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Transmission switches to lower gear on it's own!
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joezapp
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Jun 6, 2015, 9:38 AM
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Transmission switches to lower gear on it's own!
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Hi. Here is a problem that began in mid-April. On that day, the tranny "clunked" while on a highway, and then performed as if it were in 2nd gear. The car speed would max out at 35-40 mph. I then changed the tranny filter and gasket and added the appropriate fluid. Since then, and it's now early June, it is still consistent that the car performs normally on start-up as if nothing is wrong. About 1/2 hour into the drive, upon braking, I will get the "clunk". That is my warning that the car will now operate in 2nd gear and won't go over 35-40mph. When I turn the car off, wait a bit, and start it back up, it will be fine until I get the "clunk" again. I can only assume that when the tranny or engine reaches a high temperature, the tranny is shifting by itself to 2nd gear. I have no idea why. The car is a 1999 Dodge Stratus 2.4 with 80,000 miles.
Can anyone tell me why this is occurring? I'm limited to only driving this car locally at this point. Thanks so much!
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gsferraro
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Jun 6, 2015, 12:35 PM
Post #2 of 38
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Re: Transmission switches to lower gear on it's own!
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Hello,
Im Gary, i have a trans shop in new york. What is happening to your car is, it going into whats called failsafe mode. Failsafe on this car is 2nd gear only. When you turn the car off, your actually erasing the memory of the transmission control module(its forgetting it has a problem). What failsafe is, is when the trans module turns off all solenoids, theres no electric flowing through the solenoids. What to do next is get the trans module scanned to get the codes. If a transmission shop has a free check ask them to scan the car and tell you what codes are present and ask them to write down the c.v.i(clutch volume index)values. One thing you can do if you have the l.e.d read out on your dash, turn your key to position 2, 3 times and on the 3rd time leave it in position 3 and look at where the speedo reads and it should flash codes(some do and some dont).
The bottom line is, your car is going into failsafe because the trans module sees something it doesnt like, so we need the codes that are present to see what direction to go. c.v.i values would be key as well. What ever that clunk is the trans module doesnt like what it seeing. Gary
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joezapp
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Jun 6, 2015, 9:14 PM
Post #3 of 38
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Re: Transmission switches to lower gear on it's own!
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Hi Gary. I'm glad that I also found you here, because that other location has errors with posting and replying.
I never knew about a fail-safe mode! And you are absolutely correct in that the Check Engine light came on. I should have mentioned that, but you already knew that it had to be on. I DO have a code reader. I'll report back tomorrow with what it reads. That will be a start. Thanks so much!
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gsferraro
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Jun 7, 2015, 4:07 AM
Post #4 of 38
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Re: Transmission switches to lower gear on it's own!
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Ok, sounds good. Gary
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joezapp
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Jun 7, 2015, 10:25 PM
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Re: Transmission switches to lower gear on it's own!
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Hi Gary. As you probably guessed, I have P0700 as an OBD code. I realize this tells us little. I have to see what the TCM code reads, and try to get that other info you need as well. I will check with my mechanic to see if he has the code reader at his shop, or if he has a connection with someone who can scan it for me. I can also check with my auto parts store for a connection. I know that you're in NY. I don't know what part of NY, but I used to live in Staten Island. I'm now in Central Jersey just outside Staten Island. Any chance you have a connection with someone in New Jersey who would do a free scan?
Joe
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gsferraro
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Jun 8, 2015, 2:45 AM
Post #6 of 38
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Re: Transmission switches to lower gear on it's own!
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Hello,
I attended a seminar in march and had lunch with the guy that owns cedar grove transmissions, is that near you? Also, have you tried autozone? If anything call around your area to your local transmission shop and see if they have a free diagnostic scan. The p0700 is on the engine side so we would need to get into the tcm and get the codes. Gary
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joezapp
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Jun 8, 2015, 6:23 AM
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Re: Transmission switches to lower gear on it's own!
