust gases (and all heat that entails) flow through them. Rubber line will last about 10 minutes and when it melts, bits will go inside the PFE and destroy it!

Here's how the (D)PFE works: When the EGR valve is closed, backpressure builds up within the tube between the valve and exhaust manifold. When the PCM commands the valve to open (using the EVR) it needs some form of information feedback to see if its command was obeyed. As the valve opens, pressure inside that tube will drop. If the command is for a large enough opening, there may even be a small amount of intake vacuum in there. The PFE reads these changes and can provide the PCM with very accurate information about when and how much the EGR valve actually opened. That's how we can get codes like, "PCM did not detect EGR opening when commanded".

Hope this clarifies things.
 
RE: EGR system, Code 33

The EVR did the trick,.. i changed it and everything is good now, no more CE light. thanks for all the info and help!

Justin
 
RE: EGR system, Code 33

Great! I didn't expect that you would have to go much further than that. Just tried to cover all the possibilities.
 
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