Transmission oil pressure sensor broke - code P703

4433 Views 11 Replies 4 Participants Last post by TransEngineer, Feb 7, 2016

jclifford3rd

Discussion Starter · Jan 11, 2016

2006 Dodge Ram 2500 Power wagon with 57,000 miles on it – I was off road hunting, when I got back to hard road the check engine light came on, It drove fine through 1st ,2nd, 3rd gear, when it hit drive it totally slipped, I pulled over and looked under it, no leaks or anything obviously wrong, started again, same fine up to drive and it slips as it goes into drive. I drove it 2 miles home in 3rd gear without any slipping. Once in my garage my error code reader gave me a P703 error, Google pointed me to the transmission sensor and I discovered the “Transmission oil Pressure sensor” had broken in half. Guessing a stick or rock caught the wire. So I removed both halves of it and went to Autozone to buy a new one. After installing the new one the truck would go forward and backward in my garage without problem but the check engine light was still on, so before trying to drive it I used my code reader to clear the error code. Now the truck will not move in any gear, Nothing at all, dropping in gear does not put load on engine or seem to engage the transmission at all. I checked the fluid not running vs. running and it does drop about 1/8 of an inch. I reset the ECM by pulling the correct fuse and turning on the key until it beeps 2 times, replacing the fuse and hoping a reset of the ECM would clear the issue. Nothing. I unhooked the battery cable overnight again hoping to reset the error condition, no help. Why would resetting the error code change the transmission problem? Is something else still need to be cleared? Hard for me to believe the transmission clutches are ruined when reverse / 1st worked one minute but not right after clearing the code. I understand the limp home mode should have been allowed me to drive it at a low speed. I understand drop in fluid pressure is why bands fail, but this doesn’t make sense. I have no error codes at this time.

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TransEngineer

· #6 · Jan 14, 2016

Could you double-check the fault code? Should have 5 digits (typically "P" plus 4 numbers), such as P0734. P703 is not a valid code.

The broken line pressure sensor would not cause a trans failure. The PCM would recognize that it was getting a bad signal, and would switch to "open loop" line pressure control.

Will your reader display any info other than fault codes? Like maybe (hopefully) turbine (trans input) speed, output speed, line pressure, and desired line pressure?

Have you confirmed that the transfer case is not in Neutral? Can you have someone watch underneath the truck (when you put it in gear) to see if either driveshaft is spinning?

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TransEngineer

· #8 · Jan 15, 2016

jclifford3rd said:
It was a PO730, gear ratio incorrect displayed on the code reader, now that it has been cleared I have no codes. I did try moving transfer case from 2x to 4x and it works the same, I will get some to shift while I am looking from under it looking for any shaft movement. Thank you

Hmmm... P0730 is not a valid fault code for a 545RFE trans (which is what you should have). So that's kinda strange.

See if you can buy (or borrow) a scan tool that will display the speeds and line pressure readings. That's really the next step in diagnosing it. Or have a dealer or shop (with a scan tool) read them for you (which is obviously difficult if the truck won't move). I would check:
• Does the line pressure reading match the Desired Line Pressure, idling in Park? If it reads 30 psi, shut it down, you likely have no line pressure (the sensor reading should not go below 30 psi, so a 30 psi reading means 30 psi OR LESS).
• If line pressure is low (and assuming fluid level is OK), then drop the pan and check the filters. Look for filter that is loose, fallen off, cracked, or split open. Also check that snout of the main (flat) filter is pushed up THROUGH the seal in the pump housing. If filters are OK, then you probably have a stuck regulator valve (inside the pump assy), which means pull the trans out, pull the pump out, split it apart, and inspect / clean the valves. If you're gonna do this yourself, check back with me first for some VERY important tips.
• If line pressure is OK (matches Desired LP within a few psi), then check turbine (input) and output speeds. In Park with engine running, output will be zero, input should be roughly equal to engine speed. Shift into Drive (or Reverse). You should see turbine speed drop to zero as trans engages. See what happens. No change in turbine speed? Output speed comes up to some positive value? If turbine does not drop to zero, then shift back to Park. Don't sit there for more than a few seconds (in gear, with turbine above zero) or you will smoke one (or more) of your clutches.

So see if you can get your hands on a scan tool, and try these checks. They will help to pinpoint where the real problem is.

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TransEngineer

· #12 · Feb 7, 2016

OK, Park still holds the truck OK? And it will roll in Neutral?
Does the dash display look correct (P, R, N, D) as you shift through the gear positions?

I would shift the transfer case into Neutral (trans in Park) and have someone push or tow you to a shop that has a scan tool to monitor the line pressure and the speeds (engine, turbine, and output speeds). I suspect you have complete loss of line pressure, but it would be best to check with a scan tool to confirm this (before you pull the trans oil pan and/or pull the transmission!).

If you absolutely can't borrow a scan tool, or get it to a shop, then I would drop the trans oil pan and check both filters. Make sure the spin-on filter is snug (not loose, not lying in the pan), and that the main (flat) filter is properly installed (its plastic snout should be pushed up THROUGH the seal in the pump housing, not just resting against it), and is not split open along the side seam, or cracked at the base of the plastic snout.

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