99 Isuzu Trooper suddenly not changing gears! No DTC codes!!

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99 Isuzu Trooper suddenly not changing gears! No DTC codes!!

Postby Bahram » Sat Jun 05, 2021 5:15 pm

Hi,
I am new to this forum so please be patient with me.
I got a 99 trooper 3.5 L with a 4L30-E transmission. Just replaced head gaskets myself and engine is running very well.
2 days after the repair I drove it in the city and stopped at a red light. Car was on D at that time and transmission just stayed on 3rd or 4th gear! Manually I can start rolling by putting the car on L and slowly moving up to D just like a manual transmission.
My questions:
1- Can this failure be related to the engine repair?
2- Have anyone experience the same issue?
3- How come I do not any error codes (engine or transmission) and it seems everything is fine with the car?

These are what I have done so far.
I have taken the car to a reputable transmission shop and they confirm it is electrical.
The scan of OBD displayed a whole list of sensor errors due to poor cable harness connection under the hood. Push the connectors back together and remove the battery connection for 1 hour to clear any error codes.
All the codes are gone now and still car wants to start on 3rd or 4th gear!
Winter mode puts the car in 3 and moves forward slowly and it seems the mechanical/hydraulic components are working ok.
Since the problem is electrical, I have checked signals to and from PCM and they are ok according to the service manual.
Solenoid A signal at PCM is always Hi (12.5 V) and solenoid B stay at low in all shift stick positions. (PRND32L). These soleniods suppose the change from hi to lo and low to hi to change the gears based on the position of the shift and vehicle speed.
My understanding:
1- With car on D and speed of zero, tranny should be on 1. My car with the correct signals to the tranny is at 3 or 4!!!!
2- When car accelerates, the A and B solenoids will change modes (on -> off or off -> on) to change the gears according to the driver input and the shift selected. (according to Isuzu service manual section 7A1-8 Gear Shift Control)
I am looking for some tips before I give up on this.
I appreciate in advance,

Regards,

Bahram
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Re: 99 Isuzu Trooper suddenly not changing gears! No DTC cod

Postby Buster28 » Sun Jun 06, 2021 10:33 am

The Shift A solenoid, Shift B solenoid and the Brake Band solenoid share a common +12 Vdc reference. To energize these solenoids the PCM grounds the control signal. The shift solenoids are On or Off, the Brake Band solenoid uses a 32 Hz Pulse Width Modulated (PWM) control signal.

In Drive 1st gear the Shift A solenoid is de-energized. When the Shift A solenoid is de-energized the fluid port is closed causing the A shift valve to be in the 1st and 4th gear position.

In Drive 1st gear the Shift B solenoid is energized. When the Shift B solenoid is energized the fluid port is also closed causing the B shift valve to be in the 1st and 2nd gear position.

If the Shift B solenoid is inoperative the open fluid port will cause the B shift valve to be in the 3rd and 4th gear position. Since the A shift valve is in the 1st and 4th gear position. The transmission will be in 4th gear as opposed to 1st gear. An inoperative Shift B solenoid also prevents 2nd gear from being selected.

L (Manual 1st gear) will produce the 1st gear ratio with an inoperative Shift B solenoid because L (Manual 1st gear) does not use the shift solenoids.

Your symptom suggests the Shift B solenoid is inoperative.
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Re: 99 Isuzu Trooper suddenly not changing gears! No DTC cod

Postby Bahram » Mon Jun 07, 2021 12:40 pm

Thank you Buster28 for your reply.
I will go ahead and replace solenoid B as per your suggestion A.S.A.P.
While I was waiting for a reply, I have done the following as well.
I have looked at the signals from the PCM output and confirmed a correct signal output for 1st, 2nd, 3rd, and 4th gear from PCM towards tranny.

