BlackRX300

Will a bad knock sensor cause the car to NOT shift into over drive?
Mechanic says codes show bad knock sensor and oxygen sensor, also bank 1 & 2 lean.
I just had a vacuum leak fixed and the car did not have this problem before. Although the check engine, VSC and Trac Off lights were all on, the car seemed to run just fine.
If it was not for the lights being on, I wouldn't even have known there was a problem.
Now the car kinda jerks and runs around 4k rpm's on the interstate and will not shift into over drive.

My dad thinks I have a transmission problem. I thought replacing the bad knock sensor and o2 sensor will correct the shifting into over drive and smooth out the drive.

Any help is greatly appreciated.

hypervish

A bad knock sensor will lock out 4th gear. You could try the knock sensor hack (there's a DIY here somewhere).

BlackRX300

Thanks

I just read about the wiring hack.
Just wanted to make sure I would recover overdrive after the fix.

Drcoffee

Wait a minute. You just had a vacuum leak fixed and the codes now popped up? Have you replaced your pcv valve lately? The vacuum leak was possibly helping the clogged pcv. You may want to disconnect the battery to reset the computer. Also check the MAF as it affects AFR and transmission shifting.

BlackRX300

Yes, something behind the intake was the culprit for the vacuum leak.
The mechanic that has the car now has replaced the MAF with a tested used one. He said it helped the engine run smoother, but the transmission still does not shift into over drive.
I'll tell him to replace the PCV valve.

The codes were reset and still no over drive.

Drcoffee

resetting the codes is not the same thing as disconnecting the battery. Your ecm learns your driving style and and holds the memory for the last 40 or so startups. Until you drain the ecm of juice and start it fresh again, its still trying to run the engine with a vacuum leak. if you take off the negative battery wire and press the brake pedal a few times to suck off any juice left in the capacitors, the computer will start fresh.

BlackRX300

Do you think this will fix the shifting into overdrive?

I'm willing to try anything at this point Beats spending $1200 to have the knock sensor and o2 sensor replaced.

maxSteel

With the CEL illuminated and depending on the codes the car may go into limp mode and lock out overdrive.

After a reset many of the emissions related codes will not immediately return. There is a defined series of stages like "car must run at various speeds for X time".
While the CEL is off your overdrive should start working again.
If you have no CEL and no overdrive (and you didn't accidentally press the OD off button, right?) then I don't know what the cause is.

You should always clear codes and check the first reported code anyway. The others may be a side effect of the first.

carguy07

...This...

Tymiles1

Thank you for attention to detail.