Unusual problem

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  #1  
Old 10-19-10, 07:09 AM
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Unusual problem

1997 Buick Century. On two occasions the transmission downshifted to either low or second gear and the speedometer went to zero mph. I was on level ground and at a slow speed. Both times I went approximately 1 city block and the transmission shifted to drive and the speedometer started working. Any ideas?
 
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Old 10-19-10, 07:54 AM
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Well, the vehicle speed sensor (VSS) or its circuit would be a prime suspect I would think; it sends signals for both tranny operation and speedo indicator.
 
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Old 10-19-10, 09:37 AM
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Thanks tow guy I'll check it out.
 
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Old 10-19-10, 10:04 AM
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Could very well be as tow guy stated. Still it would be a good idea for you to scan the TCM (Transmission Control Module), and post any stored coded you find.

Whatís the mileage on the car?Has any transmission work ever been done?

Has a flush job ever been done? BTW, Donít ever have one done.

Whatís the color and condition of the fluid?

Is the fluid reddish/pink or burnt brown?

Has the fluid and filter screen been changed recently?

Drop the transmission pan and tell us if you see a high concentration of metal particles or pieces of metal stuck to the magnets.
 
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Old 10-19-10, 11:05 AM
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Hi, the car has around 150,000 miles. The transmission was overhauled exactly 1 year ago almost to the day. I haven't checked for codes but will. I'm a little surprised I didn't get a check engine light. Seems I never get a problem like 'won't start'. I get weird crap. And somehow weird equals money.
 
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Old 10-19-10, 01:18 PM
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Yours sounds like a common issue that plagues any chain driven front wheel drive transaxle. The models are, T-440 or the T-125C. The 440 is a computerized 4 speed automatic overdrive with a lock up torque converter. The 125C is a 3 speed automatic without overdrive, but still has lock up. All use chains, and as the chains stretch the first thing you notice is slippage.

(Quote) I'm a little surprised I didn't get a check engine light.

Thatís because you thinking of PCM or ECM codes. (In other words engine codes)

Iím talking about TCM codes. (Transmission Control Module) error codes.

Have a scan done at a professional transmission shop and post any codes.

However, before you do that, answer the questions that continue to go unanswered, as answering them may shed some new light on the issue.
 
  #7  
Old 10-19-10, 01:33 PM
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I've taken the car to the shop so I am unable to answer about the color of the fluid. The fluid and filter was changed at the time of overhaul. I'll post back the results of the scans. Thanks so much.
 
  #8  
Old 10-19-10, 04:09 PM
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One small detail to shed some light....Speedo went to zero....Is that it? anything else you noted, ( Radio Blanked out, Clock reset, Heater didnt blow)...

Check engine lights are tricky sometimes.....Obviously there is a malfunction, because the car did something abnormal.......
BUT.....
Just for giggles.....shut the key off at 50MPH, The engine stops, the guages drop out, and You coast to a stop. Now, that wont set a code...The engine shut off ...not because you turned the key off.. but because you interuppted the power supply to the controller. or distributor, or whatever you have... to control ignition.
ow...lets assume a fuse blew for ....Ummm... ok PCM... Very much the same as turning off the key, power to the controller has been interrupted. The controller doesnt know the difference between key off, and blown fuse, so he doesnt recognize this as a problem.......Therefore, no Check engine lamp, no codes, no problem....
Think of your car as a toddler...he only thinks about what he knows....and until he knows that "BELCHING" at the dinner table is a problem, He doesnt recognize the need to cease such activity.
 
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Old 10-20-10, 07:02 AM
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Okay thanks to all of your for your help and suggestions. It turned out to be the speed sensor. I had it replaced and all seems to be okay for now. I would still rather need a tow truck than have an intermittent problem.
 
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Old 10-20-10, 11:43 AM
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(Quote) It turned out to be the speed sensor.

The family of GM vehicle you're driving had a high failure rate of vehicle speed sensors. Years ago GM issued a bulletin/TSB for an updated VSS. You should check with the shop that just changed the VSS, to be sure they used the new updated VSS.
 
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Old 10-20-10, 12:46 PM
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Thanks again ASE MASTER will do.
 
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Old 10-21-10, 10:05 AM
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And another home run for the tow guy.
 
  #13  
Old 10-22-10, 01:59 PM
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tow guy you are right. You hit it out of the park.
 
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