Trans slipping in 1st; can VSS be bad if odometer is working?

[Scott-Ohio]

I have a `97 Lumina (3.1) with 4-spd AT (4T60-E) and although it seems like I'm slipping in 1st (sluggish starting off from stop) I wonder if the Vehicle Speed Sensor (VSS) could be bad. Is it possible for the speedometer to work and still have a bad VSS?

The cruise control rarely works anymore too, so I'm beginning to think the VSS may be the prob.

With 172K miles (90% hwy) I guess I could be worse off and although I'm considering draining trans fluid (7 qts, not complete 11 qt flush) and replacing filter, I'm also wondering if I should capture and re-use the old fluid to avoid risking possible further damage caused by additives/detergents in new fluid--have heard many say serious trans probs appeared shortly after changing fluid in trans with high miles when it has never been chg'd before. I'm mainly considering the drain procedure cuz I'm concerned that the filter may be clogged with sludge and is causing the drag on take-off.

All other functions seem fine--starts right away, good acceleration on hwy, etc...just that real sluggish/dragging feeling taking off from stop, and of course, the lack of cruise control 99 times out of 100 attempts!

I should mention that the cat has checked out to be fine--thanks for the vacuum test tip to diag the cat, jeffco!

Lastly, someone mentioned it may be starting out in 2nd, but all gears appear to be working, including manually selecting each one with gear selector. I do get the OBD-II DTC codes P0751/P0753, but am hoping it's not a sticking solenoid cuz I've been told you might as well rebuild the tranny by the time a tech gets to the solenoid to replace it!

Any thoughts?

[cadgear]

As far as the ODO working when the VSS is not, no. The VSS reports to the PCM and also drives a small electric motor which, after much gearing, drives the ODO display. If the VSS were not working as it should, you'd see screwy mileage, speed, and PCM sensor data (if you hooked it up to a scan tool whilst driving). As far as slipping in first, I don't know much about the beast that is the transaxle, but I do want to know about the CC. Does it not hold a speed at all, or does it catch then immediately release? Check the brake signal switch, a stuck closed signal would kill cruise.

Have you tried various conditions when starting out? i.e., air on, off, punching it, reverse, etc. To truely start out in first, second, third, etc, you'd need a Tech2 or other scan tool to command the transaxle into that gear. Otherwise, simply selecting the gear range via the shifter simply tells the transmission "Hey, don't go higher than this" but you never know what gets told along the way. Solenoids may very well be shot, like I said I'm not totally sure on that.

[jeffcoslacker]

Are you actually slipping (engine speed overrunning for gear range) or just feeling like you are pulling against a load (we used to call it trailer hitching), or like the throttle response is just flat and the motor won't run up?

If you are going about 20 mph, and shift down manually to first with no throttle, it should just about toss you through the windshield on the downshift. Then you know you are in first. Then stop and take off with the shifter in the normal position, and see if you get a normal acceleration.

I have a friend with a Toyota Camry that has been doing what you describe for a long time now. Very flat acceleration, poor mileage. I drove it, and found that it was actually failing to downshift to first, so it starts off in second. If you put the shifter in first from a stop, it makes no difference. But if you force the 2-1 downshift like I described above, it will start off in first after you stop, but only that time. Once it shifts outta first, it misses it again.

I suspect a solenoid problem on it. They're external, gonna check the connections and maybe even tap 'em with a hammer, and see what happens.

When you change your fluid and filter, I'd just go ahead and replace the fluid. I never changed mine until 114,000, and it's been fine. I just advise against flushing and complete fluid exchange at high mileage. It is remotely possible that a sticky valve body could be part of your problem, and the newer fluid may help. With the 7 qt change, you'll still have ~30% old fluid, that should be fine.

[Scott-Ohio]

[quote=cadgear]Does it not hold a speed at all, or does it catch then immediately release? Check the brake signal switch, a stuck closed signal would kill cruise.[quote]

First, I meant to say the "speedometer" works. Yes, the odometer works too. No probs with either

Regarding CC, when it works, it does hold the speed, it just rarely catches at all. When it does, the brake switch or turning off the CC switch on the turn signal switch will terminate CC.

[quote=jeffcoslacker]Are you actually slipping (engine speed overrunning for gear range) or just feeling like you are pulling against a load (we used to call it trailer hitching), or like the throttle response is just flat and the motor won't run up?[quote]

Yes, more like trailer hitching, but only noticed when taking off from a dead stop.

[quote=jeffcoslacker]I suspect a solenoid problem on it. They're external, gonna check the connections and maybe even tap 'em with a hammer, and see what happens.[quote]

Jeffco, do you know where the solenoid(s) is located?

Thanks to both of you for replying--this is starting to drive me nuts!