Recently rebuilt my 1999 4l80e installed now in 2nd gear. (Limp Mode) Basically stock, better clutches but stock.
All new connectors, new interior harness, new solenoids (GM) new speed sensors. I understand that if limp mode happens, its more times than others, electrical. Checked voltage at connector, 12V when running. No codes, OBDII is indicating that trans
is in 1st but it is not. you can watch the ecm tell it to shift etc but it will not shift. no metal in pan, fluid clean, no smell.
My question is am I missing a ground somewhere. the ground into the trans indicates connected via Ohm meter. Stupid question, What am I missing. I can get another ECM but that may be throwing money at it and not fix it.
Can someone help.
Thanks

 

I've had this happen multiple times. Multimeter shows 12v, but it can't carry ANY load...easily remedied by replacing the ignition switch.
All power for trans runs through the ignition switch.

 

So are all the solenoids must have 12v to operate?

 

Your vehicle can't get enough amperage past the ignition switch to fully power the solenoids. You need volts and amps to perform useful work. In other words, volts x amps equals watts . . . otherwise known as power or the ability to perform useful work.

Rick

 

Yes the transmission fuse is a 10amp. It must be able to supply the proper amperage to PIN "E" 1 strand will show 12V, but will not supply 10 amps. I rigged up a 9005 headlamp to pin "E" of an old harness. I have plugged it in and the vehicle won't light it up. Then I know that the ignition switch like @MaroonMonsterLS1 stated is usually the culprit.

 

ok great info
i will try that
Thank you

 

Absolutely so. This was such a common problem on all the 99-02 trucks/ suvs that there was a TSB on it. The 2003+ didn't seem to experience this as the electronics and switch were completely different.

 

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Still limping Second gear ?
It's been a year and a half, did ya FIX it ?