Engine Light goes on - can not go into 3rd

[jbdkisner]

Friday, I started my car and the engine light came on. When I drove, I can get to about 35 MPH, but then it will not shift to the next gear (3rd?). If I step on the gas, it just revs up. I can get the speed to about 45 MPH, but at 3500 RPM.

I took it to the local auto repair shop and they said the both catalytic converters are clogged and 3 o2 sensors are bad and need to be replaced. I asked if that was the cause of the Tahoe not going into 3rd and their response was, "well, we are not sure until we clear the engine light and the reason for the engine light is the o2 sensors and cat converter."

So.. could the o2 sensor and cat converter be the reason for the Tahoe not going into 3rd? This was all of a sudden. Also, I just has a smog test four months ago and it passed. I would assume if I have faulty cat converters or o2 sensors, I would not pass.

The Tahoe has 148K miles..I do not want to drop $2,000 on the cat converters and o2, just to have the same problem with shifting and a new transmission is warranted.

Another shop I called said that the cat convertor and o2 sensor are completely seperate from each other. Would have no effect.

Thoughts? Thanks.

 

[joshualmarley]

I really don't think they problems are related. There's a "limp" mode where the transmission won't let you out of 2nd. Maybe take it to a transmission shop and have them take a look. FYI. Cats and an O2 sensor shouldn't cost you over a grand installed with labor.

 

[Phillips252]

Don't know what year you have but I had the same problem on my 99' yukon and it was the ignition switch, do all of your Gauges work or just your tach? If just your tach is working I would say it is your ignition switch.

 

[SLCHOE]

Does it lack power also? Clogged cats could cause this only because the engine output would be greatly reduced and sensors the PCM looks at for shifting may never be met under that condition.

Pull both upstream oxygen sensors out of the exhaust piping, leave the harnesses connected and hang them up and away with zip-ties if need be. Take it for a quick drive and see if it acts better. It will be loud but if both cats are clogged this will give the exhaust somewhere to go. If it shifts through all gears, then their diagnosis was correct and you will need new cats. Don't drive it too long if it doesn't act any better because by pulling your O2's you will be in open loop (running rich) and this can damage the cats if driven for long periods of time.