I have a 1991 Jeep Cherokee Laredo H.O. with an automatic transmission in it, the transmission seems to be starting in second gear when at a complete stop and it has no power off the line, but when i put it down into 1-2 gear it works fine and has plenty of power, it also doesnt downshift when i put the petal to the floor, i have changed the throttle postioning sensor, adjusted the tv linkage and even tried another transmission control unit, none of these worked...... any ideas
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- Thread starter jeepz
- Start date
lawsoncl
NAXJA Forum User
- Location
- North Idaho
Have you made sure you have power to the TCU? No power to the TCU gives you 4th gear in (D), 3rd in (3), and 1st in (1-2). Also check the resistance of the solenoids. A quick search on "AW4 solenoid test" should get you more info an pins to measure.
i havent checked the power to the tcu yet but this weekend i took the valve body cover off tested all 3 soleniods they were good but i replaced them anyways along with the whole valve body from an aw4 transmission that i got for $150, and the problem still occurs, i dont know what to do at this point......how do u check the power to the tcu and what causes it not to have power how do i fix this?
jeepdude10000
NAXJA Forum User
- Location
- LaLa land!
jeepz said:
in the fuse box check the fuse, and the tcu should be under pass side , and FYI the AW4 is an electronic tranny.
lawsoncl
NAXJA Forum User
- Location
- North Idaho
Here's a list of things to check on the TCU connector while plugged in, you've got the ignition on (engine running shouldn't matter), and shifter in park.
+12 volts on D14, red wire
+12 volts on D16. yellow wire
Good ground on D7, black wire with tan stripe
C14, 15, and 16 are the solenoid outputs. Sitting still, you should have power to solenoid 1 only (C16 on the TCU, dark blue with white stripe). If you pull the connector you should have around 11-15 ohms between the solenoid pins in the wiring harness and ground. If not, you've got a bad solenoid or wiring issue. You mentioned that you checked the solenoids in the pan, but checking at the TCU connector also verifies the wiring between the TCU and the solenoids. Current draw on the solenoids should be around 1 amp, btw.
There is a fuse in the TCU harness under the dash that sometimes pops. I don't recall for sure, but I think it's on the yellow power wire.
+12 volts on D14, red wire
+12 volts on D16. yellow wire
Good ground on D7, black wire with tan stripe
C14, 15, and 16 are the solenoid outputs. Sitting still, you should have power to solenoid 1 only (C16 on the TCU, dark blue with white stripe). If you pull the connector you should have around 11-15 ohms between the solenoid pins in the wiring harness and ground. If not, you've got a bad solenoid or wiring issue. You mentioned that you checked the solenoids in the pan, but checking at the TCU connector also verifies the wiring between the TCU and the solenoids. Current draw on the solenoids should be around 1 amp, btw.
There is a fuse in the TCU harness under the dash that sometimes pops. I don't recall for sure, but I think it's on the yellow power wire.
Hugh
NAXJA Forum User
- Location
- Sutherlin OR
Type in your search window: AW4 Jeep Diagnoses Shift Pointers Wayne Colonna. This will bring up a site with definitive (4 Pages) instructions on checking electronics on the AW4. Very specific on test of TCU. I had same problem as your having. All tests run on TCU were OK so I knew I had a bad wire somewhere. Turned out I had a broken wire that was only intermittently sending 12v to TCU.