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5th Gear Slips


I have a 2002 Hyundai Sonata V6 with around 257,000 miles on it.

Recently, it has been slipping out of 5th in automatic mode so I have been driving it in manual mode without utilizing the 5th gear. When I’m in 4th, the RPMs are around 2,200 so not that bad going 60 mph.

The first event was when I was accelerating onto the highway on a bridge going 65 mph and all of a sudden, felt a thud in the front end and the “check engine light” came on. I also noticed that the RPMs were registering way too high (way over 3,000k) so basically it sounded like I was going 65 mph in 3rd gear. I had to drive until the end of the bridge, pulled over and shut off the car. Once I started it, no problems driving in 5th gear for the next 45 minutes.

Error codes were P1790 and P1529.

Added a bit more ATF fluid since it seemed low, the “check engine light” turned itself off. I drove at 65 mph for about 45 minutes and felt the front end dip again as the tranny slipped into the 3rd gear. Again, I had to pull over, shut off the engine and turn it back on again.

Because I don’t really have the funds for another car at the moment, I have been driving it in 4th gear with a top speed of around 60 mph. The “check engine light” turned off after the last slip, but I have been receiving so many opinions.

I’m pretty sure the transmission is going out :frowning:

You could drive 60 mph at 2200 rpm forever and not hurt the engine. As Click and Clack would say, “Now is the time for a scientific experiment. (How long can the tranny last?)”

You could try draining the fluid and changing the filter.

I agree with changing the filter and ATF, don’t flush, just drain and fill may help, but beyond that, considering the number of miles, I would just start saving for a replacement vehicle.

@insightful‌ Thank you, I have heard that from a bunch of my friends. Better to be in 4th than in the 3rd failsafe mode.

@knfenimore Thank you, that was also another option. We looked at the fluid and although it was not a clean reddish pink, it looked like a lighter shade of brick. Plus I doubt the filter had been changed on this car in a long time.

@keith Thank you. I will definitely look into the cost of a drain and fill and filter change with no flush. And the considering another vehicle is definitely on the horizon. This car definitely has a lot of miles!

P1529 is the TCM asking the ECM to turn on the CEL…(because of P1790, a computer checksum error…) So either the TCM is failing or its instructions to the transmission are not being followed correctly and it’s getting confused…