P1281 code, Cold Engine=OD unlocking? - JeepForum.com
 
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post #1 of 6 Old 09-21-2017, 10:28 PM Thread Starter
GOLDWING
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P1281 code, Cold Engine=OD unlocking?

The title says it all.

I noticed that my temperature gauge has occasionally dropped the needle from the normal 210* to around 180*.

Today I felt the transmission unlock from OD a couple of times at 55 to 65 MPH.
It wasn't under acceleration where I would expect a downshift and my T/V cable is adjusted per FSM specs.

I scanned the codes and it turns out that there was a p1281 logged. The description said that the temp was too low for too long.

I am going to replace the thermostat tomorrow and see if it makes any difference.

Will a cold running engine cause the PCM to make the transmission to act badly?

GW


2 '98 4.0 ZJs
Hers is stock, mine, OME shocks, BB, Aussie, 2x6 sliders, 31s, etc.
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post #2 of 6 Old 09-22-2017, 01:38 PM
kg6mov
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Yes, if the engine is under temp the computer will do strange things to try and get it back up, and that will include unlocking the converter.


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post #3 of 6 Old 09-22-2017, 02:05 PM
Timo_90xj
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Are you sure that low engine coolant temp will cause TC lockup disabled situtation? As far as I know, that feature was introduced on WJs/ KJs, or even as late as WKs?

Living here in cold climate, I've always gotten OD on and TC lockup as soon as tranny fluid temp is up to when OD/ TC lock up should engage (IIRC above 0* Celcius according to tranny temp sensor).
It's normal for the OD and TC lockup to engage before the engine temp gauge even starts to creep up when it's below freezing temps.

On the other hand, it can take up to 30 minutes of highway driving on really cool days for the OD and/or TC lockup to engage.

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post #4 of 6 Old 09-22-2017, 05:23 PM Thread Starter
GOLDWING
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The temps were in the high 80s yesterday when it started unlocking the OD. As I said above, engine temp was 170*-180*. I installed a new Stant 195* thermostat this morning and took Jeep Girl and Jeep Dog for a four hour ride on both highway and trails. No more unlocking in OD.

$10, 1 hour fix. I'm not sure how the PCM "thinks", but I am glad that the code reader and the PCM pointed me in the right direction in the first place.

GW

2 '98 4.0 ZJs
Hers is stock, mine, OME shocks, BB, Aussie, 2x6 sliders, 31s, etc.
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post #5 of 6 Old 09-22-2017, 09:49 PM
Timo_90xj
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Well that's good to know. Weird that there's no mention of this at all in FSM or ATSG repair manual.

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1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***

***Under construction***
1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***
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post #6 of 6 Old 09-22-2017, 10:28 PM Thread Starter
GOLDWING
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Quote:
Originally Posted by Timo_90xj View Post
Well that's good to know. Weird that there's no mention of this at all in FSM or ATSG repair manual.
Check out 25-11 in the FSM. There is some good info. I read it to say that it is hard to predict what one sensor will cause the PCM to tell the next sensor or servo to do.

In my case (I assume) it was telling my transmission that I needed higher R.P.M.s to get heat in the motor.

GW

2 '98 4.0 ZJs
Hers is stock, mine, OME shocks, BB, Aussie, 2x6 sliders, 31s, etc.
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