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Engine Trouble Code

2K views 13 replies 6 participants last post by  gorf1000 
#1 · (Edited)
First off I'm a newbie to posting here but a frequent reader, and a long-time mopar man.

I've had the oh-so wonderful intermittent limp-mode lockup problem with my '96 Intrepid (EDIT: 3.5L, 120k miles). I only bought the car about 2 weeks ago and it'll run fine for a day or so, or sometimes a block or two then it'll lock into limp mode. I can do the 5-times key dance to get the tranny to reset and then it'll run fine for a while again.

When I first got the car I checked the tranny fluid and it was about 2 quarts low so I probably have a leak, but as I've been watching it since then it hasn't dropped much so I'm not too concerned about that yet. After filling the tran fluid I'm still having the problem. Since my odometer was still working I thought perhaps the input speed sensor had been cooked so I swapped that out, worth the $20 chance. No help.

I had a loose ground as well, fixed that but still no luck.

I got my friend to run the codes on the computer (of course I now confirmed that whoever had the car before me removed the check engine light). We came up with the code "P1784". After looking through a ton of sites the best I've come up with for a description is:
*L-R Pressure switch circuit
---Possible causes - Low battery voltage

Now I did also notice on the scanner that the Throttle Position Sensor was not reading correctly (it was reading 17% at idle and went all over the place when hitting the gas).

Okay so with all that I would guess that the TPS needs to be replaced but can anyone give me an explanation as to what that code means and an idea of what may be a resolution? Thanks for all your help!
 
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#6 ·
Have you tried fixing the check engine light so that you can pull up the two digit codes from the key dance method? I know that the code you got is more acurate but without a factory service manual I don't know where to find info on P1784. Like you said you already tried scouring the web for it.

You also said that the throttle position sensor was giving bad readings. This could be your problem if A) that has a bad connection or B) the sensor itself is bad. According to the wiring diagrams for the transmission control module (TCM) the TCM does use the signal from the throttle sensor. If some days the throttle sensor is acting better than others then maybe it's on the other days that the tranny goes into like mode? I just went through an episode with my car where the coil pack wiring ended up being messed up. While the tranny never went into limp mode it did shift bad at times and there was even a code logged that indicated that the TCM had logged codes.
 
#7 ·
I agree with ITrep96. If your TPS is jumping all over who knows what the trans. might think is going on.

I had that code on my 94 also, but mine turned out to be a bad TCM. Bad solider joint on the board.
 
#8 ·
I wanted to post an update since it always drives me nuts when someone has a problem and never replies with a solution.

Well I took my car to one dealership here in NJ (which I won't mention here but if you want to know who they are to stay away PM me). They told me that there were signs of converter failure and that the valve body would need to be replaced along with a laundry list of other items including trans lines leaking, oil sending unit leaking, suspension issues, and others. They recommended a tranny replace rather than a rebuild due to the car having 117k on it, they quoted me $3200 :wow: So I took it to another dealer where my bro-in-law has had his cars worked on for over a decade. They looked it over decided it needed a new solenoid pack and motor mount and, tie-rod bushings and sway bar links. They quoted me $530 for the tranny/mount (including a fluid flush since they dropped the valve body), and $500 for the suspension stuff (including an alignment), so for less than a third of the cost I have a very nicely running Intrepid (minus the shot brakes I need to replace ;) )

So I'm very happy I didn't take a first estimate or I would've been taken for a serious ride.

I do however have a new issue though it's not inhibiting yet. I had a Code 24 (TPS voltage high/low) before it went in and when I metered the TPS it was reading 1V at close and 5V at full open so I would say it was running high (stupid auto stores don't carry the right TPS and the dealer wants an arm and a leg for it). However today my light went back on and when I checked it it still had the 24 but it also had a code 25 ("Automatic Idle Speed (AIS) motor driver circuit shorted or target idle not reached, vacuum leak found"). Could this be a result of the TPS not reading correctly since it says idle not reached, or is it more likely they missed a vaccuum line when working on my car?
 
#9 ·
Don't know what to tell you about your TPS.

I would however think twice about flushing the trans. If you current fluid is not burnt or discolored I would not do a flush just a fluid/filter replace. Seems a lot of people that have flushes end up having more problems than before.
 
#10 ·
534 dollars to replace the transmission mount and a flush are u sure u got a good deal there. The transmission mount only costs like 50 bucks and takes 15 minutes to replace a flush shouldn't cost more than 120 bucks. For the rest I would replace the TPS and the IAC, also do you have the limp mode issue any more?
 
#13 ·
Not positive on our mopars, but on gm the tps high is set if the pcm thinks the tps voltage is staying higher than it should be for the running engine parameters. It is suppose to indicate a possible bad tps. If you haven't replace the tps yet I would. Find a auto part store that has one. Find one on ebay even. Have any u-pullits around could find one there.
 
#14 ·
I'm willing to bet that while they were doing the work at the shop that they either forgot to reconnect a vac. line or knocked one loose. As for the TPS code I did meter the TPS and it was reading 1V at close and 5V at full open which is high so it probably needs to be replaced. I have to make time at some point to go to a junkyard to get a new TPS or break down and spend the $80 at a dealer to get one since all the autoparts stores carry a TPS which isn't the right connector for this engine.
 
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