Can bad EGR cause trnsmission problems?

[haydoracin]

I have the MH listed in my signature i.e. Chevy 454 P series with I believe the 4L80E transmission. Recently experienced problem with not shifting into overdrive and intermittent Check Engine light. OBD scan shows bad EGR valve. Could this cause the shifting problem?

[enblethen]

Very few OBD tester can do the OBD-I modified as in P chassis.

[haydoracin]

Thanks again for all the responses. Sent a link to this thread to my mechanic so he can review. He's also a good friend and is open minded to outside input.

[PaulJ2]

Does engine come up to normal operating temperature? Some have the EGR as well as overdrive locked out until engine comes up to near normal operating temperature.

[enblethen]

Do a search for OBD I code 32.
That is what book says is EGR. Search and you will find other items that can set this code. One item is the MAP sesensor.

[MEXICOWANDERER]

Ask any ECU diagnostician...
"Do you have substitution parts for troubleshooting?"

Of course they do. OBD error code diagnosis is not cut and dried. I watched a top-tier diagnostician (Ed's Auto Electric - Lancaster, CA) go through a procedure with a car. Narrowing the field a substitute TPS, then MAP, followed by CPS, led him to a firewall bulkhead failed connector. End result - no failed parts, bad connector.

Without factory technical service bulletins the process is mostly guesswork. Without verification of vacuum values "guesswork" advances to almost total blindness.

[allbrandauto]

gm egr codes can set 2 ways one is by computer of the vehicle looking for reistance of egr soliniod second is by when egr valve opens intake manifold vacuum drops that's what computer is looking for again if cat. converter is clogged manifold vacuum dos not drop as quick and could set that code

[wa8yxm]

Not sure on that one.. The post above mine suggests but as I said I'm not sure.

Mex. You seem to know more about this than I.. (not all that hard I'm not an auto-tranny expert) so can a bad vacuum modulator cause an EGR error?

I only know on the car I had where I had an EGR issue there was no vacuum to the EGR it was a bi-metal operated thing.. but .. that was a 1992 chevy. And the problem was a stuck valve which freed itself so I never fixed it Or perhaps I did by messing with it (don't knwo) Do knwo it was very hot and I was towing max rated weight that day on a long (200 mile) Drive.

[time2roll]

Can a bad transmission cause an EGR code?

[MEXICOWANDERER]

Until I got smart in the early 70's I owned an automatic transmission shop (15 months). Modulators can fail in several ways. To ignore testing of the vacuum modulator would be a breach in diagnosis. Ownership taught me a lesson about employee unreliability - I quickly moved on to electrical and rebuilding. Diagnostics itself is an art form. But it is a discipline. Ignore the discipline and fail. Troubleshooting is unforgiving.

[wa8yxm]

Well.... IT was only a POSSIBLE solution (Vacuum modulator being affected by loss of vaccum) not the only one.

Failure to shift into overdrive can also be caused by lack of engine performance. It never senses the engine has the power. That however depends on the tranny. some are smarter than I am (Allison) some not so smart (most everybody else).

[MEXICOWANDERER]

Guess the advice about the vacuum modulator did not make an impression. 🙂

[haydoracin]

UPDATE!! EGR was replaced this afternoon. Codes cleared. Test drive resulted in "Service Engine Soon" light coming on 2 miles from the shop. Still not shifting into OD. Returned to shop and code scan resulted again with bad EGR. Engine runs fine with plenty of power. Will be later this week before I can get it back into the shop. Updates to follow:

Thanks again for all the responses.

[ScottG]

allbrandauto wrote:
I fully understand how the system works the leak at idle I'm talking about is when the pintal sticks open at idle caused by carbon build up or carbon in the seat causing the valve not to close anyway the op is trying to find out why the trans. wont go into high gear

OK, I understand that but that particular failure mode isn't the only way it can fail. More often, the diapragm gets a hole in it.
One way could effect it at idle and the other wont.

[wa8yxm]

Can an EGR issue cause shifting issues.... Complex answer

It can cause a general loss of power in the engine the result is you open the throttle more and on a Gasoline engine this lowers manifold vacuum. On some transmissions this vacuum helps to control or operate the clutches.

As for your specific Engine and Transmission. I do not know

But I'd get the EGR fixed as it can affect MPG