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Code P1684

Tiny
MAT2020
  • MEMBER
  • 2003 DODGE CARAVAN
  • 3.3L
  • V6
  • 2WD
  • AUTOMATIC
  • 155,342 MILES
I recently got a p1684 code that popped up, and the odometer keeps rolling when the engine works. Also if I put my transmission in reverse or drive the speedometer will go up to 40 KM/H (which is about 24 MPH). I was told to replace the TCM which I have done, hoping it would solve the problem but after replacing it I still have the same problem what should I do? I need help.

Also, when the speedometer does what I mentioned earlier I have my foot on the brake pedal.
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Wednesday, August 12th, 2020 AT 2:14 PM

21 Replies

Tiny
MAT2020
  • MEMBER
  • 12 POSTS
Problem solved, I kept on looking for causes when I finally found what the trouble I had was. Turned out it was an axle that broke at the joint, but the part that connects in the transmission, hence the mileage reading I was getting when I shifted in reverse or drive. It's the first time I see an axle break on that end instead of the other but still that's where the problem was. :-)
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Thursday, August 13th, 2020 AT 8:01 PM
Tiny
DANNY L
  • MECHANIC
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Hello, I'm Danny.

Thanks for sharing what you found. That might help someone in the future if they experience the same symptom. Thanks for using 2CarPros and hope you will use our site again in the future.
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Friday, August 14th, 2020 AT 12:16 AM
Tiny
MAT2020
  • MEMBER
  • 12 POSTS
Hi Danny,

It happens to be a combination of troubles that I have with my caravan. Turns out I was right about the axle but after I put another one on it kept on doing the same thing it did in the beginning. So after multiple checks I found out the gears in my transmission are done for, so now I need to put in a new transmission and since I don't know how to repair this one because I've never opened a transmission before and I'm afraid that if I try that I'll make it worse than it already is, I'd rather just spend some money and get a new one and put it in.
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Friday, August 14th, 2020 AT 5:10 PM
Tiny
DANNY L
  • MECHANIC
  • 5,648 POSTS
Hello again.

Well now days most transmission shops won't take transmissions apart to just replace a few parts. Now they just tell you they will only rebuild or not touch. Just be sure to get a good warranty when spending a few thousand on a rebuild or rebuilt replacement. Hope this helps and thanks again for using 2CarPros.

Danny-
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Sunday, August 16th, 2020 AT 12:26 AM
Tiny
MAT2020
  • MEMBER
  • 12 POSTS
Hello Danny,

Let me try to explain in details the exact problem I have with my transmission, then maybe you will be able to guide me in what kind of repair I need to do.

When my engine is running idle, my odometer that indicates how many kilometers I did since the last gas refill keeps on advancing and the transmission is on park position. If I put my transmission on reverse or drive and keep my foot on the brake pedal my speedometer automatically goes to 30 KM/H (about 24 MPH). If I let go of the brake pedal my right wheel will turn and when I apply speed (with whole front in the air) I hear some kind of a funny noise coming from under the van where the axle plugs in the transmission. So before I spend money on a new transmission I'd like to know what other tests I can do to try to solve my problem.

Thank you
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Sunday, August 16th, 2020 AT 10:57 AM
Tiny
DANNY L
  • MECHANIC
  • 5,648 POSTS
Hello again.

Okay, first I need to know about the odometer in your dash. Is it a mechanical or digital readout? Also, is the speedometer when it rises to 24 mph is that mechanical or digital as well? When you hear the clicking sound in the front CV axle that is an entirely different issue. We will get to that a little later. Can you take a video using your cell phone of this odometer-and speedometer issue and upload it here? Get back to us with this information and we can help figure this issue out. Thanks again for using 2CarPros and hope this helps.

Danny-
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Monday, August 17th, 2020 AT 6:23 AM
Tiny
MAT2020
  • MEMBER
  • 12 POSTS
Hello Danny.

Here's the video you requested, hope it works and you see it good. If you need more information let me know.

Thank you.
Video (Click to make bigger)
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Monday, August 17th, 2020 AT 8:31 PM
Tiny
MAT2020
  • MEMBER
  • 12 POSTS
By the way sorry about the video quality, I'm not an expert in filming. I just reviewed the video after I uploaded it and I made it badly. I hope you still can see good.
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Monday, August 17th, 2020 AT 8:43 PM
Tiny
AL514
  • MECHANIC
  • 4,105 POSTS
Hello, just to add a thought. I've seen a bad speed sensor cause the speedometer issue, and also check the alternator for any ac voltage coming out, bad diodes in the alternator will cause ac voltage to ripple through the system and the vehicle's ECM will go wacky. Here's the test for ac voltage. Just to verify the alternator isn't at fault.
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Tuesday, August 18th, 2020 AT 7:42 AM
Tiny
MAT2020
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I thought about the speed sensor as well, and some people even told me about the transmission solenoid. As for the alternator it's a brand new one that I put in a year ago.
Thanks for the tip. :-)
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Tuesday, August 18th, 2020 AT 8:44 AM
Tiny
DANNY L
  • MECHANIC
  • 5,648 POSTS
Hello again.

