Isuzu SUV Forum banner
1 - 4 of 4 Posts

·
Registered
Joined
·
10 Posts
Discussion Starter · #1 ·
This misfortune is dragging for over two months now and I am getting really frustrated and anxious to figure what it is.

The symptoms are:

  • No gears engage while in auto mode i.e. in 2,3,D
    No blinking or constant warning lights, neither engine nor tranny
    No OBD2 error codes
    Manual L works fine, can be up-shifted all the way to hwy speed as if it was in limp, but again â€" no codes.
    Reverse works Ok
    Fluid level can’t be better - checked many times
    Gear range sensor is good
History:
It hesitated on 2->3 shifts maybe once or twice but barely noticeable, then on another traffic light it just wouldn’t move. No previous history of noises or vibration, nothing.
I dropped the tranny and rebuilt replacing everything but solenoids. On the first test drive the problem seemed to be fixed, only to reappear back the next day.
I replaced the PCM â€" no change.
Made sure battery is fully charged â€" no change.

I got an USB oscilloscope preparing to chase the PCM signals but then read the manual another time and figured that all possible shorts and opens are closely monitored by PCM. Probability of some sensor failure or bad contact with no codes issued is real slim.

So, my thinking is… it drives in manual hence mechanically/hydraulically it is fine. Automatic mode doesn’t work, hence i it must be PCM or electrics downstream. New PCM and no codes means everything tests fine, but not necessarily performs so. First gear in auto is controlled by 2 solenoids (one of which is off) and power motor. The other solenoid is also used in reverse, which works, meaning the solenoid is good (?). It leaves the force motor as the suspect … but then it also used in reverse … at this point I lose it and ran out of any creative ideas.

I would really appreciate any comments or guesses.
 

·
Registered
Joined
·
12,184 Posts
The 1-2/3-4 solenoid is energized for the 1-2 upshift and in 3rd gear. When Winter Mode is selected in D range, the transmission is configured for a 3rd gear start. If the vehicle won't move in Winter Mode it is probable there is a problem involving the 1-2/3-4 solenoid. Reverse is not selected by the shift solenoids, the manual valve controls engagement.
 

·
Registered
Joined
·
10 Posts
Discussion Starter · #3 ·
Thanks Buster. I see, Reverse doesn't need any solenoids activated, I misinterpreted the diagram that shows B (2-3) in On position in P, R and 1st.

The car wouldn't move in 3rd (Winter mode) either, but .... 3rd uses A and B solenoids in opposite states compared to 1st, so how does it isolate the 1-2 (A) as a suspect?
 

·
Registered
Joined
·
10 Posts
Discussion Starter · #4 ·
Just for the future readers reference, the problem was in solenoid A (normally open). Apparently, somewhen, my transmission got overheated and it weakened (softened?) the plastic mount of the valve saddle in the solenoid. The little ball inside wasn’t reaching it’s saddle (or reaching not tight enough). The coil was intact though.

What was happening is the solenoid was testing fine by the PCM (open or shorted circuits tests) and hence there were no codes. When I tested the faulty solenoid during the tranny rebuild, I heard it clicking on the table and concluded it is functional while instead I should have attached a hose or something and blown to test the actual valve and not just the coil&core.

Anyhow, a new solenoid is in and the whole thing is back in action !!! (… so far…)
 
1 - 4 of 4 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top