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1997 Geo Metro code P0400

Tiny
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  • 1997 GEO METRO
Engine Performance problem
1997 Geo Metro 4 cyl Front Wheel Drive Automatic

i am working on a 97 geo metro lsi with a p0400 code that refuses to go away. Before I got the car the egr valve, the vacuum modulator valve, and the pair of solenoids under the modulator valve had been replaced with new from the dealer parts. I noticed the egr valve doesnt open under wide open throttle, in gear or in neutral(after engine is warmed up).I can open the egr valve with a vacuum pump and the engine stumbles. The solenoid that controls the egr has vacuum to it but doesnt open under throttle, however I can ground one of the wires to that solenoid and it clicks open and the egr opens. I have replaced a few vacuum lines that were damaged. I have the usual question. What now? Haha, what controls the solenoid? The pcm? Thanks for your help in advance.
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Wednesday, April 7th, 2010 AT 2:21 PM

20 Replies

Tiny
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Yes, the PCM does. Put your vacuum gauge on the hose that would plug into the EGR valve and drive the car. EGR should come on at part/light throttle cruise, around 40 mph. How bad does it make the engine stumble when applied at idle? It shoudl almost kill the engine
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Wednesday, April 7th, 2010 AT 10:02 PM
Tiny
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Ok, I will put a vacuum guage on it and see if its applying vacuum while driving. And the engine does nearly stall when I open the egr valve. Thanks!
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Wednesday, April 7th, 2010 AT 10:16 PM
Tiny
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Let me know what you find. Remember. Part/light throttle cruise around 40
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Thursday, April 8th, 2010 AT 7:25 AM
Tiny
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Ok I drove the car with the vacuum guage on the hose that goes to the egr valve, there was no consistent vacuum change. I say that because there was only one time while duplicating the part throttle at about 40mph that the guage shot to 20 inches of vacuum, stayed there untill I came to a full stop then returned to zero. At that point I pulled over and made sure the vacuum line wasnt pinched, it wasnt. I tried duplicating the conditions a few more times, no movement from the vacuum guage. I unplugged the connector on the solenoid that feeds the egr and put a voltmeter on both pins. While idling it reads 1 volt, at part throttle it reads 2 volts.I didnt do this part while driving.
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Thursday, April 8th, 2010 AT 12:54 PM
Tiny
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You have good source vacuum to the egr control solenoid? If so testing to see if the solenoid is being activated by the ECM is the next step
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Thursday, April 8th, 2010 AT 7:48 PM
Tiny
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Yeah I have good engine vacuum at the solenoid. This car is going to start to affect my sleep, haha. How should I check for proper ecm control?
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Thursday, April 8th, 2010 AT 8:51 PM
Tiny
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Power at the EGR solenoid when cruising. It is usually the EGR solenoid on GM's, but dont quote me on that. LOL. If you have good vacuum into it but nothing solid out, it may be sticking.
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Thursday, April 8th, 2010 AT 9:38 PM
Tiny
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Yeah thats exactly what has me so twisted on this, its a pretty cut and dry kind of thing. Usually. Haha i'll drive it and moniter voltage the same way I checked for vacuum. What about a control problem with the ecm? Cause I can ground the one wire at the solenoid and the solenoid opens and opens the egr. Thanks for your patience.
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Friday, April 9th, 2010 AT 12:19 AM
Tiny
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ECM most likely triggers with ground, its easier on it.This system has a pressure transducer (See Pic).


https://www.2carpros.com/forum/automotive_pictures/1639_geo_1.jpg



Has this item been checked? these burn out alot, they are common on Toyotas. Has 3 vacuum lines on top and 1 to the EGR pipe(exhaust) on the bottom.
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Friday, April 9th, 2010 AT 7:28 AM
Tiny
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Yeah the pressure transducer has also been replaced with a dealer part. I drove it again with a voltmeter on it. I hooked it up to one wire and the battery ground, drove it, no change. Then hooked it up to the other wire, also no change. Hopefully that is the right way. It read on both wires battery voltage the entire time, 14.01. At least the alternator works, haha. Another thing is I got a hold of a gm tech 2 scanner and I can active command the solenoid on and the engine dies.
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Friday, April 9th, 2010 AT 1:54 PM
Tiny
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Did you drive it with the scanner on to see if the ECM is commanding it on?
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Friday, April 9th, 2010 AT 2:58 PM
Tiny
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Wow, what an excellent thought! I really should have thought of that! Ugh! I will do that in the morning. Thank you thank you.
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Friday, April 9th, 2010 AT 9:19 PM
Tiny
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Having access to a scanner can make all the difference. Let me know what you find
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Saturday, April 10th, 2010 AT 10:16 AM
Tiny
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Ok, I drove it with the scan tool and watched the pid for the egr control valve and it switched. It was odd though, it originally started "off" then would switch on when I accelerated. Then it started with "on" but still switched. Also I ohm tested the red and black wire for the vacuum control valve between the ecm and the valve, 0.03 ohms and the green wire for the other solenoid had 0.04 ohms. With the connectors disconnected. I took the egr off again and rechecked if it was clear, it was. I started it with the egr valve off, just for grins, and I had vacuum at one port and presseure at the other.
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Monday, April 12th, 2010 AT 9:11 PM
Tiny
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Is the MAP sensor good?If not it wont see the intake pressure difference and will set this code. Also is this a California car? Has the ECM been replaced? A non-Ca ecm will run fine until it commands EGR then it will set a code. What happens when you command EGR manually at idle with the scanner? Also what vacuum reading do you get at the valve when you do this?
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Tuesday, April 13th, 2010 AT 6:45 AM
Tiny
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Not sure if the map sensor is good, I know it hasnt been replaced. When I command the egr open with the scan tool the engine stalls, or nearly stalls. Its not a california ecm, and they havent replaced that either. I havent checked vacuum at the egr when I command it on, im guessing that I get engine vacuum though since it opens and stalls, I will check though.
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Tuesday, April 13th, 2010 AT 12:01 PM
Tiny
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Running out of stuff to check. Lol any exhaust work done to this car? Just wondering about backpresure to the transducer at hard throttle vs. Light cruise.
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Tuesday, April 13th, 2010 AT 1:22 PM
Tiny
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I know huh! This is normally an easy repair. No exhaust work done though. The car runs great other than the light. The map sensor comment has my attention though.
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Tuesday, April 13th, 2010 AT 9:31 PM
Tiny
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According to Mitchell thats how the ECM sees the EGR working, with the pressure/vacuum change in the intake. But witht his one, dont quote me on anything. LOL
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Tuesday, April 13th, 2010 AT 9:38 PM
Tiny
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How should I test the map sensor? Sorry for the long delay, they have been enjoying driving the car and i've been enjoying the break. Haha
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Friday, April 30th, 2010 AT 7:14 PM

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