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2005 Buick Terraza Check Engine Light with low EGR Flow code

I am having a hard time getting the low EGR flow check engine code to clear. The EGR valve and tube from the exhaust manifold were replaced, the wiring harness verified, the passage channel between the EGR valve and the intake manifold cleaned out…but the check engine light remains…any ideas what to try next?

What is the specific code?

Hopefully you did actually clear the code after the work. Otherwise you have to wait a certain number of drive cycles for the PCM to clear the code.

How was the wiring harness verified?

I don’t recall the code number, but each time I would do something that I thought would correct the issue, I would go to my local O’Reilly’s auto parts store to borrow their code reader and clear the code. The check engine light would go away…for a short period of time and then would come back on. The replacement GM valve was a Siemens valve and the original valve was a Delphi…and the new valve came with a short 5 wire harness to tie into the existing wiring harness since the molded connector that attaches to the valve was different than the original factory connector. I used a digital multi-meter to check resistance through each of the 5 conductors on the old valve and then matched conductors with similar resistance on the new valve. I later discovered that GM had a service bulletin to address an incorrect wiring diagram that came with the new valve, but as it turned out, I had it wired correctly and the service bulletin just confirmed that.

Ok. I would next do more to verify the wiring / electrical end. This is a pretty thorough walk-through complete with appropriate voltages and such: Having replaced the valve and stuff already, not all will apply. But it has the specs for things like power supply and the sensor wire and all.

There is an updated EGR that also requires a computer flash. TSB 06-06-04-003D

Use wiring instructions in the TSB, not the EGR kit.

Thanks for the advice guys. I went to the diagnostic websight recommended by Cigroller and printed it out. This past weekend I started going through the diagnostic tests. When I checked the pintle position sensor during a roadtest, I did not get the same range of voltage as the procedure indicated. Instead of varying from .6-.9 up to 4-4.5, I started with a voltage around 3 and had a range while driving of 2.68-3.18. The individual has his contact info. on the website, so I was going to try corresponding with him. Does anyone else have any suggestions?

I would check out the TSB noted by rattlegas. If nothing plays out there, unfortunately I see a Tech II scanner in your future - i.e. the need to fork over a hefty diagnostic charge.

Is the car running ok? And I mean all of the time. Smooth idle? Normal power? No power losses, even if mild? I believe that sensor is just a simple potentiometer kind of thing - the signal just varies directly with the pintle position. So if the voltage stays higher than it should, and the new valve you installed is not defective, then you would be getting something like a rough idle - IF it is accurately reading the pintle position. Did you do the key on engine off test with valve removed to manually actuate the pintle?

If this person leaves his contact info on the website I can’t imagine that dropping an email would be a problem.

I think the comments above represent more knowledge about this topic than I possess, but on my Corolla there’s a fairly complicated vacuum arrangement that controls the EGR. For example, there’s a thing called an EGR modulator, which is sort of like a mechanical-transistor for making slight adjustments to the EGR vacuum, depending on throttle position, coolant temp, EGR temp, etc. So if the above ideas don’t pan out, have your mechanic check all the vacuum paths that control the EGR. On my Corolla one of the paths is internal to the throttle body, and can clog up with gunk over time. I had to remove the throttle body for another reason a while ago, and notice that path was semi-clogged, so I cleaned it out with some throttle body cleaner.

Cigroller and George SanJose, thanks for the responses.
Cigroller, the TSB is essentially instructions to verify/correct an incorrect wiring configuration that came with the new valve. Instead of following the wiring diagram when I installed it though, I matched resistance readings between the 2 valves and wired it accordingly…and verified it with the info. in the TSB. The one test I have not done yet though is the manually-activated-with-an-external-power-source test. I was going to borrow an Altech voltage source from one of the electricians I work with…we use many instruments to make Budweiser. I don’t know, but I assumed the pintle position indicator would vary throughout the range of the valve movement on a scale of 0-5 volts…i.e the applied reference voltage. I thought I would apply a variable voltage to move the valve and use my Fluke DMM to check the position. I’ve taken the vehicle to a dealer twice already…the first time they needed to program the PCM for the new valve type, i.e. Delphi to Siemens, and the second time I brought it in to have them double check their work. They told me they ran a diagnostics test on the valve and verified its operation. I assumed they had some sort of diagnostic test unit that they used to do the same test I am going to attempt with the external power supply and the DMM. The one issue I have though is correlating an input voltage to the pintle position voltage…I thought I’d just assume a linear reaction of both the valve to the applied voltage and the pintle position. Any thoughts?

First, I have a plenty of direct experience with the vacuum actuated EGRs, and especially the Ford system. But my knowledge of the GM electronically actuated valve is basically “book knowledge.”

That said, I think that the problem with using the DMM to verify the pintle position remains indirect. In principle, it should work - but only if your new EGR is not defective. I would probably do the test where you remove the valve, connect it to power, and manually actuate the pintle while observing the return voltage. And yes, as I understand it, it should just be a very direct variation from something like .6-.9 V or so up to / close to 5V. By all means, however, feeding it a controlled ref voltage is also a good idea.

Others here with more hands on experience with the GM system may be of more use than I.

I’m still wondering whether or not you are getting any driveability symptoms that might be associated with EGR problems.

The vehicle seems to run OK, but it’s hard to say for sure…it is a 2005 with 225,000 miles on it. It does seem to have decent power…although at times it can idle a little rough. I’m kind of hoping that’s due to a bad EGR valve and that when I resolve this issue, it begins to run even better. This past weekend I used an instrument calibrator. I tried to source a variable voltage into the removed EGR valve, but the calibrator displayed a short circuit detected…I guess the coil resistance was too low or the calibrator I used had some sort of current limiting circuitry. Nonetheless, I did take a simple 9 volt battery and stroke the valve with it. While doing this, I checked the resistance across the pintle position indicator…with very little change. Based on this plus the voltage reading I got from the pintle position sensor with one of the other tests while driving…i.e. it only fluctuated slightly and did not vary from .6-.8 to 4-5, I am going to replace the valve. The valve was bought from Auto Zone and has a lifetime warranty.

Is your Buick subject to periodic emissions testing? If not, this is an issue you can ignore…And while you are ignoring it you can start looking for a replacement Delphi valve with the correct wiring connector…

Agreed Caddyman…there is no emissions testing in Illinois. Although I haven’t given up on resolving it, we have continued to drive it. The valve I replaced last summer has a full lifetime warranty, so I am pursuing a replacement from AutoZone.

Another low exhaust gas flow issue. This vehicle, 2005 Buick Terraza minivan, now has 290,000 miles on it…and still runs well, albeit I installed a Jasper transmission 2 years ago and had to do a head gasket job in the fall of 2015 as well. I am tacking this note onto the notes I had from 3 years ago when I had an issue with the EGR system…it’s back. I am getting a low exhaust gas flow indication and have replaced the valve, twice now, and cleaned the passageway between the valve and the intake manifold but the light does not go away. I thought the system used the pintle position feedback to indicate that both the valve was working as being instructed by the PCM and that it had sufficient exhaust gas flow, but maybe that is not the case. Is there another instrument that indicates sufficient exhaust gas flow or is there something else I could be checking to get to the bottom of this?