Automatic Transmision AW4
Anthony Dalton
Index :
Section 1 : Brief description
Section 2 : Diagnosing problems
Section 3 : Trouble shooting
Brief description
The AW4 transmission is a 4 speed electronically controlled automatic transmission , the running gear consists of a lock up convertor , oil pump , three planetary gear sets, brake and clutch units, hydraulic accumalators, valve body (With electric solonoids) and a TCU.
the transmission has six shift positions, Park, Reverse and neutral are mechanically operated whilst 1-2 , 3 and "D" are electronically controlled.
The AW4 is controlled electronically in the forward gears by a TCU (Transmission control unit) Also helping to control the transmission are valve body solenoids and sensors that detect speed, throttle opening, gear shift position and brake pedal movement.
The TCU calculates shift and convertor lock up using information provided by the sensors.
There are 2 shift modes programmed into the TCU, Theese are "Comfort" and "Power" . the power mode provides higher engine speeds before the TCU shifts up a gear and will kick down earlier. From 92 onwards this switch was removed and the TCU operated in Power mode all of the time.
Diagnosis
If you have access to a DRB II tester then you can test for transmission faults using this.
If not here are some check / adjustments and tests to try.
1) Check and adjust shift linkage
2) Check engine throttle by looking at the injector throttlr plate movement whilst an assistant presses the accelorator to the floor. Adjust linkage if throttle plate does not open right up.
3) Check transmission fluid when it is at normal running temperature and after shifting through all the gears then back to neutral.
4) Check TPS Adjustment
To find out if a problem is mechanical or electrical :
1) Disconnect the TCU or the TCU fuse
2) Road test vehicle, the transmission should shift as follows
a) Locked in Park
b) back up in reverse
c) not move in neutral
d) 1st gear ONLY in 1-2 position
e) 3rd gear ONLY in position 3
f) Overdrive 4th in "D" position
IF and ONLY IF the transmission performed as above the continue with step 3
IF it was difficult to tell the difference between gears or would not back up go to "Trouble shooting "
Step 3) manuall shift (Whilst driving) From "D" through the gears to 1-2 position and then back up to "D" again. If all seems well you need to test stall, time lag and pressure tests.
"Stall Teast"
this checks the holding ability of the clutches and brakes and of the convertor stator clutch.
Connect a Tachometer to engine.
with engine at normal operating temperature , Apply parking brake and block wheels, in 2wd High position put transmission into "D" NOTE DO NOT LET ANY ONE STAND IN FRONT OF CAR !!!! whilst pressing down firmly on foot brake press accelerator to the floor and note max engine revs. should be 2100 to 2400.
DO NOT keep throttle open for more than 5 seconds.
wait for 1-2 minutes for transmission fluid to cool and perform same test in reverse. Again should be 2100-2400 revs.
If engine RPM is lower than 2100 in "D" and "R"then problem could be
engine output/performance is lacking
stator clutch in convertor not holding
If engine RPM was lower than 2100 in "D" then problem could be
line pressure low
forward clutch slipping
overdrive (one way) clutch not holding
No:2 one way clutch not holding
If RPM was higher than 2400 in "R" then problem could be
line pressure low
direct clutch slipping
1st/reverse brake slipping
overdrive (one way) clutch not holding
If RPM was higher than 2400 in "D" and "R" then problem could be
low fluid level
line pressure low
overdrive (One way) clutch not holding
TIME LAG TEST
this will check the condition of O/D clutch forward clutch , rear clutch and 1st/reverse brake
with parking brake on and transmission at normal operating temperature and A/C tuned off
start engine and let idle in "N"
shift into "D" and time how long it takes to engage gear
repeat twice more
perform same check in reverse
"D" should engage in a maximum of 1.2 seconds
"R" should engage in a maximum of 1.5 seconds
if it took longer than 1.2 seconds for "D" to engage then problem could be
Shift linkage needs adjustment
line pressur low
forward clutch worn
O/D clutch worn
if it took longer than 1.5 seconds for "R" to engage then problem could be
Shift linkage needs adjustment
line pressure low
direct clutch worn
1st/reverse brake worn
O/D clutch worn
PRESSURE TEST
you will need a pressure test gauge (with capacity of at least 300 psi for safety reasons) connected to test port on right hand side of transmission. (use adapter no: 7554 to connect gauge to tranny)
1) bring transsmision to normal temperature and block wheels and apply brakes.
2) with engine idling and transmission in "D" pressure should be 53-61 psi
3) put accelerator to floor (MAXIMUM OF 5 SECONDS) pressure should be 161-196 psi
4) put transmission into "R" and at idle pressure should be 73-87 psi
5) put accelerator to floor , pressure should be 223-273 psi
If line pressure is not within theese specifications you should adjust line pressure cable and repeat test. sometimes it is not possible to get correct adjustment.
If pressure in "D" and "R" are higher than theese specs probable causes are
line pressure cable loose, worn or needs adjusting
throttle valve , throttle cam sticking
primary regulator valve sticking
If pressure is lower in "D" and "R" then probable causes are same as above +
oil pump gears worn
O/D clutch worn
If pressures are low only in "D" the probable causes are
forward clutch
fluid leaking in D range circuit (usually seals or "O"rings.
TROUBLE SHOOTING
| PROBLEM | PROBABLE CAUSE |
| Tranny fluid dicoloured or smells | Tranny fluid dirty Faulty convertor Faulty Tranny |
| Jeep does not move in any gear | shift linkage adjustment valve body faulty faulty convertor Oil filter blocked Faulty tranny |
| Shift lever in wrong possition | Shift lever adjustment Faulty manual valve |
| Bad gear engagement in all gears | Throttle cable adjustment Faulty valve body Faulty accumalator pistons Faulty Tranny |
| Slow 1-2-3 or 3-od Upshift. 4-3 or 3-2 downshifts and shifting back to 4 or 3 |
Faulty TCU ¨Faulty valve body Faulty solenoid |
| slipping on 1-2 or 2-3 or 3-od or slips / vibrates on take of. | Shift linkage adjustment Faulty valve body Faulty solonoid Faulty Tranny |
| holding to long on 1-2 or 2-3 or 3-od | Shift linkage adjustment Faulty valve body |
| no lock up in 2 or 3 or od | TCU faulty Faulty valve body faulty solonoid faulty tranny |
| Jerky down shift | Throttle cable adjustment Fautly throttle cable faulty accumalator piston faulty valve body faulty tranny |
| not shifting down when coasting | faulty valve body TCU faulty faulty solonoid |
| shifts down late or early when coasting | Throttle cable adjustment faulty valve body faulty solonoid TCU faulty faulty tranny |
| no engine braking in 1 or 2 | faulty solonoid TCU faulty faulty valve body faulty tranny |
| not holding in park | Shift linkage adjustment parking lock cam/spring faulty |