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Hi Gary. Yes, I plan to give Autozone a shot after talking to my mechanic. Cedar Grove Transmissions is also an option, so thanks for that. I'll report back once I have the info. You've been a great help already!
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gsferraro
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Jun 8, 2015, 6:55 AM
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Re: Transmission switches to lower gear on it's own!
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No problem, glad i can help. I will wait to hear from you with the codes. Gary
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joezapp
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Jun 9, 2015, 2:29 PM
Post #9 of 38
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Re: Transmission switches to lower gear on it's own!
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Hi Gary. My mechanic's scan tool was able to narrow this down further. He pulled P0725 Engine Speed Sensor Input Circuit Malfunction. Seems that this code means that it could be the input sensor, or the crank sensor, or the TCM, or corroded connections/wiring. I'm glad that the problem isn't internal. I suppose I will need to narrow this down further by getting the TCM codes and the c.v.i. from a trans shop as you suggested, correct? Also, for the record, the speedometer is working fine, so we can rule out the VSS. Thanks so much...
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gsferraro
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Jun 10, 2015, 4:55 AM
Post #10 of 38
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Re: Transmission switches to lower gear on it's own!
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Hello,
The 725 code is the crank position sensor, The sensor is located in the bellhousing of the trans, becareful if your going to change it, make sure its adjusted correctly. Thats the direction i would go first, take care of that first. gary
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joezapp
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Jun 10, 2015, 2:30 PM
Post #11 of 38
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Re: Transmission switches to lower gear on it's own!
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Thanks so much, Gary. You've been a big help. As you probably know, another expert has been pretty firm on changing the input and output sensors first, possibly because of price. While I have checked the prices of those sensors, I haven't checked the price of the crank position sensor yet. I've done some research, and it seems that most people with my code 0725 do go the input and output sensor route first. It also seems that the majority don't find success until they change the crank position sensor, or worse, the TCM.
Given all this, do you still feel that starting with the crank position sensor is my best bet? Also, before I buy any sensors would you recommend that I look for corrosion or damage around all the sensors and their wiring? Thank you again...
Joe
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gsferraro
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Jun 10, 2015, 6:25 PM
Post #12 of 38
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Yes i would check all connections first. Just to let you know code P0715 is for the input speed sensor and code P0720 is for the output speed sensor. You dont have either of those codes. You may even want to clear the codes and drive it after you clean the connections. Gary
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joezapp
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Jun 10, 2015, 8:36 PM
Post #13 of 38
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Re: Transmission switches to lower gear on it's own!
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Thanks, Gary. Great info. I will be examining these connections this weekend. If nothing looks amiss I will be ordering the crank position sensor. I'll be back in touch soon. Have a great weekend! Joe
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gsferraro
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Jun 11, 2015, 3:06 AM
Post #14 of 38
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Re: Transmission switches to lower gear on it's own!
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Joe
If you do feel you need to change the sensor, pick up the new one first and look at it, if the sensor has a slot where the bolt goes the height has to be adjusted correctly or the car will never work right(meaning you cant have to much or to little air gap).
Sometimes on these cars the sensor gets stuck in the bellhosing due to corrosion. Gary
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Hammer Time
Ultimate Carjunky
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Jun 11, 2015, 3:07 AM
Post #15 of 38
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Re: Transmission switches to lower gear on it's own!
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I'm a little confused here on how a Crank sensor can be your shifting problem. The engine can't run without a working Crank sensor.
I realize the TCM may use the Crank sensor for an input but wouldn't the issue have to be with the wiring between the sensor and the TCM?, not the sensor itself because the car is running.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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gsferraro
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Jun 11, 2015, 10:20 AM
Post #16 of 38
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Re: Transmission switches to lower gear on it's own!
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Not really a shifting problem, its just dropping into limp mode from something that the tcm is seeing. Yes, car cant run without it, thats why i would clean the connections first clear the code and drive it to see what happens. According to joe thats the only code that the tcm is producing.