Gear Solenoid A Solenoid B
-----------------------------------------
1 OFF ON (also P, R, and N positions)
2 ON ON
3 ON OFF
4 OFF OFF

I have also noticed a pulse getting supplied to Break Band Solenoid when shifting from N to D for 1 sec. (assuming that is how Break Band suppose to work) and signal stays Hi for all other shift positions.
I have also disconnected the PCM connectors and checked the resistance of solenoid to GND and for solenoid A and it was 20 Ohms and for B it was 22 Ohms and for Break Band Solenoid was 12 Ohms, and TCC also 22 Ohms.
I think I go with your suggestion and change the solenoid B. Perhaps I should change both A and B since they are the same age and I do not want to have another failure of solenoid A.
I will send an update after the repair.
Best regards,

Bahram
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Re: 99 Isuzu Trooper suddenly not changing gears! No DTC cod

Postby Khrizz07 » Mon Jun 14, 2021 8:07 pm

I was about to post a similar thread but found this one.

Were the solenoids the problem?

Here's my scenario: I took the car to the shop who actually re-built the transmission like 4 years ago for service (filter and fluid change). When taking the car for a spin, noticed the same, car won't go on Drive, felt like I was stepping on the brake pedal at the same time, the guy there said they noticed a broken connector down below with some loose wires as well and they cut them off saying it will cause a missfire or something.

Now the shop guy is saying the main harness going from the tranmission to the PCM is faulty and he needs a complete one to repair the issue?
Is this something that can happen?

He said he tried with some loose connectors but it wouldn't work since the wires are too burned and he can't get the correct colors and now he claims he needs the full harness. Do you think this would fix the issue (getting the whole harness)?

Car is on its 4 week at the shop.

Thanks.
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Re: 99 Isuzu Trooper suddenly not changing gears! No DTC cod

Postby Buster28 » Tue Jun 15, 2021 2:25 pm

Khrizz07 wrote:I was about to post a similar thread but found this one.

Were the solenoids the problem?

Here's my scenario: I took the car to the shop who actually re-built the transmission like 4 years ago for service (filter and fluid change). When taking the car for a spin, noticed the same, car won't go on Drive, felt like I was stepping on the brake pedal at the same time, the guy there said they noticed a broken connector down below with some loose wires as well and they cut them off saying it will cause a missfire or something.

Now the shop guy is saying the main harness going from the tranmission to the PCM is faulty and he needs a complete one to repair the issue?
Is this something that can happen?

He said he tried with some loose connectors but it wouldn't work since the wires are too burned and he can't get the correct colors and now he claims he needs the full harness. Do you think this would fix the issue (getting the whole harness)?

Car is on its 4 week at the shop.

Thanks.

This is the 4L30e transmission wiring schematic for your truck, repairing or replacing some or all nine wires is not difficult.
Click on schematic to expand.
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Re: 99 Isuzu Trooper suddenly not changing gears! No DTC cod

Postby Khrizz07 » Tue Jun 15, 2021 2:53 pm

Buster28 wrote:
Khrizz07 wrote:I was about to post a similar thread but found this one.

Were the solenoids the problem?

Here's my scenario: I took the car to the shop who actually re-built the transmission like 4 years ago for service (filter and fluid change). When taking the car for a spin, noticed the same, car won't go on Drive, felt like I was stepping on the brake pedal at the same time, the guy there said they noticed a broken connector down below with some loose wires as well and they cut them off saying it will cause a missfire or something.

Now the shop guy is saying the main harness going from the tranmission to the PCM is faulty and he needs a complete one to repair the issue?
Is this something that can happen?

He said he tried with some loose connectors but it wouldn't work since the wires are too burned and he can't get the correct colors and now he claims he needs the full harness. Do you think this would fix the issue (getting the whole harness)?

Car is on its 4 week at the shop.

Thanks.

This is the 4L30e transmission wiring schematic for your truck, repairing or replacing some or all nine wires is not difficult.
Click on schematic to expand.


Thank you. I will forward this to the mechanic, but the thing is what do they need to replace? Just wiring?
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Re: 99 Isuzu Trooper suddenly not changing gears! No DTC cod

Postby Buster28 » Tue Jun 15, 2021 3:26 pm

I don't know what else could be wrong with the transmission, but I do know the transmission won't operate correctly if any of the nine wires in the transmission wiring harness are shorted to ground or each other or open circuit.
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Re: 99 Isuzu Trooper suddenly not changing gears! No DTC cod

Postby Khrizz07 » Tue Jun 15, 2021 3:31 pm

Buster28 wrote:I don't know what else could be wrong with the transmission, but I do know the transmission won't operate correctly if any of the nine wires in the transmission wiring harness are shorted to ground or each other or open circuit.


