The check engine light came on in my 03 Yukon. We took it to an auto parts store and they did not give me the code but said it was a vacuum leak, probably from the gas cap.
I checked the cap (it was fine), and the code went away. We drove about 40 miles, then parked the truck for about an hour. When I started it back up and put in reverse, it would not back up and acted like it was in neutral. I had the wife put it in neutral and pushed the truck back a few feet. My wife was then able to put it in reverse and it would back up, but it made a loud thumping sound while backing up, and also made the thumping sound while putting it in drive and moving forward.
We had it towed and the next morning the problem seemed to go away. (It would go forward and reverse with no issues).
I took it to a mechanic and after a day he told me the transmission is done and should be replaced. I told him I would think about it. After sitting at the shop for a few days I went to pickup the vehicle and drove it home with no problems.
1. Could a vacuum leak cause transmission or shifting problems?
2. How does one diagnose an intermittent problem like this one?
On an unrelated note I checked the transmission fluid, and it is full and does not have a burnt smell. I'm sure I should have changed it, but at this point I think we are past a "transmission flush" fixing this problem. The Yukon has almost 200k miles on it, and does have some other issues so I'm debating on putting a used or new transmission in the vehicle. Thank you for the help.
I checked the cap (it was fine), and the code went away. We drove about 40 miles, then parked the truck for about an hour. When I started it back up and put in reverse, it would not back up and acted like it was in neutral. I had the wife put it in neutral and pushed the truck back a few feet. My wife was then able to put it in reverse and it would back up, but it made a loud thumping sound while backing up, and also made the thumping sound while putting it in drive and moving forward.
We had it towed and the next morning the problem seemed to go away. (It would go forward and reverse with no issues).
I took it to a mechanic and after a day he told me the transmission is done and should be replaced. I told him I would think about it. After sitting at the shop for a few days I went to pickup the vehicle and drove it home with no problems.
1. Could a vacuum leak cause transmission or shifting problems?
2. How does one diagnose an intermittent problem like this one?
On an unrelated note I checked the transmission fluid, and it is full and does not have a burnt smell. I'm sure I should have changed it, but at this point I think we are past a "transmission flush" fixing this problem. The Yukon has almost 200k miles on it, and does have some other issues so I'm debating on putting a used or new transmission in the vehicle. Thank you for the help.
