Automatic Transmission

Hi there,

I just changed the Automatic Transmission fluid for my 1999 Infiniti QX4, and the car got into a problem: the transmission run only on 3 gears, instead of 4, and it shifts at a very high rpm (4000-5000) and very rough. I checked with my brother, a backyard mechanic, and he suggested me to replace the filter (which I didn’t do at first) so I replaced the filter and filled with new fluid again, but the problem still there. Before the change, the QX4 was running fine and the mileage is about 162,000. This is the first transmission fluid change.

Do you have any idea why this fluid changed creates this problem?

thank you very much.

Hung Vu

Where did you get the new fluid? Are you sure it is the proper fluid for your car’s transmission? Any ordinary generic auto trans fluid doesn’t cut it with modern auto transmissions.

How did you change the fluid? Did you drop the pan? Did you “flush” the old transmission fluid out? Since the trans with 162K miles on it has never been serviced for a fluid change, it was way, waaaaay overdue. This means extra junk, gunk, and debris has built up in the transmission over the years. Changing the fluid could dislodge some dirt and gunk and it is clogging passages in the transmission body or clutches.

Why would you go through the effort to change the fluid and not change the filter? This just doesn’t make sense, pennywise and pound foolish. Dirt from the old filter could be dislodged and find a way to do damage.

At this point I think you have a pretty serious, if not fatal, transmission problem. Time to get someone who specializes in auto transmissions to step up and get involved.

Some Honda’s require a very specific tranny fluid. Did you use the Honda Approved fluid for this vehicle. You don’t have to get it from Honda…just make sure it’s designed for Honda transmissions.

You didn’t overfill the transmission, did you? You are supposed to check the fluid level of most automatic transmissions while they are hot from use and in neutral or park with the engine running.

If you just did your first transmission fluid change at 162,000 miles, there is a good chance your transmission is failing because of neglect, but it is happening now coincidentally.

Mike, does Honda own Infinity? I knew they owned Acura, but not Infinity.

I have no idea why I was thinking Infinity…

Yes Honda Owns Acura…and Nissan owns Infinity.

I’m with Whitey on the probability that this is merely a coincidence.
When transmission fluid is not changed every 3 yrs/30,000 miles, you can anticipate transmission failure anytime after 90,000 miles.

Truthfully, I am very surprised that the vehicle made it to 162,000 miles before the transmission began exhibiting these symptoms. Just chalk it up to a total lack of transmission maintenance for the preceding 10 years.

Scan the computer for any codes…


First, thank you for all of your responses to my question and sorry for taking so long to reply to your help.
The problem from my 99 QX4 auto transmission is not from the transmission itself after I changed the fluid, although it sound just like you guy described it, but rather, it’s from the “Position Throttle Sensor (module)” locate near the air intake and Idol cable (after the Air Mass Sensor). No body can refer to this module because I didn’t tell the whole story: I washed my engine after the oil and fluid changed, and the water get into that module that caused the module shorted circuit. It’s very surprised me too when I brought it to the Infinity dealer for a diagnostic and they asked me, have I wash my engine…
The car is running fine after they replaced the module and I just want to share this information with you guy.
Thanks again,
Hung Vu
ps: I have another question with my 300ZX which I’ll post it on after this.

Glad you got it fixed. The TPS tells the computer what position the accelerator is in which, amongst other things tells the transmission when to shift. What you had, I have seen quite a few times and I recently dug out a scanner snapshot of this very problem which I will post. In the pic below look at the PID on the bottom labeled TPS. Notice the spikes where it maxes out at 4.94v?? This is a faulty TPS. Notice the spikes at 350 and 450? the vehicle was sitting in a driveway in Park and just idling when this happened. When these spikes happened while driving it caused the transmission to shift at the high rpm’s and caused the trans to fall out of overdrive and cause the tcc to remain unlocked not to mention horrible gas mileage. Glad your QX4 is running right again.


Sorry for the blurry pic, it seems that cartalk reduced the size of the pic.


Thanks, transman.