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Discussion Starter · #1 · (Edited)
I stumbled across this today on my 2011 R/T Classic

A few weeks ago I did my P01 Timing Recall myself and found that the thermostat was bad. Well, I say bad, the rubber seal(s) on the thermostat (top and bottom) had separated from the thermostat. Not the thermostat housing seal. So to keep the car running until I ordered a new 180 degree T-stat, I removed the rubber so it did not get into the radiator or water pump. Now I've drove the car a few times to work since then, and it set a CEL, three in fact. Temp out of range, Temp too low, and temp permanent all are P0128. The car takes about 20 miles to reach 190 degrees due to the little holes in the thermostat where the rubber was, and this lets the coolant bleed thru the T-stat. The T-stat still works like it is suppose to at the correct temp.

Now I stopped and cleared the codes once last week when it first set them and they came right back as the T-stat has not been changed yet. My wife has drove it a few times as I told her it would be OK around town. Today I drove it around and the ECO light is not on and the MDS is not active even though the engine temp it still running at 190 degrees. Car is in automatic mode and still does not go into MDS. I can put it manual mode and still shift it, then put in "D" automatic mode and MDS is still off! It does seem to come in when decelerating or not giving it gas while say coasting down a hill, you can briefly hear it cut back to V8 as soon as you mash the peddle again, but the ECO light never comes on with it.

Now this will leave the CEL light on due to the T-stat temp too low. Most of you may not want this, but its a way to cut the MDS off without a programmer. Car is still running very strong and not over heating in any way. I also noticed that it stays in the gears longer, especially 1-3 then seems to shift like a performance car should after that by going into 4th for a few seconds longer than before, and then into 5th or OD. It also down shifts much sooner than before also, seems like its trying to engine brake as well with your braking.

Now I do not plan to leave the car this way, I've just been lazy and not changed the T-stat yet, so I really don't know what effects this may have long term.
 

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MDS will not kick in until you’re up to temp. MDS also causes an engine to run cooler so on a cold day, MDS can kick in and out by operating temp as well as engine load.
 

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Discussion Starter · #3 ·
MDS will not kick in until you’re up to temp. MDS also causes an engine to run cooler so on a cold day, MDS can kick in and out by operating temp as well as engine load.
Well, that makes sense. I also noticed that it seems to cut the engine power somewhat as the car will now not pull as hard as before. So this must be a safety feature for a bad thermostat in the event that it sticks open.
 

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MDS will not kick in until you’re up to temp. MDS also causes an engine to run cooler so on a cold day, MDS can kick in and out by operating temp as well as engine load.
I'm curious, but where did your hear engine temp effects the MDS? From what I have seen, MDS troubleshooting does not mention engine temps at all.
 

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So a "fail to reach temp" CEL disables remote start until it's cleared? Learn something new everyday. Thanks
 

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I'm curious, but where did your hear engine temp effects the MDS? From what I have seen, MDS troubleshooting does not mention engine temps at all.
The PCM will activate the 4-cylinder mode when the following enabling conditions are met:

* Low engine load
* 1200 to 3000 rpm
* Vehicle speed between 12 mph and 90 mph
* Battery voltage from 9 volts to 15 volts
* Oil pressure from 15 psi to 147 psi
* Oil temperature greater than 120 F
* Engine coolant temperature from 158 to 248 F
* Ambient temperature from 14 F to 248 F
* No throttle position sensor or MDS faults
Still looking where I read that the engine temp actually drops in MDS mode and may drop enough to disengage the MDS. I think it was on a post here on CT but will be darned if I can find it. I think it was an official Mopar (Dodge) write up.
I've noticed that on my Jeep, it takes longer for the MDS to kick in when it is cold out than when it is warm out.
 

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Discussion Starter · #8 ·
Replaced the t-stat yesterday and cleared the CEL codes and the MDS and ECO lite are back on and working again. So I guess the temp too low code causes it to disable the MDS for sure. I noticed that the power has not been completely restored back to what it was before the t-stat set the code. I know I can not reset the "permanent" code and the ECU must do that after it confirms the issue has been corrected, and that's just a matter of driving it a few times. It did the same thing and set a permanent code when I forgot to plug the air temp sensor back in and started the car, then drove to the parts house to find out what the code was, felt stupid about that one. But after a few trips around town, the car had all its power back, and the permanent code was gone.
 
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