TROUBLE CODE IS P0734 - A/T Won't Shift Into Last Gear

JAKECRAWFORD2

MEMBER
1998 SATURN SL2
149,000 MILES

In a nutshell. 1998 Saturn SL2 Auto Tranny does not shift into overdrive (last gear). No other problems with tranny at all. Shifts perfect except for when its time to shift into the last gear going about 40-50 mph. It tries to go into OD once and the RPM's rev then it goes back into fourth and stays. TROUBLE CODE IS P0734 - Incorrect 4th Gear Ratio (this is the only code that it ever gave for me and the previous owner - no other issues with tranny). I checked all electrical connections, cleaned with electric cleaner spray, put ohm meter to wire harness on valve body and solenoids checked OK at right resistance. Board that snaps over the solenoids in valve body looks in good shape too. Fluid and filter are new and at proper level. I bought a new shift solenoid but have not put it in yet because they all read proper resistance and I am unsure if this is the cause. MY QUESTION IS. Can a solenoid still be bad or partially failed even though it shows proper resistance? Can the A/T fluid temperature sensor cause the overdrive to slip and not engage? What other parts can cause this? (Clutch pack for that gear? Transaxle range switch out of adjustment?) I want to get some advice from professionals before I take the valve body apart again. Thanks in advance and any help would be greatly appreciated!

5 Replies

SATURNTECH9

MECHANIC
30,869 POSTS

Heres my take on this one iam a factory trained saturn tech and knows these transmission really well. Is there a delay in reverse at all?If so how many seconds?You most likely have one of two things going on here Low transmisson line pressure which effects the gears more so then the lower ones. Or the 4TH gear clutch piston is leaking pressure. If you have a injector tester that can pluse the injectors you can use that to test the 4th gear actuator itself. But to test the pcm wires and actuator itself you will need a pdt or tech 2 scan tool with the saturn software. To check the 4TH gear clutch piston you would have to remove the valve body and set your air compressor outtlet regulator to 60psi. Then get a rubber tipped blow gun thay wasnt osha approved and restricted for outtlet pressure. Then use that to air check the 4TH gear clutch piston to see if it holds pressure and doesnt leak.I would also check the 1st 2nd 3rd and reverse servo piston by air checking them while your in there.I would start by doing a high low line pressure test on the transmission before air checking the clutches.I would also recomend doing a step pressure test also where you watch to see if the computers commanded pressure at different pressures from low to high matches. But again that requires a pdt or tech 2 scan tool with the saturn software. To do the high low line pressure test it requires a transmission gauge pressure tester.I recomend one to you its the one I have is pretty cheap but really nice. Also the transmission temp sensor isnt going to cause the 4th gear code or lack of engagement.

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Thursday, January 12th, 2012 AT 4:47 PM

JAKECRAWFORD2

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3 POSTS

No delay in reverse. It look like the only thing I am able to do myself is check the 4TH gear clutch piston. Where do I apply the air? Is it that hole over the 4TH gear solenoid? Also, could this be causes by incorrect pattern select switch location? Is it better for me to just buy a a rebuilt valve body over taking it to a saturn shop? At $139 for the part, it might cost the same in labor at a shop. Thanks

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Thursday, January 12th, 2012 AT 4:59 PM

SATURNTECH9

MECHANIC
30,869 POSTS

To air check the cutches you have to remove the valve body completely and blow air into the 4Th gear port on the transmission case. You can do a high low test yourself thats where you can the line pressure at idle with the trs LP fuse in then check the pressure with the fuse out. You just need to get a transmission pressure gauge test kit. The one I have was like 70 or under and is made by otc its really nice does oil pressure also. Its not a selector switch issue that would set a different code. Where is this rebuilt valve body for 139?Send me the link to check it out.I can tell you this I tried buying some rebuilt valve bodies that were pretty cheap turn out to be a nightmare. So I got the tools and now I rebuild my own valve bodies. They really arent rebuilt they still have the actuators etc they just ohms check them etc.

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Thursday, January 12th, 2012 AT 5:32 PM

JAKECRAWFORD2

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3 POSTS

I just reopened the valve body and switched around the shift solenoids and it did not change anything. Here is the site for the valve body @ 139. http://800700tran.com/prod.itml/icOid/270

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Thursday, January 12th, 2012 AT 7:20 PM

SATURNTECH9

MECHANIC
30,869 POSTS

It doesnt sound like that valve body has any sonnax upgrades I highly recomend getting one with the sonnax upgrades.I rebuilt my 1999 saturn SL 2 valve body with the full blown sonnax upgrades with the sure cure kit. It includes the pressure regulator sleeve pressure regulator pressure regulator spring and the boost valve. We need to do a high low pressure test on the transmission before doing any air checks. Do want me to recomend a transmission pressure test kit?I have a otc set and its really nice and not real expensive.