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Chris (aka - Moose)
Chris (aka - Moose), Technician
Category: Chrysler
Satisfied Customers: 48703
Experience:  16 years of experience
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Chrysler PT Cruiser: 2001 PT Cruiser, mis-firing while cruising

Customer Question

2001 PT Cruiser, mis-firing while cruising at constant speed. Four engine codes showing: P1684, P320, P300 & P1391.
Identical problem summer of 2014. Replacing Cam Sensor and Crank Sensor failed to correct. A second garage said short in a wiring harness and problem disappeared. Now it's recurring again after 9 months.
Same garage now says the P1684 code means the TCM is failing, but that is an expensive repair and won't correct the problem if there's a short.
What's going on here?
Submitted: 2 years ago.
Category: Chrysler
Expert:  Chris (aka - Moose) replied 2 years ago.
I am sorry for the delay in getting a response to you. Sometimes we get alot of customers and just can not keep up. Sometimes you just have to wait for the correct tech to login.Do you even still need help. Sometimes customers seek help elsewhere or figure it out on their own before we get to each and everyone.I am sure I can help a lot or a little at least something if you give me a chance and work with me. I am going to get an answer to you regardless if you reply or not sooner or later.If your concern is urgent reply and let me know and if you have anything more you think will help me, to help you, let me know. I work on here normally 3pm-3am central. Thanks Chris
Customer: replied 2 years ago.
Yes I still need help and no I haven't yet got an answer to what the problem is. The car is running and though the mis-firing is annoying, my real concern is to find the source of the problem before I find myself with a dead engine on a freeway or stranded miles from home.
Expert:  Chris (aka - Moose) replied 2 years ago.
Do you need or have you done the diag steps for these codes?1684 just means the computer has recently seen a battery disconnect. So that can be poor battery connections or high resistance in the wire pins to the PCM. Do you have a diagnostic tool that can monitor the cam and crank sensors while running and carefully wiggling there wire harnesses? You want a excellent 5 star answer & I would like to be rated the same for providing it. Consider I don't know your skill level & I can't see, smell, hear, or touch the vehicle. It may take a few back and forth replies. Try your best to respond with good detail so I can do the same. I normally log in at 3pm and work late. A rating is required. Your rating me, what I type. I am not an employee of this website, nor have control over the fees or the time it took to get a response. If you rate negative or not at all you still paid, but I get nothing. I want you pleased with me and my efforts, so let me know if your experience here has come up short.Thanks Chris
Customer: replied 2 years ago.
I have no tools and do not work on the car myself, but I've wasted a lot of money watching the mechanics I pay just chase their tails on this problem .... I need to be able to take it to someone and give them a strong lead so that I can get a reasonable repair.Last summer I paid for replacement of Cam and Crank sensors that was unnecessary and did NOT solve the problem. Now the one mechanic who did manage to make the problem go away for 9 months is saying that the P1684 code means that my computer is failing. There may be some basis for his saying that. After much googling of engine codes, I came across a page that says there could be several possible causes for the P1684 code (
1. Battery was recently disconnnected (but in my case, it was NOT)
2. Transmission Control Module (TCM) replaced or disconnected (NOT)
3. Faulty Transmission Control Module (TCM) (how to determine/ diagnose this?)
4. Transmission Control Module (TCM) harness is open or shorted (candidate cause?)
5. Transmission Control Module (TCM) circuit poor electrical connection (candidate cause?)But the above is from a Dodge engine page. I believe the PT Cruiser may share the same transmission as the Dodge Neon, but I need to know if the above 5 possibilities also apply to my PT. Can you verify that?Also, how to check for possibilities 3, 4 and 5 above, since numbers 1 and 2 do not apply.AND, what do the three other engine codes (P320, P300, and P1391) tell you about the problem?Thanks for your knowledge on the above.Bob Randall
Customer: replied 2 years ago.
The causes I mentioned relate to the TCM (Transmission Control Module). How is the TCM related to the PCM (Powertrain Control Module), or are they the same thing by different names?
Expert:  Chris (aka - Moose) replied 2 years ago.
Being that your not able to do diagnostics, what from me would help. Can you list out what questions you would like me to answer based on these codes. We can talk about the codes or what you read on google but none of that will solve the issues. Diag needs to be done.