Thanks again. Hopefully with the diagram he can have a better vision.
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Re: 99 Isuzu Trooper suddenly not changing gears! No DTC cod

Postby Bahram » Wed Jun 16, 2021 2:21 am

Khrizz07,
Based on what I have learned from our transmission guru Buster28 in this forum, I have decided to take the Trooper to a very trustworthy transmission shop for the repair. I explained what I have done and what I want him to replace (both solenoid A and B and perhaps their internal short harness). BUT I ask him to do his own troubleshooting since he has a transmission repair shop and I do not (I value his dedication to his trade anddo not want him to get an impression that I know more than him about the transmission :-S ).
I thought paying $400~$500 for two solenoids and replacing the oil and filter is a fair price. It is not easy when you do not have the place to work on a car at home.
This is what the mechanic came up with so far(he has my car for two days already):
He has eliminated the computer signals and wired the transmission externally to see if there is any computer or electrical wiring issues outside of the transmission. He noticed the transmission still does not go to the 2nd gear or the 3rd gear and he is now sure the problem is inside the transmission! (I appreciate his meticulous troubleshooting techniques but I also think this is not his first 4L30-E transmission either!!.;-)).
Perhaps he is trying to make the job worth the trouble since he can not trick me easily. I am hoping to have the car back tomorrow but I am still not sure. Will keep you posted.
I think I am going to pay over his initial estimate for his troubleshooting and ..... but I really did not like to get inside this transmission.

Regards,

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Re: 99 Isuzu Trooper suddenly not changing gears! No DTC cod

Postby Khrizz07 » Wed Jun 16, 2021 11:14 am

Hey Bahram, hopefully the transmission guy have good news for you. Found a trooper in a yard in "good condition" or at least in pictures. Today I will know if they have the complete harness from the PCM to the transfer case since according to the mechanic that's the issue.
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Re: 99 Isuzu Trooper suddenly not changing gears! No DTC cod

Postby Bahram » Fri Jun 18, 2021 10:34 pm

Hello everyone,
I got a phone call after 3 days from my transmission shop. He said that car is running fine. I went and paid for an oil/filter and seal which were expected. I also paid for three solenoids (I am guessing A, B, and a third one!!). I drove the car home. All good and dandy. My son drove it to his school this morning and called me in the afternoon from the side of a highway!
He said he has Check engine AMBER light and Check Transmission RED light on in his dashboard. I asked him to let it cool down before driving it again. My son claims the car was driving ~ 100 km/hr on a 2500 rpm. It seems to me that either transmission was slipping or it was not going to the forth gear. I got my code reader and see two P1870 error codes only!
I called the mechanic and he claims the car was running in the city for over 30 minutes trouble free. He wants to see the car again on Monday. I have told him before that I have added a secondary transmission radiator in series with the car radiator and I was wondering if there is a good oil flow through them. I guess he missed that.
My son and I gradually losing our trust in this car. I do not want my son to drive this car far distances anymore.
I have paid ~$900 and still have a questionable transmission.
Monday afternoon I may have more information to share.......
Anyone suggestions what to look for now?
Regards,
Bahram
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Re: 99 Isuzu Trooper suddenly not changing gears! No DTC cod

Postby Bahram » Fri Jun 18, 2021 10:50 pm

Hi Khrizz07;
I have posted a long reply below to update about what happened to me today.
I am assuming the harness will solve your transmission issue.
Last year I came across a 2000 Trooper with a good engine and transmission but only for parts. I bought the car since it was in an accident and was not worth the repair.
I thought I could use its engine and transmission to repair my 99 Trooper. What a mistake!!... I learned later that year 2000 engine and tranny are different from 99 and can not be interchanged!
Anyhow, keep me posted about your Trooper "challenge". :-)
Good luck,
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Re: 99 Isuzu Trooper suddenly not changing gears! No DTC cod

