Trouble Diagnosing Cause of P0128 Code - Jeep Garage - Jeep Forum

Go Back   Jeep Garage - Jeep Forum > Jeep Platform Discussion > Grand Cherokee - WK > Troubleshooting/Problems

Reply
 
Thread Tools Display Modes
 
  #1  
Old 01-22-2016, 08:05 AM
Member
My Jeep: 2006 3.7L WK
 
Join Date: Mar 2015
Location: Cincinnati, OH
Posts: 14
Thanks: 1
Thanked 0 Times in 0 Posts
Rep Power: 823
twolfcorner2009 is on a distinguished road
Trouble Diagnosing Cause of P0128 Code

I'll try to keep this short:

-I'm on my 3rd Thermostat in the last month (Original Thermostat I thought went bad and was stuck open, replaced it with one that didn't solve the Jeep from throwing the code, then put another one in and it hasn't solved the problem).
-I replaced the Coolant Temperature Sensor to see if that was the problem. It apparently wasn't.
-My 06 Grand Cherokee will get up to the first mark on the temp gauge in the dashboard if I start it and just let it idle in the morning after about 10-15 minutes regardless of the outside temp (whether it's the single digits it has been this week or it's 70 degrees like when it's in the summer).
-I drive 20 miles to work on the interstate and by about the end of the first mile, engine temp read out is ~100-115 degrees as read by my scan tool and the needle on the temp gauge is essentially sitting on the post that right on top of the C.
-Now, after running at 70-80mph for 5-10 miles, I usually hit stop and go traffic and my engine will get up to the 180+ degrees after sitting in that for a few minutes.


What in the heck could be going on here? I have a hard time grasping that it's possible to get 2 brand new thermostats that are both bad, back to back. Any insight is appreciated!

Reply With Quote
Sponsored Links
Advertisement
 
  #2  
Old 01-22-2016, 03:34 PM
Member
My Jeep: 2006 3.7L WK
 
Join Date: Mar 2015
Location: Cincinnati, OH
Posts: 14
Thanks: 1
Thanked 0 Times in 0 Posts
Rep Power: 823
twolfcorner2009 is on a distinguished road
Re: Trouble Diagnosing Cause of P0128 Code

Update:

So, i monitored my engine data during the commute home today. I did 5 minutes of city driving before getting on the highway and cruising at 70-80mph for the next 20 minutes. Here are some temps:

-Entering on ramp for Interstate: 136 degrees

I then drove ~17 miles at Interstate Speeds

-Getting into exit lane for my exit: 118 degrees
-Coming to a stop at the end of the exit ramp: 138 degrees (exit ramp is maybe a 1/4 mile long)
-Turning into my apartment complex a 1/2 mile down the road from the exit ramp stoplight: 158 degrees
-Parking at my apartment (maybe 1/8 mile from the entrance to the complex): 171 degrees

It never climbs past the thermostat regulating temperature, but it climbs INSANELY fast when I go from driving on the highway to city/residential driving. I literally drive on the highway with my temp needle sitting on C. Hope this helps diagnose it, I'm at a loss.
Reply With Quote
  #3  
Old 01-22-2016, 07:25 PM
Senior Member
My Jeep: 2006 5.7L WK
 
Join Date: Dec 2009
Location: Home of the Mountain Blue Bird
Posts: 1,340
Thanks: 0
Thanked 73 Times in 61 Posts
Rep Power: 156251
jeepgcoman has a reputation beyond reputejeepgcoman has a reputation beyond reputejeepgcoman has a reputation beyond reputejeepgcoman has a reputation beyond reputejeepgcoman has a reputation beyond reputejeepgcoman has a reputation beyond reputejeepgcoman has a reputation beyond reputejeepgcoman has a reputation beyond reputejeepgcoman has a reputation beyond reputejeepgcoman has a reputation beyond reputejeepgcoman has a reputation beyond repute
Re: Trouble Diagnosing Cause of P0128 Code

I am not that familiar with the 3.7, so I'll just speculate a little. When does the cooling fan kick in? Does the 3.7 have a viscous fan, an electric, or a hydaraulic fan? If the vehicle is slow to warm up, the PCM should be tripping a MIL. It calculates how long it should take to warm up and, if it doesn't meet those parameters, it will trip the MIL. Sometimes that will happen too if the installed thermostat opens at too low of a temperature. Also, are you putting the thermostat in correctly?
__________________
05 LX/RT & 06 WK/GCO, modded similarly, MDS "ON" Light, Vortex Gens, Debadged, DashHawk, BT Catch Can, SRT CAI W/Add Air Inlet, K&N Filter, Sonnax Trans Press Booster, SC Tuner W/Adv Trans Tuning App, DS Tuner, Cust tube headers w/3 in. catback, Bilsteins, SRT frt/rear bumpers, Eibach SRT Lwr Sprgs & Sways, FRI Sidewinder Cam Adv 2*, 6.1 valvetrain, SLP 25% UD Pulley, BBK 90mm TB, SOS Coils/.060 plug gaps. 20 in. SRT Reps.
Reply With Quote
Sponsored Links
Advertisement
 
