I know this is a lot of info to read, but please bear with me, as I think its all important to figure out what is really causing the problem.


1998 Chevy Blazer, 172k miles. The blazer is giving a P1404 code, meaning the EGR valve spintle is stuck open, but I am really starting to doubt that's the real issue!

I cleaned the throttle body, MAF sensor(scanned it with my neighbor's scan tool and a code came up with something to have to do with the MAF sensor, that code cleared so that's fixed...)

I replaced the EGR with one I pull out of another 98 chevy from the wrecking yard, did not fix it( I have tested both EGRs and all tests seems to indicate that they are both functioning.



I checked for leaks and all the leaks that I could find were coming from old, riddled, broken hoses and they were replaced.

I cleaned the EGR valve with throttle cleaner, erased the code, but it keeps coming back after driving it for less than 5 minutes every time after erasing the code.


I found this website(Part 1 -How To Test the GM EGR Valve -Buick, Chevy, Olds, Pontiac) and i followed the guide for testing the EGR, everything points to the EGR functioning correctly, BUT I did find an issue with circuit E(12 volt power source), which is strange. When I test circuit E wire without the EGR connected to the connector, it reads 12 volts, which is what it should be reading, but here is the problem, I believe, when I test the same circuit while the EGR is connected to the connector, it reads 30 volts, which is way too many volts, and I think is the where the issue is. The guide mentions that if it is reading under 12 volts, then that's the fault, and can be caused by a short between the PCM and EGR connector, but it doesn't say anything if its reading more than 12 volts.

Now, if there is a short, which makes sense, because when I took the chevy to the mechanic t, his Snap-On scanner wasn't able to communicate with the vehicle, , which he then determined there was a short and unplugged a cable from the back of the cig lighter, and that fixed that little issue.

 

Does anyone know why circuit E on the connector is reading 30 volts...........?

 

Here is the flow chart straight from the GM dealer issue shop manual. There is only one page of tests, making it one of the quicker DTC's to diagnose. Follow the steps and you'll find the problem. https://blazerforum.com/forum/diagno...plained-35133/

 

well, i already ran some tests and everything seems to point out that the EGRs are fine.

What I need to know is if this problem can be because the EGR valve 12 volt circuit is showing 12 volts when the EGR is disconnected from the connector, but reading 30 volts when connected to the connector.

Can this be a short?

I've read countless of websites already, but have not been able to find one that mentions anything about this

Help would be greatly appreciated.

 

"well, i already ran some tests and everything seems to point out that the EGRs are fine."


The DTC is indicating the valve position is above the limit when the valve is commanded closed, (.29 volts is the limit). If voltage is above that, the DTC will set.


The only way you'll see voltage above 14.2 volts, is if the alternator overcharges due to an internal problem, (voltage regulator, rectifier, etc). Even then, the highest you'll see is approximately 18-20 volts. Is it possible your DVOM is either on the wrong scale, or the auto range function is switching to a lower range and you're not noticing it? You may be interpreting the reading, (decimal point) incorrectly. Here's why I ask:

This is from the flow chart:


CONDITIONS FOR SETTING THE DTC

* The EGR pintle position voltage is 0.29 volt or more with the EGR valve commanded closed.
* The above condition exists for more than 10 seconds.





When you perform the actions in step #2 of the flow chart, what are the results on the scanner?

 

Ive ha double checked that the DVOM is at DC volts and it is actually reading 30 volts whenever the EGR is plugged to the connector... I'm not seeing things, at least I hope not! lol.

I don't have scanner than has the function to command the EGR, but is there a way to command it manually without a scanner?

Also, the SES light turns off after the blazer has cooled down for a few hours/overnight and turns back on after I take it for a ride. Can this be a sympton of the EGR sticking.....?

 

30 VDC is definitely a puzzle.


The only way to command the EGR valve is with a bi-directional, (high dollar) scanner.


EGR is constantly monitored when the engine is running. If there is a malfunction, it will set a DTC in memory and turn the light on. Once the DTC is set, it will remain in memory for a programmed number of drive trips without a failure. If it seats properly after a cool down, the light will not come on, (DTC will remain in memory) until it malfunctions again. It is quite possible that the pintle is sticking. Monitoring live EGR data stream, which can be done with most scanners, will show the out of range condition when the light comes on. Could very well be bits of carbon lodging in the pintle seat, if that's the case, installing a screened EGR gasket would solve the problem.