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sprinkles08, ASE Certified Technician
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Isuzu Trooper LS: 2000 isuzu trooper AT wont shift out of first

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2000 isuzu trooper AT wont shift out of first gear. Had an accumulator leak, which is now repaired. May have been run low on ATF too many times. Pulled pan, replaced filter, and refilled with ATF. Still wont shift out of first. Wont start in winter mode. No MILs.

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Even though the engine light hasn't come on I would still recommend seeing if there are any fault codes stored. It's possible that an electrical issue could be preventing the 1-2 shift and there would most often be a fault code stored. It may be a solenoid or solenoid wiring issue. You may opt to replace the solenoid and see what happens (solenoid A on the valve body).


If it's not a solenoid/wiring/controller issue then it's going to be an internal trans issue. It could be a failed clutch or it could be a geartrain component. If a clutch fails it will usually slip first before totally failing and would often cause the fluid to burn, geartrain failures are usually sudden.

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Customer: replied 3 years ago.



Thank you for your reply.


I found another string below, that speaks specifically about solenoid A (1-2/3-4 shift) and B (2-3 shift). The transmission won't shift from 1-2, suggesting that A is not functioning. Furthermore, it wont start in winter mode (3rd) gear, suggesting that solenoid B doesn't work. However, reverse functions (solenoid B). Does this point to something besides the shift solenoids?


Also, I rechecked for codes using my code reader. There were none. Are there deeper codes that I cannot read with a simple OBD II reader?


Because the accumulator cover was leaking copious amounts of ATF for several months, I thought that some of the electrical connectors might be fouled. I cleaned a 3-4 pin connector on the bottom of the transmission. Do you know where the connector is located that is referenced below (pin 6- I assume it has at least 6 pins)?


I need to drop the pan to get to the solenoids on the valve body, correct?


Thank you for your help.


Below is the link and referenced string.


Gear selection is accomplished by switching two shift solenoids On or Off as necessary to select the correct gear. The two solenoids are controlled by the PCM using wires that go through the harness that apparently got melted. Since Winter Mode (3rd gear) can be selected, the 1-2/3-4 (Shift A) solenoid is working. The 2-3 (Shift B) solenoid is apparently not working due to a defective solenoid or a wiring problem in the harness or a problem in the PCM.

The solenoid is energized when the PCM provides a ground on the control side the selected solenoid. The +12 VDC power side of the two solenoids are connected together inside the transmission, so if Shift A has power so does Shift B. Shift B is energized in P,N,R and 1st and 2nd gear. The Shift B control is on Pin A (6) of the 7 Pin connector. If Shift B is not selected, such as in Winter Mode, the voltage level on Pin A (6) will be +12 VDC, When Shift B is energized Pin A (6) will be 0 VDC.

If the voltage on Pin A (6) remains +12 VDC when it should be 0 VDC the problem is in the PCM or the wiring to the PCM.
If the voltage on Pin A (6) remains 0 VDC when it should be +12 VDC the problem is a defective solenoid (open coil).
The engine needs to be running when making voltage checks.
It is also remotely possible the the Shift B solenoid is working properly but another defect is causing the problem.

If you've checked with a code reader and found no codes then that should be enough.

Solenoid B is a normally open solenoid which means it flows fluid through it when turned off, it blocks fluid when turned on. For third gear solenoid B is turned off to allow flow, so if the solenoid wasn't working you would still have third gear as long as A and the rest of the trans are working correctly. Solenoid A is turned on for third, so if solenoid A isn't working then it's not going to allow third gear. Since you do have first gear and first requires solenoid B I believe we can rule it out.

The connector we're concerned with is a 7 way connector, connector M7 on the left side of the trans. The other large connector is from the range sensor/neutral safety switch, which is mounted to the left side of the case.

Yes, you do need to drop the pan to access the solenoids on the valve body.
Customer: replied 3 years ago.

Thank you very much. Excellent advise!

You're welcome and good luck!

Customer: replied 3 years ago.



I replaced solenoid A, replenished the fluid, and tested the operation of the transmission with my car on jacks. Reverse works as before. The rear wheels spin in 1st through 4th, but the transmission is locked in first gear - no shift from 1st to 2nd, 2nd to 3rd, or 3rd to 4th. Interestingly, the rear wheels spin in winter mode, which it did not do before; however, it appears to start in 1st gear in the winter mode and not 3rd as designed. The questions I have are as follows:


  • Will the transmission shift through the gears while the car is still on jacks and without a load on the wheels, or do I need to road test the car to test the operation of the transmission through the gears?

  • If there still is no shift with the solenoids operating properly, can I assume that there is a deeper transmission problem, i.e., one that requires a transmission overhaul?

  • This is just speculation, but what do you think the failed component(s) is (are)?


If the transmission needs to be rebuilt, I am thinking about doing it myself. I have a reasonable mechanical aptitude, but I have never tackled an automatic transmission. Would you recommend it?


Thank you,



It should shift on the jack stands but you might give it a quick spin on the road to see if it shifts. MOst likely it won't.

Is it still not setting any codes?

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