Check engine light & OD

[jsummers72]

yesterday I got a ck eng light & about the same time I noticed the transm wouldn't shift into Overdrive. It typically shifts into OD about 59MPH and tach goes down to 1700 rpm & is much quieter. It stayed at 2300 rpms at all speeds above 50mph and nothing I could do would get it into OD. Had to drive about 125 miles like this to get home. This morning-no ck eng light & no OD shifting problems (just my luck since I took it into the Chevy dealer). Are these 2 quirks connected by any chance? thnx

[DmaxMaverick]

Limp mode, in one form or another. The SES lamp indicates a stored code that can be read, which will tell you why Limp mode was activated. If you were only locked out of OD (with no TC lockup), with the tranny operating normally otherwise, it's possibly only a shift range solenoid error. Most of the time, these are temporary glitches, never to return. It could also indicate a need for a service (fluid and external filter). A shutdown and restart may have cleared the issue at the time it happened (always try this first), and you may have been able to resume normally. In any case, pull the code(s) to determine the cause. If you check with a reader that only indicates P0700, with no other P07xx codes (if you have P0700, there WILL be others), you'll need a reader capable of reading TCM codes (most shops have these). P0700 is a general code, which only requests the PCM activate the SES lamp.

[jsummers72]

the computer says the solenoid b failed. Nothing failed except O/D wouldn't work. Looks like I get off easy. thnx

[DmaxMaverick]

It could be a glitch, or a temporary condition. The electronic/electric tolerances are so critical, it doesn't take much to cause a fit.

With no more than what you've seen thus far, I suggest a tranny service. Better, and what I recommend, is a full flush and fill with a quality synthetic fluid (Mobil 1, Transynd, Amsoil, etc.). The full flush can be done by anyone capable of regular service experience. DO NOT have a shop do a pressure flush, as this can damage the tranny (a warning from Allison). The best method is the easiest, and can be done in your driveway with little fuss.

[JohnC]

If it happens again and you have 125 miles to go, pull over, shut it off and restart it. That may clear the condition enough to get you home.