95 chev monte carlo digital egr valve code set

Hi, I have a 95 chev monte carlo, 3.1 motor, 129.000 miles on vehicle, the service engine code reads egr solenoid 1,2,3 failure.. I changed the egr valve twice and the egr ports look clean..also the code only set (service engine lights) when on the highway and after I coast a short distance (tenth of a mile). I must be going at least 50 mph and then let off the gas petal. In the city the service engine light does not come on. I have checked the voltage to the egr valve and it is 12 volts.. have any ideas? thanks what code?I believe on that engine and year that there is a code for each of the three solenoids.Each one has a code relating to a certain solenoid.I think it is up around 73,74,75.Need the actual code number?This should be OBD 1.Any driveability problems?The PCM looks at map during de-acceleration to see if egr flow.Let me know.
thanks for helping, no drive ability problems, and obd 1 is giving me three codes 75 76 77
The reason for the light coming on during decal, out on the highway, is because that’s when the computer performs its diagnostics, on the EGR system.
The way the computer does this is, during a decal it will open the solenoids; if they are working and there is no blockage; exhaust gases will be allowed to flow into the combustion chamber. While this is happening the computer monitors the O2 sensor(s) looking for an abrupt change in its readings. If the computer doesn’t see the expected change in O2, on comes the light and the code is set.
About the easiest way to check the electrical portion of the system is with a scan tool that has bidirectional capabilities.
With the scan tool you would put in a request to the computer too energize the solenoids one at a time. When the computer does energize one of the solenoids, you should be able to hear that solenoid click and the engine rpm drop or the engine may even stall, depending on which solenoid you requested.
If you can hear the solenoids clicking when energized and you believe (checked) that they are actually opening; you may have a plugged intake passageway and the exhaust gases cannot flow into the cylinders. I’ve had to clean quite a few upper intakes on these 3.1’s; the carbon inside the passage way will be just as hard as cement but it will come out with a bit of effort.
To check whether the solenoids are actually opening; remove the valve from the engine, leaving it connected electrically and then command the computer to energize solenoids 1, 2 or 3. Looking at the bottom of the valve, you’ll be able to see the port(s) open & close; as they are turn on & off.

There are ways of checking whether the computer has the ability to energize the EGR solenoids but it would mean connecting a test light across the EGR solenoids connector. Having the test light positioned in a place that can be seen from the driver’s seat. Then driving the vehicle at different speeds until the computer decides to energize that particular solenoid; long and very dragged out process.
The pcm monitors the map to look for changes in egr during de-cel not the 02 sensor.Something is affecting all three solenoids electrical or the intake is plugged.A scan tool with enhanced capabilities would be needed to do bi-directional controls to command egr solenoids on and off to check to see if the pcm has control and also to check interconnecting wiring and egr itself.You can do a few electrical checks.Disconnect egr electrical connector and with key on engine off probe terminal (D) of electrical connector,it should be a pink wire that goes to fuse 9 20 amp to ignition with a test light hooked to a ground or battery neg.when you touch terminal (D)test light should light.Next take test light and hook to b+ terminal and touch egr electrical connector terminals A,B,C test light should be off on all three terminals.A-LT BLUE WIRE.B-BROWN WIRE.C-RED WIRE.If no voltage on 1st test then check fuse and wiring.If test light is on during 2nd test there is a short to ground.If all check okay then maybe electrical connector connections or maybe plugged egr passages.A scan tool with enhanced capabilities would be needed to check egr electrical condition and pcm control of.
 

I stand corrected yes the MAP is what’s monitored on this particular model.
Maybe the next time you want to correct a post (which you should) you could add an explanation; so that the less knowledgeable people then you can understand where I made the mistake in my post?
Regardless of which is monitored; the end result and test procedures are the same.