Check Engine Light Stays On (2 Viewers)

[Brian Macgyver]

FYI:
First, once your computer sets a code, the light will come on every time you start until you do something to reset it.
Second, there is a way to reset. Remove the EFI fuse in the fuse box under the hood while everything is off. Do this when the engine is warm. It should erase the code, as well as all other engine running parameters. The engine may not run normally for a while on restart. It will recover.
Third, there are several chronic codes that set on OBD II 80's from year 95 1/2 up. One is EGR code 0402. Mine does it often. On first start up at under 45 degrees or so it will open the EGR while still cold. This sets the above code for excessive EGR flow. It means that the EGR opened when the engine was not warmed up. In real terms it means that I was in a hurry and didn't warm up the engine for 3-5 minutes before driving. If I do that, then I have no problem.
Reset your computer and watch for the light to come back on. Note the conditions when it does. If it comes back on the first time, then you have an immediate problem that must be dealt with.
If it takes a while, then note the conditions under which it comes on, have the parts store read the code and get back to us here. Somebody on MUD will know what the problem is.

 

[smokethedog]

FYI:
First, once your computer sets a code, the light will come on every time you start until you do something to reset it.
Second, there is a way to reset. Remove the EFI fuse in the fuse box under the hood while everything is off. Do this when the engine is warm. It should erase the code, as well as all other engine running parameters. The engine may not run normally for a while on restart. It will recover.
Third, there are several chronic codes that set on OBD II 80's from year 95 1/2 up. One is EGR code 0402. Mine does it often. On first start up at under 45 degrees or so it will open the EGR while still cold. This sets the above code for excessive EGR flow. It means that the EGR opened when the engine was not warmed up. In real terms it means that I was in a hurry and didn't warm up the engine for 3-5 minutes before driving. If I do that, then I have no problem.
Reset your computer and watch for the light to come back on. Note the conditions when it does. If it comes back on the first time, then you have an immediate problem that must be dealt with.
If it takes a while, then note the conditions under which it comes on, have the parts store read the code and get back to us here. Somebody on MUD will know what the problem is.

Brian,
I fixed my 402 as a result of this post, you might want to check it out: https://forum.ih8mud.com/showthread.php?t=132135&highlight=402
hth

 

[Beowulf]

One is EGR code 0402. Mine does it often. On first start up at under 45 degrees or so it will open the EGR while still cold. This sets the above code for excessive EGR flow. It means that the EGR opened when the engine was not warmed up. In real terms it means that I was in a hurry and didn't warm up the engine for 3-5 minutes before driving. If I do that, then I have no problem.

BM,
Just to clarify so others don't assume that your P0402 is "normal", the P0402 means something is broken in the emissions system of the vehicle and it needs to be repaired. A properly functioning vehicle will not throw any codes during normal use and "warming up the engine for 3-5 minutes before driving" is not a requirement. You have something broken in your EGR system if you are getting a P0402/P0401.

-B-

 

[latinoguy]

I just pulled the code this morning and got a PO401. Insufficient EGR Flow
OBDCodes.com gives the following info.

Causes

A code P0401 most likely means one or more of the following has happened:

* The DPF (differential pressure) sensor is faulty and needs to be replaced
* There is a blockage in the EGR (most likely carbon buildup)
* The EGR valve is faulty
* The EGR valve may not be opening due to a lack of vaccuum

Possible Solutions

In fixing this code, it is quite common for people to just replace the EGR valve only to have the OBD code return. The EGR valve is not always the culprit.

* Use a vacuum pump and pull the EGR valve open while monitoring engine RPM's. There should be a noticable difference in RPM's with the EGR open
* Clean out the EGR valve to remove deposits
* Replace the DPF sensor
* Replace the EGR valve

I DO NOT NOTICE DRIVABILITY PROBLEMS SUCH AS PINGING.

Searches on forum suggest that I start by replacing the EGR Valve. Correct?

 

[Driley]

Start by checking all of your vacuum lines.

Does your system look like this? Then you need the new blue top modulator (it is located at the center of the picture with 4 hoses attached to it - this was before installing the new one).

Check, clean or replace the vacuum lines first. I had the equivalent code on my '94 (code 71) and never had any detrimental effects from it (just hated the CEL on all the time). I recently used compressed air to blow out the vacuum lines and installed a new modulator (~$50.00 from cdan) and so far my CEL has been dark. It will come back again and then I will remove the throttle body and clean. After that I will dig deeper.

This process is covered quite extensively in the faqs. Or just type EGR in search and start reading.

Riley

 

[Beowulf]

Searches on forum suggest that I start by replacing the EGR Valve. Correct?

I would be very, very interested in where you found a post here in the 80-Section that said to start by replacing the EGR valve.

-B-

 

[john_eckels]

I just came back from EGR Hell. 2 Weeks and no code. I will save you some searching. The 2 most common probles are the EGR modulator, (there are threads on how to troubleshoot this), and the VSV valve which cancels the EGR. Here is how I found out my VSV valve was bad. When the engine is hot after driving, put your finger on the metal tube going into the EGR valve. It should be really hot. If you have EGR underflow, it will just be warm because exhaust gas is not circulating through it. Also, the EGR vavle itself should be good and hot if the exhaust gas is curculating through it. If it is really hot, it could be your temperature sensor. If it is not hot, do the following: Disconnect the vacuum line from the EGR valve, the one on the driver's side that runs down to the intake manifold (which leads to the VSV valve). Use your finger to plug the end of the EGR valve that you just removed the vacuum line from. This causes the same effect as the VSV valve closing which should turn on the EGR. Rev the engine for a short while with your finger plugging the end, if the EGR is functioning, the metal tube will start to get hot due to exhust gas flowing. If this happens, it is highly likely that you VSV valve is stuck open. If this does not happen, it is highly likely that your EGR valve is not getting the proper vacuum to it. This means that you should troubleshoot the EGR modulator, and look for plugged vacuum lines and ports.