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CEL P0401 help

J

jsark

CEG'er
Joined
Jul 1, 2002
Messages
52
My '98 with 120k has had a steady CEL for a month or so now. Finally got to Autozone and had the codes read (I also have their nifty print-outs):

P0401 - Insufficient EGR Flow
P0420 - Catalyst System Efficiency below Limit - Bank No 1
P0446 - Evaporative Emission Control System Vent Control malfunction

Although I desire for this thread to focus on the P0401 code, I posted them all in case they're relevant to one another. Also, bear in mind I'm a little behind the knowledge curve on emissions systems, so please - if you have any guidance to offer, don't assume I understand acronyms or know where various parts are located on the vehicle.

I don't possess any testing/diagnostic equipment, let alone the knowledge to use it. I am however, quite capable of swapping out parts, etc.

So, P0401 - Insufficient EGR Flow...

Should I begin by cleaning something? Replacing something?
 
for the p0401 remove the tb and clean the egr passages behind it.

for the p0420 it maybe time for a mil-eliminator and it indicates a bad cat

not sure on the lest one, but I would locate said vent and check it out to see if it needs to be replaced.
 
If you have a loose evap hose you will also have less vacuum..

that = insufficient flow for the EGR which would also trigger an 0446

It could do the same in reverse, too, if the EGR tube/vacuum connections were leaking.
 
@BrApple:

What is a mil-eliminator?

@Ray:

I'm not familiar enough with the emissions system's anatomy to know for certain which hoses/lines are which. I'll do a forum search about this when I get home, but if you know of any threads with images to point out where these hoses/lines are, that'd be great.
 
P0420

P0420

I was having problems with a reaccuring P0420 code. Doing some research on Google led me to TSB 01-9-7. This relates to a variety of codes and lists possible causes. Under 0420 heading the very first item to check or replace was the Engine Coolant Temp unit (ECT). Sounds weird that the coolant temp had any bearing on the cat effiency. Figured what the heck. Got a new sensor, drained some of the coolant, put thread seal on the sensor, installed and replaced the harness. End of problem. Worth a look.
 
Okay, with my own forum searching and the additional input from everyone, there is quite a bit for me to digest, so let me ask for a little additional help (couldn't find enough info via search):

1. Could someone briefly describe, in detail, the process of cleaning the EGR passages? I know what/where the the TB is, but I've not removed it before, so I don't yet know what I'd be looking for once it's off.

How many passages are there? What should I use to clean the passages effectively, etc?

2. Could someone either post a photo or describe in detail where the hoses/lines/tubes are which would affect EGR vacuum? I think I know what/where the EGR cannister is, so would all flexible lines connecting to it be worth replacing?

I know this is old-hat for many of you, but I've done little to nothing with auto emissions systems over the years. New stuff for me.

Dan - where is this ECT unit you speak of? About a year ago, I replaced the coolant reservoir due to an ever-present coolant light. Isn't the sensor integrated into the reservoir?

Thanks, people. With all the help from this forum, one of my '98s is running like a champ. Hope to get the other one running that way, too!
 
ECT

ECT

Dan - where is this ECT unit you speak of? About a year ago, I replaced the coolant reservoir due to an ever-present coolant light. Isn't the sensor integrated into the reservoir?


The sensor in the resivor is for low coolant level. It has nothing to do with the temp of the engine coolant. The ECT (Engine Coolant Temp) on my car, 96 v-6 with manual trans is located on the fire wall side of the engine. It is above the starter and below the throttle body. There is a sensor in the water tube under the throttle body. This is the temp sending unit for the temp gauge. I believe there are several recent posts that show a picture of the ECT. Also the auto zone web site shows the approx. location with how to. Good luck Dan
 
update

update

For the sake of others who may need to perform this procedure, I thought I'd post before-and-after shots of my EGR port cleaning job.

I don't know yet if this will reconcile P0401 or P0420 (PCM self-test is not yet complete), but there's no doubt this needed to be done.

Before:

egr_before.jpg


After:

egr_after.jpg
 
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