P1604 headache

Matthew Keller

Matthew Keller

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Joined
Apr 19, 2017
Messages
8
Location
Orlando, FL, United States
I can't seem to win with my TJ. Just fixed a few issues and now I'm throwing a p1604 code. This is a communication issue apparently with the computer.

I just completely removed and cleaned my throttle body and IAC so I'm thinking something during that processes may have caused this problem. The first time after installing the throttle body back on everything seemed fine, idled fine took it around the block and it was ok. Second time firing up it had this crazy idle issue where it literally sounded like my Jeep was breathing. The third time I threw the p1604 code. I've reset the battery twice and it came back immediately.

2005 TJ Auto 104K

Any thoughts or insights would be really appreciated.
 
Found this elsewhere on the interwebs...

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P1603-PCM INTERNAL DUAL-PORT RAM COMMUNICATION

WHEN MONITORED: Ignition off, on, and run/start.

SET CONDITION: Internal PCM failure detected. Intermittent open on PCM Connector 1, pin 12, (F11) Fused Ignition Switch Output circuit.

POSSIBLE CAUSES: PCM fused ignition switch output circuit or PCM.

***********

You could have a bad PCM, a bad connection, a broken wire somewhere or even a bad ignition switch.

A bad PCM is challenging to prove in some cases. Even veteran techs are known to eliminate all the other possible causes and condemn the PCM last by proving all else is good. Internal electronics are near impossible test as they require special equipment and more importantly information to test them which is NOT provided by the manufacturer to the public.

Start with what you can test first and prove whats good.

Locate a pinout digram for connector 1 and inspect pin 12. Look for corrosion, discoloration or looseness in the connector. Clear the codes, start it and try wiggling the wire that goes to pin 12. See if you can induce a code. It takes more than one failure to set the code so it may come back as a pending code the first time you recreate the failure.

Try locating a wiring diagram for the ignition switch. Wiggle test the wire that is the output from the ignition switch and goes to the PCM circuit. Look for any melted connections, discoloration or loose connections. Same thing with pending code applies. May need to fail more than once to set a hard code and illuminate MIL (Malfunction Indicator Lamp).

Locate fuse that protects the switched ignition circuit to the PCM and check connections there.

You may need to check all the wiring and connections (plugs) in the entire circuit to eliminate those possibilities.

You have an advanced level diagnostic to perform and it will take a lot of hard work and patience to perform.
 
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Check all the wiring coming from the PCM. Make sure none of it is rubbing anywhere or has any damage to it whatsoever that could be causing things to short out.

9 out of 10 times I hear about this code, it seems to end up being a faulty PCM.
 
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Be sure to closely examine the wiring harness that bends around the vertical stud at the rear of the engine's valve cover. The threads on that stud are known to rub through the wiring insulation and cause intermittent shorts to ground causing extremely difficult to troubleshoot electrical problems.
 
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Thank you all for your messages! - Heres my thoughts - this happened after I did the following work:

1. Washed engine bay
2. Replaced Coil Pack (2005 doesnt have distributor)
3. Replaced spark plugs
4. Cleaned throttle body and IAC
5. Replaced TPS

It happens IMMEDIATELY after reset. I did a 8+ hour hard reset and it happened immediately, like 2 seconds after start up still in park so I'm thinking that a wire got messed up somewhere.

Does anyone have the pin diagram for the 2005 PCM or a wire harness guide? I want to go over all of the wires before I surrender it for a $1000+ PCM repair.
 
Jerry Bransford said:
Be sure to closely examine the wiring harness that bends around the vertical stud at the rear of the engine's valve cover. The threads on that stud are known to rub through the wiring insulation and cause intermittent shorts to ground causing extremely difficult to troubleshoot electrical problems.
Click to expand...

Thank you for the insight! I'm going to have to check there. I ordered a multimeter and a 12V circut tester and I guess I'm just going to have to follow all of the wire and look for a short.
 
I'm still dealing with the issue. Currently having someone rebuild mine. - What I would recommend 1000000% first is to perform the diagnostics that Jeep provides first. This will isolate the issue 99% of the time. If you want to email me at [email protected] I can send you the PowerTrain manual which outlines the procedure. You just need a 12V test light you can get off amazon super cheap.
 
RE-resurrectting this because I am currently having the exact same problem on my 06 TJ 4.0 Auto. I’ve been getting P1604 and P1603. Been to 4 different shops including the dealership, and they all say it’s a bad pcm. Who did you send out your pcm to? What’s the best solution for this problem as of 2018? It seems to be very common for 05-06 Tj’s
 
Raheeeelio said:
RE-resurrectting this because I am currently having the exact same problem on my 06 TJ 4.0 Auto. I’ve been getting P1604 and P1603. Been to 4 different shops including the dealership, and they all say it’s a bad pcm. Who did you send out your pcm to? What’s the best solution for this problem as of 2018? It seems to be very common for 05-06 Tj’s
Click to expand...

It very well could be the PCM.

See this thread: Where to get a new or rebuilt PCM?

For a replacement PCM, I suggesting getting ahold of @Wranglerfix. The PCMs they sell are guaranteed to work!
 
