P0128 and P0404 code errors HELP!!!!! [Archive] - GrandAmGT.com Forum


View Full Version : P0128 and P0404 code errors HELP!!!!!

01-04-2006, 08:59 PM
Here is the deal I know what the codes are could be an Egr valve or coolant temp sensor going bad. Here is the problems I am having with my car. its a 2002 Gt with an Cai Mod and a resistor in the AIT sensor. I am having no acceleration when I press on the gas. its like there is a fuel mixture problem. its has no go any more. i have to press lightly on the accelerator to make it move takes forever to get up to 60 or 70 mph can barely make it move. I can also seem like i can hear a hissing if i press on the gas and there no power. i can floor it and the rpm will start to go but its liike the engine is running way to rich!! and have to back off to adjust the air flow. I have a freind who has a 2001 monto carlo with the same engine so he let me borrow his EGR value and same problems. Its like there too rich and not enought air. I can't get the car to go over 3000 on the tach with the car moving under load. If I just sit at idle i can get it to 4k before the gov kicks in. This is driving me crazy i did read on the site the the EGR is determined by 3 other things See below. I am thinking that maybe the MAF is bad or the wires or something I checked but could not determine. Or the MAP is bad HELP ME PLEASE!!!!!!!!!!!

Exhaust Gas Recirculation (EGR) System Description
The exhaust gas recirculation (EGR) system is used to lower oxides of nitrogen (NOx) emission levels caused by high combustion temperature. The (EGR) system does this by decreasing combustion temperature.

The main element of the system is the linear EGR valve. The EGR valve feeds small amounts of exhaust gas back into the combustion chamber. With the fuel/air mixture thus diluted, combustion temperatures are reduced.

Linear EGR Valve
The linear EGR valve is designed to accurately supply EGR to an engine independent of intake manifold vacuum. The valve controls EGR flow from the exhaust to the intake manifold through an orifice with a PCM controlled pintle. During operation, the PCM controls pintle position by monitoring the EGR position sensor signal circuit. The signal circuit can be monitored with a scan tool as EGR position sensor. The EGR position sensor should always be near the commanded EGR position (DESIRED EGR POS.). If a problem with the EGR system will not allow the PCM to control pintle position properly, DTC P0404 should set. The PCM also tests for EGR flow. If an incorrect flow is detected, DTC P0401 should set. If DTCs P0401 and/or P0404 are encountered.

The linear EGR valve is usually activated under the following conditions:

Warm engine operation
Above idle speed
Linear EGR Control

The PCM monitors EGR actual position and adjusts pintle position accordingly. The PCM uses information from the following sensors to control the pintle position:

Engine coolant temperature (ECT) sensor
Throttle position (TP) sensor
Mass air flow (MAF)

01-05-2006, 09:35 AM
First thing I'd do is take out the IAT sensor mod... it's nothing but a stupid gimmic and it can contribute to problems like this. The P0128 is for coolant temp and the pcm sets this when the car has traveled enough distance at a high enough speed and has taken in enough air and the engine isn't hot enough yet. It measures air in grams per second which it arrives at using the reading from the MAF sensor for air velocity and the IAT sensor for air density and calculating the g/sec with some complicated formulas. If you have a CAI and you're tricking the IAT into thinking the air temp is different, you could be throwing off the air volume reading enough that the pcm thinks enough air has entered the engine by now that it should be hotter. Get rid of the IAT mod! Of course, you also want to check your coolant level, and it might be a sticky thermostat too. That's not that uncommon a problem and it's a cheap part to replace.

The P0404 code is for EGR open position performance. The pcm reads the EGR pintle open position and compares it to the commanded open position, and if it's not within 15% it sets the code. This usually won't happen unless there is an actual problem with the EGR so you shouldn't have to look anywhere else. Check the wires on the harness going to the EGR solenoid and make sure there's nothing melted or cut. Take the plug out and clean the contacts on the solenoid as best you can and put some dielectric grease on them then plug it back in. That will make sure it doesn't get shorted by water or corrosion, and that it gets good contact. If that doesn't work then the EGR valve might have carbon build up and need to be cleaned, or it might be defective and have to be replaced.

10-21-2006, 05:47 PM
I am having the exact same problem and I have no engine mods except a cone air filter, please post and tell me what fixed your problem, if you got it fixed. thanks.

10-24-2006, 08:46 AM
look since losty hasn't replied to my e-mail or post, can someone suggest anything else, I am about to take the egr valve out and clean it out. but I am open to if anyone is having the same problem and what did they find I already cleaned out the connector nothing significant happened, so my next task is pulling the egr and cleaning it.

11-03-2006, 07:00 AM
OK I pulled the egr vavle out cleaned in all out it opens and closes no problem. put a new gasket on it, and then put it back together. No real big change, we even put it on the snap on scanner and was able to open and close the egr, that all worked and did what it was supposed to do. SO PLEASE HELP ME!!!

11-06-2006, 02:10 PM
You know, I remember a time when you could post on this website and ppl would be able to help you. Now not so much!

11-06-2006, 02:21 PM
HOLY ****!! youre attempting to fix that thing? sorry man, i dont know how to help ya out. someone will chime in soon enough. ;crap

11-06-2006, 02:23 PM
What do you want us to do?
We cant diagnose your troubles through a CP screen.
All we can do is get you going in the right direction.

11-06-2006, 02:49 PM
this might help you a bit.