Can bad EGR cause trnsmission problems?
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. ...
Forum Discussion
It appears this transmission uses a vacuum modulator. A leak or a bad modulator itself will cause shift issues. Can shift issues interfere with the transmission going into overdrive?
Diagnostics may want to include taking vacuum readings at the EGR valve and at the modulator vacuum line connection. Correct vacuum signals eliminate the chance of a vacuum leak causing the problem but do not eliminate the possibility of having a bad modulator itself.
A pro-grade OBD scan might be wise. The above is just a hint about receiving confusing OBD scan results - where to look next.