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Hammer Time
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Jun 11, 2015, 1:38 PM
Post #17 of 38
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Re: Transmission switches to lower gear on it's own!
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Right, but my point is that it really can't be the sensor itself because it is speaking to the PCM just fine. It's only the signal to the TCM that is a problem so I would expect a wiring issue between the sensor and the TCM.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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gsferraro
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Jun 11, 2015, 2:57 PM
Post #18 of 38
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Re: Transmission switches to lower gear on it's own!
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Yes, you are correct, as long as the engine is running ok. Technically it should be scoped to see what is happening to the signal, not sure if that can be done.
Ive seen some crazy stuff with these units and those crank sensors
(This post was edited by gsferraro on Jun 11, 2015, 5:01 PM)
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Discretesignals
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Jun 11, 2015, 5:32 PM
Post #19 of 38
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Re: Transmission switches to lower gear on it's own!
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I read on IATN about someone that had that same code on the same vehicle. They scoped the crank signals to both the PCM and TCM. The signals had good looking square waves, but the amplitude of the signal was only 4 volts on and off when it should have been 5 volts on and off. They tested the supply, signal ref, and ground and they were good. The crank sensor pulls the 5 volts to ground. It was enough not to flag a trouble code in the ECM for a crank sensor fault or to cause the engine to stall, but it wasn't enough to keep the TCM happy. They replaced the crank sensor and it solved their issue.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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joezapp
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Jun 15, 2015, 11:08 PM
Post #20 of 38
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Re: Transmission switches to lower gear on it's own!
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Thanks, guys. Yes, I've noticed online that changing the crank sensor does indeed sometimes resolve the 725 code. I'll be hoping for the same good fortune if the wiring between the sensor and the TCM seem OK. If I think that I may not be able to position the sensor perfectly, I'll have my mechanic do it. I'll report back. Thanks!
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gsferraro
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Jun 16, 2015, 4:05 PM
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Re: Transmission switches to lower gear on it's own!
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Yes, that air gap has to be correct, i have spacers that i grease on the end of the sensors. Gary Let us know how it works out.
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joezapp
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Jun 21, 2015, 8:08 AM
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Re: Transmission switches to lower gear on it's own!
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Hi Gary. It turns out that viewing the wiring and connections on this car is a difficult task. My mechanic attempted, but then said that it would be best to go to a transmission shop and get the free check that you suggested before going any further. I've got a free check scheduled Monday at Lee Myles. I'll come back with TCM codes and the c.v.i. volumes. Thanks, Joe.
(This post was edited by joezapp on Jun 21, 2015, 8:09 AM)
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gsferraro
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Jun 21, 2015, 11:04 AM
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Re: Transmission switches to lower gear on it's own!
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Ok, sounds good. c.v.i shows internal wear on the clutch packs. Gary
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joezapp
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Jun 22, 2015, 2:29 PM
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Re: Transmission switches to lower gear on it's own!
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Hi Gary. I went to Lee Myles today, and even though I had already told the manager on the phone on Saturday that I had code 725, he said today that if I already know that, then there are no other codes to find. He said that is the TCM code. Anything beyond that is diagnosing and repairing at $95/hour. I called another Lee Myles and was told the same thing. I really thought that the TCM would have other 2-digit codes in it, but both men said "no". Would you expect more information on a free check?
If not, the next step would be to change the crank position sensor and hope that the TCM just doesn't like the current sensor, since the wiring and connections are very difficult to examine on this car. I have the Transmission Service Manual for this car, and of the five possible causes for 725, one is battery voltage, but I checked that and we can rule that out.
Thanks, as always!
Joe
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gsferraro
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Jun 22, 2015, 5:16 PM
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Re: Transmission switches to lower gear on it's own!
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Joe,
I certainly do more on a free check, at least road test it, look at live data to see if anything looks out of place. I also lift the cars up and check underneath.
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