Postby Buster28 » Sat Jun 19, 2021 6:38 am

Bahram wrote:Hello everyone,
I got a phone call after 3 days from my transmission shop. He said that car is running fine. I went and paid for an oil/filter and seal which were expected. I also paid for three solenoids (I am guessing A, B, and a third one!!). I drove the car home. All good and dandy. My son drove it to his school this morning and called me in the afternoon from the side of a highway!
He said he has Check engine AMBER light and Check Transmission RED light on in his dashboard. I asked him to let it cool down before driving it again. My son claims the car was driving ~ 100 km/hr on a 2500 rpm. It seems to me that either transmission was slipping or it was not going to the forth gear. I got my code reader and see two P1870 error codes only!
I called the mechanic and he claims the car was running in the city for over 30 minutes trouble free. He wants to see the car again on Monday. I have told him before that I have added a secondary transmission radiator in series with the car radiator and I was wondering if there is a good oil flow through them. I guess he missed that.
My son and I gradually losing our trust in this car. I do not want my son to drive this car far distances anymore.
I have paid ~$900 and still have a questionable transmission.
Monday afternoon I may have more information to share.......
Anyone suggestions what to look for now?
Regards,
Bahram

DTC P1870 can indicate the Torque Converter Clutch (TCC) is slipping or not applied when it should be applied. It can also indicate a slipping transmission 4th ("Overdrive") clutch. 2500 rpm @ 100Km/h suggests a TCC problem, the expected rpm in 4th gear ("Overdrive") with the TCC locked up is about 2200 rpm.

What was the third solenoid that was replaced?
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Re: 99 Isuzu Trooper suddenly not changing gears! No DTC cod

Postby Bahram » Sat Jun 19, 2021 1:57 pm

Buster28 wrote:
Bahram wrote:Hello everyone,
I got a phone call after 3 days from my transmission shop. He said that car is running fine. I went and paid for an oil/filter and seal which were expected. I also paid for three solenoids (I am guessing A, B, and a third one!!). I drove the car home. All good and dandy. My son drove it to his school this morning and called me in the afternoon from the side of a highway!
He said he has Check engine AMBER light and Check Transmission RED light on in his dashboard. I asked him to let it cool down before driving it again. My son claims the car was driving ~ 100 km/hr on a 2500 rpm. It seems to me that either transmission was slipping or it was not going to the forth gear. I got my code reader and see two P1870 error codes only!
I called the mechanic and he claims the car was running in the city for over 30 minutes trouble free. He wants to see the car again on Monday. I have told him before that I have added a secondary transmission radiator in series with the car radiator and I was wondering if there is a good oil flow through them. I guess he missed that.
My son and I gradually losing our trust in this car. I do not want my son to drive this car far distances anymore.
I have paid ~$900 and still have a questionable transmission.
Monday afternoon I may have more information to share.......
Anyone suggestions what to look for now?
Regards,
Bahram

DTC P1870 can indicate the Torque Converter Clutch (TCC) is slipping or not applied when it should be applied. It can also indicate a slipping transmission 4th ("Overdrive") clutch. 2500 rpm @ 100Km/h suggests a TCC problem, the expected rpm in 4th gear ("Overdrive") with the TCC locked up is about 2200 rpm.

What was the third solenoid that was replaced?


Do not know. I will ask on Monday for sure.
I do not know much about the transmission issues but love to learn how it works and why do they fail. I just do want to drive to a remote location when I can not be sure I can drive back home trouble free.
Appreciate all the feedback I get from you.
I also placed an order for the LF wheel sensor to fix my ABS issue as you recommended.
I will try to trouble shoot the failed sensor when I get a chance. Most likely cable has been damaged due to constant vibration.
Regards,
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Re: 99 Isuzu Trooper suddenly not changing gears! No DTC cod

