Check Engine Light, EGR, Throttle Body

[rtelles]

Vehicle: Dodge Caravan
Year: 2004
Engine: 3.3L
Mileage: 55,000 km/34,500 mi

Hi everyone:

I am new to this forum but I have been reading hundrends of posts today and finally decided to make my first post since I have a couple of doubts... So here goes the story:

2 weeks ago my wife had an accident and hit another car on the side (the only things damaged on the minivan were the hood, front bumper and LH light). Since it was not my wife's fault I decided to take the minivan to the same dealer were I bought it, they charged a lot for the repair but then again the other person insurance assumed full responsability... Anyways one day after the accident the Engine Light lit, but it turned off before taking the van to the dealer. After I got the minivan back the light was still off and the mechanics said if it had not come again probably it was something minor.. 15 minutes after leaving the dealer the light came ON again but the shop was closed so I went home. I have a CARCHIP (ODBII reader) installed so I checked what was causing the Light and it was P0404 and P0405, which is basically EGR Malfunction. BTW I can reset the Engine Light with the CarChip but if I do not solve the problem it would keep just lighting up.

I printed the report and took the van to the dealer. I got a call from the mechanic 20 mins after I left the minivan and he said that to clear the Engine Light he would replace the EGR (under warranty so no cost) but that he also needed to perform a Throttle Body Service because there was a lot of carbon buildup (for this he would charge $100 + taxes that would come out of my pocket). Additionally he said that I needed a Fuel Injector Service since this is suggested by the manual every 45,000 km.

Well I refused the Fuel Injector Service (for $100) and still was in doubt about the $100 of the Throttle Body cleaning because after reading on the Internet I found out it is easy to do and would cost me $5 for the cleaner. Since I wanted to have everything under warranty and to avoid a fight with the mechanic (who by the way said that I could not refuse the Throttle Body cleaning because he already started), I accepted the work.

But now I have my doubts about the whole thing, the EGR they "supposedly" installed does not seem that new so I am wondering if they even changed it. As for the Body Throttle cleaning it seams for 34,500 mi vehicle it should not be that dirty. Plus, would it be a big coincidence that the Engine Light came ON just after the accident? Could it be a loose hose or something else? or am I just too paranoid about getting screwed by Auto Mechanics (..because I had lots of sour experiences in the past..)

BTW I am an aircraft mechanic (Airbus A320/A300/A340) so I am not a total newbie, but I do accept I do not have the time, tools, manuals or expertise to do the work myself on the minivan, plus if the warranty covers it then I don't care. If it's something simple and do not require specialized tools , or lifting the vehicle then I'll do it myself after I get the Factory Repair Manual...


If you guys are kind enough of give me your opinion I would appreciate it..

Thanks,

Rafael

[96Grand]

The question that you need answered is, what could cause the P0404 and P0405 codes, even if the EGR Valve is good?

Something is causing the EGR Valve to either stick or become in-operable.

There are many reasons that could cause this problem to occur.

This engine uses an Exhaust Gas Recirculation (EGR) system. The EGR system reduces oxides of nitrogen (NOx) in engine exhaust and helps prevent spark knock. The system allows a predetermined amount of hot exhaust gas to recirculate and dilute the incoming air/fuel mixture. The diluted air/fuel mixture reduces peak flame temperature during combustion.

The EGR system consists of:


EGR tube (http://www.alldatadiy.com/alldata/AFI~V6602690~C30621~R0~OD~N/0/41746574/56417202/56417205/56419253/34853741/34857029/34857699/56492591) (connects a passage in the intake manifold to the exhaust manifold)
EGR valve (http://www.alldatadiy.com/alldata/AFI~V6602690~C30621~R0~OD~N/0/41746574/56417202/56417205/56419253/34853741/34857029/34857699/34872079)
Electronic EGR Transducer
Connecting hoses
The Electronic EGR Transducer contains an electrically operated solenoid and a back-pressure transducer. The PCM operates the solenoid. The PCM determines when to energize the solenoid. Exhaust system back-pressure controls the transducer.

When the PCM energizes the solenoid, vacuum does not reach the transducer. Vacuum flows to the transducer when the PCM de-energizes the solenoid.

When exhaust system back-pressure becomes high enough, it fully closes a bleed valve in the transducer. When the PCM de-energizes the solenoid and back-pressure closes the transducer bleed valve, vacuum flows through the transducer to operate the EGR valve (http://www.alldatadiy.com/alldata/AFI~V6602690~C30621~R0~OD~N/0/41746574/56417202/56417205/56419253/34853741/34857029/34857699/34872079).

De-energizing the solenoid, but not fully closing the transducer bleed hole (because of low back-pressure), varies the strength of vacuum applied to the EGR valve (http://www.alldatadiy.com/alldata/AFI~V6602690~C30621~R0~OD~N/0/41746574/56417202/56417205/56419253/34853741/34857029/34857699/34872079). Varying the strength of the vacuum changes the amount of EGR supplied to the engine. This provides the correct amount of exhaust gas recirculation for different operating conditions.

This system does not allow EGR at idle.

The EGR systems can operate at all coolant temperatures above 60°F as long as the battery ambient temperature is above 7°F.

I would start there, w/ the EGR System itself... inspect the vaccum hoses,solenoid, and all other components for signs of damage.

A clogged fuel filter or bad gas could cause the EGR to malfunction temporarily until either the bad fuel is passed through the system or the fuel filter only gets clogged on a temporary basis, which will cause the EGR Valve to work overtime or get stuck.

I also think a bad spark plug or PCV would cause the problem, so check them as well.

I also had a similar situation, once my MIL came on for my 96 Grand and gave me the Catalytic Converter Failure code. I looked at everything, pretty much everything was new at the time and I couldn't find the problem. I found (through trial and error) that if you top off the gas tank too high, it will do it everytime. I guess it floods the engine a bit and causes the code. I wouldn't be surprised if this is what caused your situation.

Keep us informed as to what you find.

:rck:

[rtelles]

Thanks a lot for the quick and complete information you provided me 96Grand. I will most definetly make an exhaustive inspection this weekend (only free time I have) and try to determine the real cause of the Check Engine Light...

It's a real shame I do not have access to the Factory Repair Manual, and also to the fact that cars don't have a proper Troubleshooting Manual like planes do... it would make it so much easier to determine the cause of the problems..

Thanks again and I will most definetly post my findings here.

Rafael