Just a few quick questions. You say you replaced the TCM -transmission control module. Was it a factory Dodge brand replacement? Also, when the trip meter is registering additional mileage when in park like your video shows does the actual vehicle odometer add mileage as well? This might not be a transmission problem but a PCM - power-train control module issue. Let me know and I'll get back to you. Thanks again for using 2CarPros.

Danny-
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Tuesday, August 18th, 2020 AT 9:46 AM
Tiny
MAT2020
  • MEMBER
  • 12 POSTS
Hello Danny,

Yes, my whole front is presently jacked up in the air. I had to in order to replace the TCM and my right CV axle. Now as for the rotation only the right wheel turns, but I haven't noticed if the left one does as well.

Thank you.
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Tuesday, August 18th, 2020 AT 10:09 AM
Tiny
MAT2020
  • MEMBER
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Sorry I forgot part of your question. The TCM I replaced come from another caravan I picked up in a scrap yard, otherwise I would have had to pay $678 for one from dealer. As for the odometer, it does continue to advance (so to speak) when the transmission is engaged.

Thank you again
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Tuesday, August 18th, 2020 AT 10:14 AM
Tiny
DANNY L
  • MECHANIC
  • 5,648 POSTS
Hello again.

So just to clarify both the trip meter and the odometer both add mileage when the car is running in park at the same time with foot on the brake? Let me know and we'll go from there. Thanks again for using 2CarPros.

Danny-
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Tuesday, August 18th, 2020 AT 11:14 AM
Tiny
MAT2020
  • MEMBER
  • 12 POSTS
Hello Danny.

I just went to confirm the question you were asking me and yes, both the trip and odo meters keep on advancing when engine idles. On top of that my check engine turned on while making the verifications. One is P1684 which is the TCM code and the other one is P0456. Hope this can help you in the diagnosis.

Thank you
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Tuesday, August 18th, 2020 AT 11:53 AM
Tiny
DANNY L
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Hello again.

I was made aware that installing a used or non Dodge factory TCM - transmission control module will cause a bunch of problems. The TCM is programmed with your VIN -vehicle identification number for your specific vehicle. The issue you are having with the mileage is 1 of 2 possible things. Number one is you have an internal fault in the transmission and number two is you are having an issue with the PCM- power-train control module. You will have to have a factory type professional scanner to retrieve data to find where the fault is coming from within these 2 components. Hope this helps and thanks again for using 2CarPros.

Danny-
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Wednesday, August 19th, 2020 AT 3:38 AM
Tiny
MAT2020
  • MEMBER
  • 12 POSTS
Hello Danny.

I got another comment from Al 514 about having my alternator checked because it may be at fault as well. The diodes in it may cause some kind of a power surge that makes my speedometer go bezerk. So I looked into the matter, made more researches on internet and tested something on my vehicle. When I get the engine started there's a funny whining kind of noise that I hear in the engine. So I disconnected a simple wire on the alternator and the noise stopped. So I'll start by removing the alternator and have it checked by a mechanic that is better equipped than I am to do that test. Is it normal that I can have a failing alternator even if it's a year old? I replaced it in January of 2019! Now here's a question: is it safe for me to try driving my van to bring it to a mechanic to have a scanner plugged in to take care of the trouble codes I mentioned?

Thank you.
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Wednesday, August 19th, 2020 AT 5:13 AM
Tiny
DANNY L
  • MECHANIC
  • 5,648 POSTS
Hello again.

It is always a possibility to have stuff that is relatively new fail or become defective. I've seen it happen. You should be alright to drive the van to a local shop to have a scan taken. Hopefully they can find the problem within the transmission or the PCM. Keep us updated as to what they find after scanning. Hope this helps and thanks again for using 2CarPros.

Danny-
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+1
Wednesday, August 19th, 2020 AT 6:34 AM
Tiny
MAT2020
  • MEMBER
  • 12 POSTS
Hello,

Here's a quick update on my trouble I had with my van: I got busy and didn't have the time to post an update on the progress I had made on my repairs. So after removing the alternator on my van I took it to mt mechanic that tested it and it was the diodes in it that were done for. So I had it fixed and then I put it back on my van and since everything is going good. I have no more issues whatsoever regarding that problem. I'd like to thank you Danny for trying to help me out as well as Al 514 for his idea of making me having my alternator checked. If I have issues with another mechanic job I'll be sure to come on this site and have a chat with you guys to help me out.
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Sunday, September 13th, 2020 AT 10:05 AM
Tiny
AL514
  • MECHANIC
  • 4,105 POSTS
We're glad to help, the alternator putting out ac voltage can do weird things. I always check them first in a situation like this. Voltage level correct and no ac ripple coming from it.
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Sunday, September 13th, 2020 AT 3:17 PM

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