1996 Cadillac Deville How to do a pressure test?

Transmission problem
1996 Cadillac Deville V8 Front Wheel Drive Automatic

Hi ~ A couple of weeks ago I had a question about our transmission, as we have suddenly lost all gears, but fluid is not burnt. I was told for diagnosis we should first do a transmission fluid line pressure test to see if the pump has output. We are now ready to do that, but need to know three things:
(1) What should the pressure be? (Ie - on the gauge)
(2) What gear do you test it in?
(3) Where do you find the place(s) to connect the pressure gauge to? How many testing ports are there?

Thanks again for your much needed help!
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have the same problem?
Tuesday, June 30th, 2009 AT 9:19 PM

1 Reply

Below is the test procedure, the pressure port is a bit difficult to access. If you look at where the lower trans oil cooler line fitting is on the front, follow straight down 4-5 inches or so and you'll find the 1/8th inch pipe plug, that is the test port. Below I've also included a symptom chart for loss of drive and loss of reverse.

Line Pressure Check
Line pressures are calibrated for two sets of gear ranges-Drive-Park-Neutral, and Reverse. This allows the transmission line pressure to be appropriate for different pressure needs in different gear ranges:

Gear Range
Line Pressure Range

Drive, Park or Neutral
Minimum line 50-55 psi, Maximum line 230-250 psi

Minimum line 90 psi, Maximum line 300 psi

Before performing a line pressure check, verify that the pressure control solenoid for the transmission is receiving the correct electrical signal from the vehicle computer:

Hook up the scan tool.
Start the engine and set the parking brake.
Caution: Keep the brakes applied at all times in order to prevent unexpected vehicle motion. Personal injury may result if the vehicle moves unexpectedly.

Check for a P0748 malfunction code from the pressure control solenoid of the stored transmission. Check for other malfunction codes.
Repair the vehicle if necessary. Include the following areas:
" Inspect the fluid level

" Inspect the manual linkage at the transmission

" Install the line pressure gage.

Put the gear selector in Park and set the parking brake.
Start the engine and allow the engine to warm up at idle.
Enter the diagnostics routine and select MISC TESTS.
Increase the transmission fluid pressure by commanding low amperage. Read the corresponding line pressure on the pressure gage.
Compare your data to the Drive-Park-Neutral line pressure chart below. This line pressure is valid for PC solenoid overrides with the vehicle stopped at idle and in Park-Neutral.
If your pressure readings differ greatly from the line pressure chart, refer to Symptom Tables.

Loss of Drive

Channel Plates

Drive and Driven Sprockets

Drive Link Assembly

Driven Sprocket Support
Damaged, porosity, leaking

Final Drive
Damaged, splines worn

Final Drive Pinions
" Spalled pins or pinions

" Lack of lube

Forward/Coast Clutch Support
No lube

Forward Sprag Clutch
Worn, broken or locked


Manual Valve and Link
Not attached to detent lever

Pump Shaft

Scavenge Pipe Seal
Damaged or missing

Scavenger, Primary Pumps
Seized, broken pump gears

Torque Converter
" Broken lug, failed lug weld

" Sheared lug bolts

" Worn turbine shaft splines

" Low fluid

" Pump hub cracked or broken

" Internal failure

" Closure weld failure

" Cover cracked at weld

Turbine Shaft
Dislodged, stripped splines

No Reverse

Case Cover

Case Cover Gaskets
Damaged or displaced

Checkball in Piston

Driven Sprocket Support
" Porosity or broken

" Feed holes blocked

Driven Sprocket Support Bolts
Loose, not in grooves, mislocated

Driven Sprocket Support Seals

Fluid Pressure
Too low

Lo/Reverse Anchor Pin
Anchor pin broken or not positioned

Reaction Carrier Shell
Missing, teeth damaged

Reverse Band
Broken, worn not anchored

Reverse Band Apply Pin
" Too short or binding in case

" Broken

Reverse Clutch Fiber Plates
Splines or friction material worn

Reverse Clutch Housing

Reverse Clutch Piston
Binding in case

Reverse Clutch Piston Seals
Leaking, damaged or worn

Reverse Clutch Spring Assembly

Reverse Clutch Steel Plates
Splines worn

Reverse Servo Piston
" Bad seal

" Damaged housing

Snap Ring
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Tuesday, June 30th, 2009 AT 11:03 PM

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