Need help solving this one. Limp mode + P1605. TCM?

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Posts: 13
Joined: Sun Oct 15, 2017 6:05 pm
Car: 99 I30

Need help solving this one. Limp mode + P1605. TCM?

Postby branden0502 » Sun Oct 15, 2017 6:45 pm

Hey everybody, Thanks in advance for any help you give. Ill try to give as much information as I can.

1. My alternator went out. I was quite a ways from home to I had to drive it until the battery went dead, and I had it towed the rest of the way.

2. I replaced the Alternator, started the car and showed 14v at the battery. The next day I started the car and the alt was not working again. I took back out and up to Autozone to have it tested, it was good.I started checking fuses and noticed that i had a blown eng mgt fuse. both sides terminals showed 12v(short somewhere) I tried looking it up but couldn't find out what that fuse did. to many conflicting answers. I noticed that my battery wasn't holding a charge, so i took it to have it tested and it was bad.

3. I replaced the battery, put everything back together and boom...14v at the battery. not sure how a bad battery cause the alt not to at least show it was charging, but hey, it worked. the eng mgt fuse was still shorted, but everything seemed to work.

4. i drove the car aroung town for 2wks with no issues.

5. I took a trip out of town, about 400miles into it my belt broke. it was 1am and had to be in Ny in the morning and still had about 450 miles to go so i went to the nearest walamrt and picked up 3 batteries so i could just swap them out as they went dead so i could at least get there. Luckly all i lost was a/c and alt. about 350-400 miles later i lost engine power. the car started to just slow down. no matter how much gas i gave it, the rpm's wouldn't move. I was able to get pulled over and check the CEL, and got a p1605. Comm failure between the ECU and TCM. I had to get towed the rest of the way....$$$$$$$. I ran the Transmission self test from the service manual. Im not sure if i did it right or not because the o/d light just stayed on, which to me either means i did it wrong or from the SM, PNP switch, o/d control switch or throttle position circuit is dissconnected, or TCM is bad. Because of the P1605 code i ordered another TCM.

6. I replaced the belt, and ordered another TCM. installed both, and took the car for a test drive. It seemed to drive fine for a few miles, then the same issues. when it first started it would just take off slow and very slowly build up speed, but because of the speed limits in NYC i never really got over 40. after that i ran the Self test again, and it didn't seem to match any of the options in the SM.

7. I swapped the TCM back to my original, just to test it again. it seemed to be worse than with the other TCM. When i first started driving, it was like the other time, very slow to take off and would very slowly build up speed, then it got much worse.i could floor it and the rpms don't move. it wouldn't go over 10 mph. Then i figured out i could pump the gas over and over, not stopping, and i could get it up to about 30, just continually pumping the gas. I was about 10 miles from where I had to be do i didn't really have a choice to get it back. after that i ran the Self test again, i recorded it and linked the youtube video for other to verify. To me it is from the SM "all judgement flickers are the same" from the SM it looks like there is suppose to be one long flicker first, then the 10 judgement flickers. and if they are all the same, which that is how it looks to me, that is "all circuits that can be confirmed by self diagnosis are ok"

Thats where I am. I have also read that the P1605 code means the ECU is actually the problem. any thoughts or ideas would be awesome. I'm kind stuck on what to do. Im about 900 miles from home so dropping it off at a shop isn't really going to happen. at best I will fly home and come back to get it with a trailer. But I would love to be able to fix it here. Should I repace the ECU?

Thanks Guys
Last edited by EdBwoy on Mon Oct 16, 2017 12:02 am, edited 1 time in total.
Reason: Updated title

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Re: Need help solving this one. Limp mode + P1605. TCM?

Postby EdBwoy » Mon Oct 16, 2017 12:13 am

Hello and welcome to the forum.

I tell you, you've done most of what I'd do and then some. The one thing I haven't seen mentioned is unplugging & inspecting the TCM wires on the ECM end, and checking the trans wires and grounding points in the engine bay.
Also, for giggles, could you take a look at your crank pulley when your engine is off and also running to see if it looks healthy?

Have you had a chance to look at the FSM to see what the diagnostic steps could be?
Page 422 in the EC section: ... 998_I30/ec

Btw, I updated your title so that it gets more visibility in search results.

Posts: 13
Joined: Sun Oct 15, 2017 6:05 pm
Car: 99 I30

Re: Need help solving this one. Limp mode + P1605. TCM?

Postby branden0502 » Mon Oct 16, 2017 3:41 am

Edbwoy, thanks for the help and fixing the title.

As for the health of the crank, if you mean it's not loose and wobbly, yes, I have checked that

I plan in doing the check described on page 424 from that section of the fsm today. I'll post the results when I get them

Are there any specific wires tour talking about in the engine bay? I have checked the main ground from the battery to the block, and general connection of harnesses.


Posts: 13
Joined: Sun Oct 15, 2017 6:05 pm
Car: 99 I30

Re: Need help solving this one. Limp mode + P1605. TCM --SOLVED?

Postby branden0502 » Sat Sep 15, 2018 3:18 am

Finally got this fixed. Sometimes you feel like an idiot. The #1 cat had broken apart and all the pieces where in front of the #3 cat creating a huge block.

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