Transmission Woes Continue!

[BillHill93]

P0758 code. I've tested both the a and b solenoid for resistance and get around 23 ohms. I've also tested the 3-2 downshift solenoid, the EPC, and the PWM solenoid. They all check out good. I've checked the harness for continuity all the way from the PCM plug to the solenoids. I've also checked the harness for an external ground. The harness is good. What in the world should I do next to try to figure why I keep getting this code? Transmission will act fine one day and then the next I'll be going down the road and the RPMs will rev up and it slams into gear. Then it will lose 1st and 4th gear all together but then the next time I drive it it's fine. I would think that if the PCM was bad this problem would be more constant. I've read throttle position sensor and vehicle speed sensor but I hate to just throw parts at it. What next? The valve body?

 

[BillHill93]

One other thing also sometimes lose the second gear and just stays in third all the way from a dead stop to as fast as you want to take it.

 

[Jimmyy]

I'm no expert on transmission, but in ohm-ing out the solenoids. All you are doing is making sure the coil is ok. The mechanical function could still be bad.

 

[rockola1971]

Whats your fluid look like? Smell burnt? Have you dropped the pan and taken a look? Checked PCM wiring harness connections for the green crusties?

 

[Joseph Garcia]

@NickTransmissions may be able to provide some perspective on your issues, as he is our resident transmission expert.

 

[BillHill93]

I'm no expert on transmission, but in ohm-ing out the solenoids. All you are doing is making sure the coil is ok. The mechanical function could still be bad.

I suspected that the B solenoid could still be faulty so I did replace it but the problem still persists and I am still getting the same p0758 code intermittently.

 

[BillHill93]

Whats your fluid look like? Smell burnt? Have you dropped the pan and taken a look? Checked PCM wiring harness connections for the green crusties?

I did drop the pan and change the fluid and filter when I first replaced the B solenoid. The fluid was clean. There was no noticeable corrosion on the PCM harness when I checked.

 

[Trackman]

P0758 code. I've tested both the a and b solenoid for resistance and get around 23 ohms. I've also tested the 3-2 downshift solenoid, the EPC, and the PWM solenoid. They all check out good. I've checked the harness for continuity all the way from the PCM plug to the solenoids. I've also checked the harness for an external ground. The harness is good. What in the world should I do next to try to figure why I keep getting this code? Transmission will act fine one day and then the next I'll be going down the road and the RPMs will rev up and it slams into gear. Then it will lose 1st and 4th gear all together but then the next time I drive it it's fine. I would think that if the PCM was bad this problem would be more constant. I've read throttle position sensor and vehicle speed sensor but I hate to just throw parts at it. What next? The valve body?

I replaced my transmission at 248,000. I was out of town - it began to get noisy and wouldn't shift up. Teltale was the smell and appearance of the fluid

 

[rockola1971]

Are you sure it isnt losing 2nd and 4th instead of 1st and 4th? Was tranny pan full of black dust?

 

[BillHill93]

When the issue occurs it loses first, second, and fourth. It will stay in third gear from a complete stop to as fast as I want to take it and never shift. Then the very next day it may very well run all day long without a single issue. When I pulled the pan the tranny fluid was clean and red. The tranny pan was clean also. What would black dust in the tranny pan indicate?

 

[rockola1971]

When the issue occurs it loses first, second, and fourth. It will stay in third gear from a complete stop to as fast as I want to take it and never shift. Then the very next day it may very well run all day long without a single issue. When I pulled the pan the tranny fluid was clean and red. The tranny pan was clean also. What would black dust in the tranny pan indicate?

Black dust would be either material from the 2-4 band and/or clutch material. Some is completely normal on an older tranny but and excessive amount would indicate a burnt up 2-4 band and/or burnt clutches but that would usually make the fluid an orange to brownish color and have a very distinct burnt smell. Assuming you arent having electrical problems caused by corrosion at plug connections I would have to say you have a well worn valve body and valves are sticking in their bores. May also have check balls peening your separator plate which comes with tranny old age.

 

[NickTransmissions]

When the issue occurs it loses first, second, and fourth. It will stay in third gear from a complete stop to as fast as I want to take it and never shift. Then the very next day it may very well run all day long without a single issue. When I pulled the pan the tranny fluid was clean and red. The tranny pan was clean also. What would black dust in the tranny pan indicate?

Like @rockola1971 said, black dust is a bad sign, if in quantity at the bottom of the pan. You're also going in and out of limp mode (3rd and reverse only).

Did you continuity-test all the solenoids when the pan was off? Visual inspections are fine but only tell half the story...

You need to find the source of the electrical fault that's putting the transmission into limp mode first. Once it's free of electrical problems, only then will you be able to appraise its mechanical health.

My gut tells me it's coming out sooner rather than later but could be wrong...

