QuestionI own a '02 Buick Rendevouse Cx with all-wheel and 30k miles on the vehicle and tranny. As soon as I purchased the vehicle, I noticed the transmission was not shifting out of third or into overdrive. I am actually a shop supervisor for Kargo Repair of Indianapolis, And a A.S.E. certified mechanic. I have been in charge of my shop for ten years and recently lost my transmission diagnostic specialist To small cell lung cancer. Anyway ED, through the years I've lost track of modern technology, and I never enjoyed paying people who weren't experts for such thing as the complexities of transmissions.
I'm trying to say I don't kwon WWHAT the problem could be, External, or the dreaded internal!!!!!! I'm trying desperately not to sound ignorant so I apologize Ed, for taking such a small question and creating a monster. PLEASE let me know your opinion on this. I greatly appreciate your valuable time. You're doing a wocerful job here. Thanks again. I will follow up with you as soon as I figure this out(and as long as you don't object)
CHRIS LOWE, BDACAMEL@YAHOO.COM
AnswerChris ,
I'm pretty much in the same boat as you when it comes to modern transmissions and most newer computer controlled systems. My expertise really only goes as far as the late 80's when it comes to diagnosing and fixing automobiles .
Transmissions are a speacialty and even I send my cars off to a qualified transmission mechanic , just because you have general mechanics and then you have transmission technicians.
From what I've dealt with you might want to start off with checking your fluid level and changing the filter first.
Heres an article that will get you started . Chris, I'd take the car to multiple shops and play the field as far as price/diagnosis . I had a Lincoln that fell out of gear , in the middle of the highway . Took the car to two tranny shops and each one told me that the tranny was done for . Come to realize that the Jiffy Lube guy forgot to put the last two quarts of tranny flud in ;) Lazy me right
Heres the article :
Transmission:
The normal automatic transmission is fully automatic with four forward and one reverse speed. It consists of a lockup torque converter assembly and a three unit planetary gear train. Electronic controls for the transmission are integrated into the on-board Powertrain Management systems. Sensors provide inputs to the Powertrain Control Module (PCM). The PCM electronically controls the transmission hydraulic system for gear selection and automatic shift control. Torque converter operation is controlled by the PCM. These controls, along with hydraulic controls in the main control body, operate a piston plate clutch in the torque converter that eliminates torque converter slip when applied.
Testing:
There are several ways to test an automatic transmission. There are some that can only be done by a shop that has the proper equipment, and others you can do at home.
• Air Pressure Tests
To test the bands and servos inside the transmission, air pressure can be substituted for fluid pressure. When compressed air is applied to certain ports, it will apply the particular band or servo. When a band or clutch engages a dull thud will be heard. There should be no hissing heard while band or servo is engaged. This can only be done by a repair shop.
• Line Pressure Test
Transmissions need to operate with the proper fluid pressure. If the fluid pressure is too low or too high, shifting can be too soft or too hard. Different parts of the transmission operate with different fluid pressures and a transmission pressure gauge can be attached to a transmission to check these pressures. These readings can be compared to a chart that will pinpoint the most likely cause of a problem.
• Shift Point Road Tests
Each shift in a transmission is supposed to occur at a specific time under certain throttle conditions. For example under light throttle a 1-2 shift will take place sooner then a 1-2 shift under heavy throttle. By knowing when the shifts take place and when they are supposed to take place you can figure out what is wrong with it.
Transmission Fluid Leak Tests
This one is kind of self-explanatory. You can use a special dye to find a transmission leak. Oil-soluble aniline or fluorescent dyes premixed at the rate of one half teaspoon of dye powder to one half pint of transmission fluid may be useful in locating the source of a leakage. If the transmission fluid in the radiator cooler leaks into the coolant system, a black light must be used to see the fluorescent dye solution. Fortunately there are not too many places an automatic transmission can leak. To do a through check:
Check speedometer cable connector at the transmission. Replace rubber 0-ring, if necessary.
Check oil pan gasket. Tighten attaching bolts to proper torque and/or replace gasket, if necessary.
Check fluid filler tube connection at transmission case. Check filler tube 0-ring seal for damage. If leakage is found, install new short oil inlet tube and 0-ring seal or clean the area and apply sealer around the tube.
Check fluid lines and fitting between transmission and cooler in radiator tank for looseness, wear, or damage. If leakage is found, tighten fitting to proper torque, or replace the damaged parts.
Check engine coolant in radiator. If transmission fluid is present in coolant, the cooler in the radiator is leaking.
If leakage is found at the downshift control lever and manual lever shaft, replace seal.
Inspect pipe plug on left rear side of transmission case. Tighten plug or replace, if necessary.
Fluid leakage from the converter housing may be caused by engine oil leakage past the rear main bearing, by oil galley plug leaks, or by power steering fluid leakage from steering system. Determine the exact cause of the leak before beginning service procedures.
If you have leakage from the converter housing, here's what you can do to isolate the cause:
Fluid leaking by the front pump seal lip will tend to move along the impeller hub and onto the back of the impeller housing.
Fluid leakage by the outside diameter of the seal and front pump body will follow the same path as the leaks from the front pump seal.
Fluid that leaks from a front pump-to-case bolt will be deposited on the inside of the converter housing only. Fluid will not be deposited on the back of the converter.
Leakage by the front pump-to-case gasket may cause fluid to seep down between the front of the case and converter housing.
Fluid leakage from the converter-to-flywheel stud weld will appear at the outside diameter of the converter on the back face of the flywheel, and in the converter housing only near the flywheel.
The following areas of possible leakage should be checked to determine if engine oil is leaking.
Leakage at the rocker arm cover may allow oil to flow over the converter housing and cylinder block, causing oil to be present in or at the bottom of the converter housing and cylinder block, causing oil to appear at the bottom of the converter housing.
Oil galley plug leaks will allow oil to flow down the rear face of the block to the bottom of the converter housing.
Leakage by the crankshaft seal will work back to the flywheel, then into the converter housing.
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Some common problems :
No 4-3 Downshift
1.Faulty Powertrain Control Module (PCM) sensor inputs/outputs.
2.Fault in vehicle wiring harness.
No 3-4 Upshift
1.Improper band/clutch application pressure.
2.Main control assembly gaskets damaged or bolt out of torque.
3.Main control separator plate damaged.
4.Main control solenoid stuck or damaged.
5.Overdrive planet assembly damaged.
6.Overdrive band adjustment incorrect.
7.Overdrive band friction elements burnt or missing.
8.Overdrive band cylinder damaged.
Chris if you have any more questions please feel free to ask . Don't forget to rate my response to you .
Cheers,
Ed McKenna
