Question about 2002 Pontiac Grand Prix

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What would cause my transmision to drop to a lower gear between 50 to 62 mph

About 5 months ago I started my car and the speedometer needle pinned all the way to the right. I shut the car off and restarted,every thing was fine. It happened about once a month but I didn't bother with it as I was going to get another car, but plans change. The car is OK in the morning, I can drive about 20 miles before the speedometer needle starts wiggleing and the transmission seems to be searching for the correct gear. I've owned a car that had a slipping transmission, this problem doesn't feel the same, I don't lose speed, just slightly higher engine revs, and a temporary drop to a lower gear. It isn't a constant problem,it will happen and then be normal for 5 or 6 miles.In the morning it happens sooner than 20 miles if I park the car at a store. When the trans problem started I ran a tube to the bottom of the trans pan pumped out some fluid, and added a bottle of lucas treatment [didn't help]. The fluid I pumped out wasn't dark, didn't smell bad and had no particels. A friend who is a hot rodder says I need to put a new trans filter in and a new speed sensor and that will solve the problem. The guy that owns the local transmission shop tells me I need a transmission over haul and that I would be wasting time and money with the new filter and speed sensor.Any ideas on this, thanks

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Your friends comments are good advice, but first did you check the trans fluid level when you checked the condition etc of the fluid ? as low fluid could cause these symtoms,if the level is ok i'd then get the OBD codes read as this will show what sensor/switch may be faulty ie the speed sensor mentioned by your friend but by doing the OBD you will have a diagnostic result,keep me posted

Posted on May 09, 2014

Testimonial: "The level is fine, what would you expect to pay for a code reading at a shop?. Advance auto parts doesn't do diagnostics on a car of my vintage. It's a 1992 chevy lumina 3.1 4 speed. It's high miles but all county driving, constant speed ,very little stop and go. Thanks"

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  • steve May 09, 2014

    ok the original post had it as a 2002 year vehicle, if the level is ok then i'd be looking et the fuel/air system ,these older vehicle dont have such a comprehensive OBD system so i'd log into a chevvy owners forum as these groups will have a wide range of knowledge on these vehicles, a few quick check you can do is look at the pipe work to and from the air intake/filter box for cracks ,splits etc, also the crankcase breather pipe than goes to the rocker cover may be getting to the blocked stage so give that a flush through with some solvent ,run engine in the dark or a closed garage with a pipe on exhaust out side ,dont want to gas yourself,and look to see if there is any arcing across the plug leads , distributor,coil etc , the chevvy forum would be the best place for more involved advice keep me updated and good luck

  • steve May 09, 2014

    your friend s suggestions are also a valid way to procede as wont cost a lot and could well be the solution

  • kevin kelly
    kevin kelly May 09, 2014

    The mechanic that works on my car did do a cheapy fix on the crankcase breather pipe with a rubber hose and a brass fitting to the air intake on the far side of the air filter. Thanks Steve, clean that out.


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Sounds like your having a a computer problem... what year make and model

Posted on May 09, 2014

Testimonial: "Rick when I posted this question i thought I changed the make and model . I guess I didn't It's a 1992 chevy lumina 3.1, 4 speed, thanks"



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Replace the ranny oil, dont flush it just drain it throught the trany oil pan and replace the filter and gasket then refill the tranny with type F oil this should stop the slipping

Posted on Oct 23, 2008

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SOURCE: transmission speedometer problem

This all can be caused by a defective Vehicle Speed sensor, also called a VSS, also run a test on the computer to see if any codes are in memory that will help to sort this problem out.

Posted on Nov 08, 2008

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SOURCE: Engine revving, but car moving slowly until higher gears

Check fluid level and see if it smells burned. If you do not work on it yourself, have a good reliable trans shop check it out. Usually the repair shop you use can recommend which trans shops do good work.

Posted on Apr 14, 2009

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SOURCE: Transmission problem ?

the very 1st thing to do is have the system tested for trouble codes related to the trans problem, u may have a defective trans shift solenoid.

Posted on May 20, 2009

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SOURCE: car losing power for a few minutes then starts running fine. happens often

replace fuel pump relay.if it still loses power. check fuel pump pressure.if all good scan it check for egr valve going bad.

Posted on May 25, 2009

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