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Hello all,

I know this is an old post, but I have a feeling it may still be relative to some, as it is to me. I wanted to re-re-resurrect this thread because here I am, 6 months later with the same PCM problem. I wanted to ask if anyone here has had this problem resolved or knows of a way? Because I am nearly ripping my hair out and unfortunately starting to grow a hate for my beloved TJ. I had my car diagnosed by 3 different Jeep dealerships, all of them said my PCM was bad and needed to be replaced. They said they could get one from a third-party company for a hefty price of about $1500. I decided to try local options first. I tried having my PCM sent out for a rebuild by 2 different local shops, only to have it sent back because it apparently “could not be done”. I bought one off eBay that was “guaranteed” to work, only to have that one give me completely different codes, and made the car totally undriveable. Tried to send it out with NAPA, it was sent back to us again, cause it couldn’t be done. Autozone claimed they had seen this exact problem before and guaranteed that they could fix it and it would work. I’m sure you can take a guess with what happened on this try. Still same check engine light with same codes. My only other options are try to @Wranglerfix (which I think is my next option), try the dealer, or sell the car.....if I can. So if anyone has ANY advice, I could really use it. Thank you very much.
 
After writing my post right before this, I went to look at @wrangler6035’s profile. I realized he works with FlagShip One Inc, which is actually the company that I bought my PCM off eBay from. Everyone else seemed to have a great experience with them except for me. I was actually very disappointed and displeased with them. They never responsed to neither me nor my father’s calls and emails, trying to express how the PCM they sent us did not work. After about a 2 week haggle with them, they finally refunded our purchase, but decided to keep a percentage for a restocking fee. Even though their supposed PCM was “guaranteed” to work.... Definitely not going to do business with them again. So now I’m very desperate. If someone could please shine some light on this, I’d appreciate it!!
 
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Raheeeelio said:
After writing my post right before this, I went to look at @wrangler6035’s profile. I realized he works with FlagShip One Inc, which is actually the company that I bought my PCM off eBay from. Everyone else seemed to have a great experience with them except for me. I was actually very disappointed and displeased with them. They never responsed to neither me nor my father’s calls and emails, trying to express how the PCM they sent us did not work. After about a 2 week haggle with them, they finally refunded our purchase, but decided to keep a percentage for a restocking fee. Even though their supposed PCM was “guaranteed” to work.... Definitely not going to do business with them again. So now I’m very desperate. If someone could please shine some light on this, I’d appreciate it!!
Click to expand...
Give Mark a call from Wrangler Fix.
+1 (954) 803-8829
I just ordered one from him and they showed a video on what they did and found, and now they are selling them. He claims he 100% fixed the issue. Tell him Wyatt sent you. Comes with all the regular warranties. It’s was like $560 shipped. When I get the unit in the next few days I’ll let you know how it worked for me.
 
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Wyatt Morris said:
Give Mark a call from Wrangler Fix.
+1 (954) 803-8829
I just ordered one from him and they showed a video on what they did and found, and now they are selling them. He claims he 100% fixed the issue. Tell him Wyatt sent you. Comes with all the regular warranties. It’s was like $560 shipped. When I get the unit in the next few days I’ll let you know how it worked for me.
Click to expand...

I will definitely try that. Have you received the PCM yet?
 
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I don't think the OP came back to confirm a PCM rebuild fixed his issue I'm in this same situation now and can't pass emissions until I get it fixed on my 2005 TJ Unlimited (LJ) with the 42RLE.

So my code stack is a P1604 as a current fault and Pending are P0613 and P0700 . My jeep has been throwing intermittent codes for about 4 years. They come, they go, they come back. Sometimes I disconnect the battery to clear them, they come back. It hasn't affected how the jeep drives and shifts. 3 years ago I had the dealer replace the transmission and I haven't had any transmission or shifting problems.

I'm going through my wires now. What I really need is a pin out diagram for the TCM. Pretty sure I found one for the PCM on Youtube but I'd be more comfortable with a actual manual page. I'm looking for an intermittent short now and the PIN diagrams are key to that.

Any help would be appreciated
 
leoparddog said:
I don't think the OP came back to confirm a PCM rebuild fixed his issue I'm in this same situation now and can't pass emissions until I get it fixed on my 2005 TJ Unlimited (LJ) with the 42RLE.

So my code stack is a P1604 as a current fault and Pending are P0613 and P0700 . My jeep has been throwing intermittent codes for about 4 years. They come, they go, they come back. Sometimes I disconnect the battery to clear them, they come back. It hasn't affected how the jeep drives and shifts. 3 years ago I had the dealer replace the transmission and I haven't had any transmission or shifting problems.

I'm going through my wires now. What I really need is a pin out diagram for the TCM. Pretty sure I found one for the PCM on Youtube but I'd be more comfortable with a actual manual page. I'm looking for an intermittent short now and the PIN diagrams are key to that.
Click to expand...
Update from years later: I ended up getting a PCM from Wrangler Fix. solved all the issues, drove the LJ for about another year before selling it. 100% recommend
 
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