Postby Bahram » Wed Jun 23, 2021 5:19 pm

Bahram wrote:
Buster28 wrote:
Bahram wrote:Hello everyone,
I got a phone call after 3 days from my transmission shop. He said that car is running fine. I went and paid for an oil/filter and seal which were expected. I also paid for three solenoids (I am guessing A, B, and a third one!!). I drove the car home. All good and dandy. My son drove it to his school this morning and called me in the afternoon from the side of a highway!
He said he has Check engine AMBER light and Check Transmission RED light on in his dashboard. I asked him to let it cool down before driving it again. My son claims the car was driving ~ 100 km/hr on a 2500 rpm. It seems to me that either transmission was slipping or it was not going to the forth gear. I got my code reader and see two P1870 error codes only!
I called the mechanic and he claims the car was running in the city for over 30 minutes trouble free. He wants to see the car again on Monday. I have told him before that I have added a secondary transmission radiator in series with the car radiator and I was wondering if there is a good oil flow through them. I guess he missed that.
My son and I gradually losing our trust in this car. I do not want my son to drive this car far distances anymore.
I have paid ~$900 and still have a questionable transmission.
Monday afternoon I may have more information to share.......
Anyone suggestions what to look for now?
Regards,
Bahram

DTC P1870 can indicate the Torque Converter Clutch (TCC) is slipping or not applied when it should be applied. It can also indicate a slipping transmission 4th ("Overdrive") clutch. 2500 rpm @ 100Km/h suggests a TCC problem, the expected rpm in 4th gear ("Overdrive") with the TCC locked up is about 2200 rpm.

What was the third solenoid that was replaced?


Do not know. I will ask on Monday for sure.
I do not know much about the transmission issues but love to learn how it works and why do they fail. I just do want to drive to a remote location when I can not be sure I can drive back home trouble free.
Appreciate all the feedback I get from you.
I also placed an order for the LF wheel sensor to fix my ABS issue as you recommended.
I will try to trouble shoot the failed sensor when I get a chance. Most likely cable has been damaged due to constant vibration.
Regards,
Bahram




Hello everyone,
I have asked about the third solenoid.
Mechanic simply said: 1-2 solenoid,2-3 solenoid, and 3-4 solenoid!! Interesting!!! I did not know.....
I have some bad news. today is the third day I have the car in the transmission shop.
I just got an update that the problem is PERHAPS the TCC and oil link to it and it requires a transmission overhaul.
He quoted me anther $3K.
It means including the solenoid repair this transmission repair will cost $3900 !!
It is very disappointing to me since I just replaced the engine head gaskets and was looking forward to use the car trouble free for a while.
This may be the end for my Trooper experience.

I would like to thank you all for the tips and suggestions on this matter.

Regards,

Bahram
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Re: 99 Isuzu Trooper suddenly not changing gears! No DTC cod

Postby Buster28 » Thu Jun 24, 2021 10:19 am

Bahram wrote:Hello everyone,
I have asked about the third solenoid.
Mechanic simply said: 1-2 solenoid,2-3 solenoid, and 3-4 solenoid!! Interesting!!! I did not know.....

There is a 1-2&3-4 solenoid ("Shift A") and a 2-3 Solenoid ("Shift B"). Your shift problem involved the Shift B solenoid.
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Re: 99 Isuzu Trooper suddenly not changing gears! No DTC cod

Postby Bahram » Thu Jun 24, 2021 12:24 pm

Buster28 wrote:
Bahram wrote:Hello everyone,
I have asked about the third solenoid.
Mechanic simply said: 1-2 solenoid,2-3 solenoid, and 3-4 solenoid!! Interesting!!! I did not know.....

There is a 1-2&3-4 solenoid ("Shift A") and a 2-3 Solenoid ("Shift B"). Your shift problem involved the Shift B solenoid.



Yes Buster28,
Your diagnosis was correct. Mechanic has changed the solenoids and the transmission is changing gear flawlessly, but when I drive on a highway for 10 minutes it gives Check Transmission error DTC 1870. Apparently it is caused by TCC.
I am going to pick my car up this afternoon as is (not repaired) since I can not afford additional $3000 repair bill.
Thanks,

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Re: 99 Isuzu Trooper suddenly not changing gears! No DTC cod

Postby Buster28 » Thu Jun 24, 2021 7:37 pm

A Reman Torque Converter is less than 200 bucks.
It would be a good idea. imho, to check the resistance of the TCC solenoid coil at the PCM connector J2 (White) Pins D2 and C8 to ensure there are no open circuits that could prevent the TCC solenoid from operating. Note that DC current path is chassis ground, high resistance ground can prevent the solenoid from operating. The expected coil resistance is about 18 Ohms. An inoperative TCC solenoid can produce DTC P1870.
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