 

[BillHill93]

Like @rockola1971 said, black dust is a bad sign, if in quantity at the bottom of the pan. You're also going in and out of limp mode (3rd and reverse only).

Did you continuity-test all the solenoids when the pan was off? Visual inspections are fine but only tell half the story...

You need to find the source of the electrical fault that's putting the transmission into limp mode first. Once it's free of electrical problems, only then will you be able to appraise its mechanical health.

My gut tells me it's coming out sooner rather than later but could be wrong...

I bought a new female plug for the pass-through connector. I installed that new female plug and with it I tested both the a and b solenoid, the 3-2 downshift solenoid, the electronic pressure control solenoid, and the pulse width modulation solenoid for the proper ohms. They all gave the correct readings and by doing it this way it also led me to believe that the internal harness was good. I then tested the a and b solenoid for ohms all the way from the green connector on the PCM. Again I got the correct readings. Doing this also lead me to believe that the wires from the PCM connector to the a and b solenoid were good. I also tested for an external ground and there was none. I continue to get a p0758 code. If there is an electrical issue then I'm not sure where to check next.

 

[NickTransmissions]

I bought a new female plug for the pass-through connector. I installed that new female plug and with it I tested both the a and b solenoid, the 3-2 downshift solenoid, the electronic pressure control solenoid, and the pulse width modulation solenoid for the proper ohms. They all gave the correct readings and by doing it this way it also led me to believe that the internal harness was good. I then tested the a and b solenoid for ohms all the way from the green connector on the PCM. Again I got the correct readings. Doing this also lead me to believe that the wires from the PCM connector to the a and b solenoid were good. I also tested for an external ground and there was none. I continue to get a p0758 code. If there is an electrical issue then I'm not sure where to check next.

I wonder if Shift Sol B has failed mechanically but the windings inside of it are still putting out the correct resistance...Just a guess....You can swap the two shift solenoids to see if the code changes...If it does and you get a DTC for Sol A, like P0753 (which would be the same solenoid that is now in the 'B' location), you found the problem...If you're still getting Sol B code, drop the valve body and check the 2-3 shift valve, 2-3 shuttle valve (both are behind Solenoid B) and the 3-2 downshift valve to see if any are stuck or dragging...There's no spring tension behind the 2-3 shift and shuttle valve as there's no spring in that bore...Just the two valves: Shuttle valve is outboard, shift valve is inboard.

 

[BillHill93]

I wonder if Shift Sol B has failed mechanically but the windings inside of it are still putting out the correct resistance...Just a guess....You can swap the two shift solenoids to see if the code changes...If it does and you get a DTC for Sol A, like P0753 (which would be the same solenoid that is now in the 'B' location), you found the problem...If you're still getting Sol B code, drop the valve body and check the 2-3 shift valve, 2-3 shuttle valve (both are behind Solenoid B) and the 3-2 downshift valve to see if any are stuck or dragging...There's no spring tension behind the 2-3 shift and shuttle valve as there's no spring in that bore...Just the two valves: Shuttle valve is outboard, shift valve is inboard.

If in fact one of the valves are stuck does that mean that the valve body would need to be replaced? Also I would assume that since this issue is so random that it would mean that the valve is not sticking all the time. Is that a correct assumption? Sometimes I can drive a hundred miles without a single issue. Shifts through every year just fine. Other times it starts having shifting issues within the first 5 miles of driving. That's why it's so puzzling to me.

 

[rockola1971]

If in fact one of the valves are stuck does that mean that the valve body would need to be replaced? Also I would assume that since this issue is so random that it would mean that the valve is not sticking all the time. Is that a correct assumption? Sometimes I can drive a hundred miles without a single issue. Shifts through every year just fine. Other times it starts having shifting issues within the first 5 miles of driving. That's why it's so puzzling to me.

The symptoms mirror either a mechanical/electrical problem with shift solenoid(s) and/or worn valve body. A solenoid can check good cold but become a demon when it gets warmed up but your description of frequency of going into limp mode just doesnt fit that. This wreaks more of a highly worn valve body. I would get yours serviced and rebuilt or order a replacement new/rebuilt valve body.

 

[BillHill93]

The symptoms mirror either a mechanical/electrical problem with shift solenoid(s) and/or worn valve body. A solenoid can check good cold but become a demon when it gets warmed up but your description of frequency of going into limp mode just doesnt fit that. This wreaks more of a highly worn valve body. I would get yours serviced and rebuilt or order a replacement new/rebuilt valve body.

Thank you sir. You have definitely given me a more definitive direction to look deeper into.

 

[NickTransmissions]

Thank you sir. You have definitely given me a more definitive direction to look deeper into.

If you haven't already purchased a reman valve body, you can vacuum test yours (or take to it to a transmission shop that has a Sonnax vac test machine) and they can test it, if you want to definitively rule in or out the valve body.