42RLE: P1776 code and temp at 1200 degrees

LJ Jim

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All,

I have a new to me 2006 wranlger unlimited with 141k. Drove it 600 miles home with no problems. Now the auto trans keeps going into limp mode but still works well otherwise. Codes p0700 and p1776.

My trusted, but not a jeep expert, mechanic says scanner shows trans temp jumps from 120 to 800 to 1200 degrees. He says I need a new pcm.

Based on the ambient temp and trip duration before it throws codes, I suspect it is a temperature or percieved temperature problem.

Temp gauge is steady at 210.

Flushed trans and disconnected battery, no help.

Has anyone had this problem?

Any help is greatly appreciated.

Jim
 
I don't even know if a trans temp sensor exists, but that sure looks like a bad sensor or an intermittent short to me. 1200 is ridiculous. That's up there where aluminum starts to melt.
 
1200 degrees? Wow, something is wrong there.

How did he determine it needs a new PCM? Did he perform any diagnostics on the PCM itself?

There is of course a chance it needs a new PCM, as the 05-06 models have the TCM and ECM in one unit (the PCM), as oppose to the earlier models which had a separate TCM.
 
I picked it up today. Mechanic verified the transmission temp sender was working properly and that at start up the PCM was reading temp correctly. Then as the system warmed up the sensor continued to send correctly but the PCM started to read the temp wrong.

Going to get a second opinion before I jump off the new PCM cliff.

Still looking for anyone that's had this issue.

Thanks.
 
Does it really need that sensor? What does the PCM alter from the transmission temperature? I wonder if you could run the sensor in free air and never reach the temperature that freaks out the PCM? What temp does it start to read false temperature?
 
On the 05/06 the TCM is Integrated into the PCM. The PCM uses the readings from the trans temp sensor to adjust shift patterns and it also uses it to determine Limp Mode. The FSM has values (ohms or Volts- can't remember which) for the output range of the sensor so you can test the pin out. Unfortunately trans temp codes are a common symptom of a failing PCM. Usually it's codes p0714 and p0218.
 
Maybe not allowing the PCM to see the trans temp sensor at all could be a stop gap measure. The engineers added a strategy for temp sensor failure. Removing the wire from the connector might be an option. This is from the service manual.

CALCULATED TEMPERATURE A failure in the temperature sensor or circuit will result in calculated temperature being substituted for actual temperature. Calculated temperature is a predicted fluid temperature which is calculated from a combination of inputs: • Battery (ambient) temperature • Engine coolant temperature • In-gear run time since start-up
 
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Thanks guys. This was the info I was hoping to get.

My second opinion shop let me down, they just wanted to pull the trans and disassemble.
 
I have been dealing with trans issues myself and during my research I found some prior posts about the temp sensor. I remember a post that had your issue and he checked a transmission temp sensor ground that is connected at the rear of the Cylinder head. He checked the cable at that point and found the wiring was a bit chaffed. As I recall he was able to correct the problem addressing the wiring and ground there.