  #4  
Old 01-22-2016, 10:17 PM
Member
My Jeep: 2006 3.7L WK
 
Join Date: Mar 2015
Location: Cincinnati, OH
Posts: 14
Thanks: 1
Thanked 0 Times in 0 Posts
Rep Power: 823
twolfcorner2009 is on a distinguished road
Re: Trouble Diagnosing Cause of P0128 Code

The cooling fan isn't engaged (at least not when I've been able to see it) before I get in drive. I can't tell whether it is or not while I'm driving.

The PCM trips the P0128 Code, which is what prompted me to change the thermostat in the first place. I had the second replacement thermostat put in at the shop when I had to take the jeep in to have my tires rotated and replace the spare tire. I can't imagine the Thermostat is in the wrong way? I'll check when it warms up above freezing (no garage), besides pulling off the hose and all that crap, is there a more simple way to check if my thermostat is stuck open or installed upside down?
Reply With Quote
  #5  
Old 01-23-2016, 12:48 PM
Senior Member
My Jeep: 2006 5.7L WK
 
Join Date: Dec 2009
Location: Home of the Mountain Blue Bird
Posts: 1,340
Thanks: 0
Thanked 73 Times in 61 Posts
Rep Power: 156251
jeepgcoman has a reputation beyond reputejeepgcoman has a reputation beyond reputejeepgcoman has a reputation beyond reputejeepgcoman has a reputation beyond reputejeepgcoman has a reputation beyond reputejeepgcoman has a reputation beyond reputejeepgcoman has a reputation beyond reputejeepgcoman has a reputation beyond reputejeepgcoman has a reputation beyond reputejeepgcoman has a reputation beyond reputejeepgcoman has a reputation beyond repute
Re: Trouble Diagnosing Cause of P0128 Code

Quote:
Originally Posted by twolfcorner2009 View Post
The cooling fan isn't engaged (at least not when I've been able to see it) before I get in drive. I can't tell whether it is or not while I'm driving.

The PCM trips the P0128 Code, which is what prompted me to change the thermostat in the first place. I had the second replacement thermostat put in at the shop when I had to take the jeep in to have my tires rotated and replace the spare tire. I can't imagine the Thermostat is in the wrong way? I'll check when it warms up above freezing (no garage), besides pulling off the hose and all that crap, is there a more simple way to check if my thermostat is stuck open or installed upside down?
If the thermostat was in backwards the engine would overheat, not what is happening to yours. A low coolant level (air in the system) would also cause overheating. Are these new thermostats the correct temperature? What brand are they? If the fan is kicking in too early or engaged all the time, I would think it would be much slower to warm up, but this should cause a MIL to illuminate and a DTC showing it is slow to warm up. I've received that DTC only once, and I run 190* thermostats in both of my vehicles.

At first, when I read your initial issue, I though maybe everything was reading celcius, but that is not possible since you're eventually getting up to 170-180 degrees which is over 300*F. I suppose you could also have a bad temperature gauge too. What you may want to try is to use a candy thermometer in the radiator filler to see what the actual reading is. You'd lose some coolant once it warms up (expansion) with the cap off, but you should be able to get a pretty accurate reading. Another way is to just put your had on the radiator (engine off) once warmed up. If it is uncomfortable to the touch it's probably warming up pretty well. If it's still really cool, you'll easily know the difference. Mine usually gets up to operating temperature in less than 5 miles. Good luck and keep us posted.
__________________
05 LX/RT & 06 WK/GCO, modded similarly, MDS "ON" Light, Vortex Gens, Debadged, DashHawk, BT Catch Can, SRT CAI W/Add Air Inlet, K&N Filter, Sonnax Trans Press Booster, SC Tuner W/Adv Trans Tuning App, DS Tuner, Cust tube headers w/3 in. catback, Bilsteins, SRT frt/rear bumpers, Eibach SRT Lwr Sprgs & Sways, FRI Sidewinder Cam Adv 2*, 6.1 valvetrain, SLP 25% UD Pulley, BBK 90mm TB, SOS Coils/.060 plug gaps. 20 in. SRT Reps.
Reply With Quote
  #6  
Old 01-23-2016, 05:38 PM
mjl2610's Avatar
Senior Member
My Jeep: 2006 4.7L WK
 
Join Date: May 2009
Posts: 1,530
Thanks: 0
Thanked 2 Times in 2 Posts
Rep Power: 4518
mjl2610 has a reputation beyond reputemjl2610 has a reputation beyond reputemjl2610 has a reputation beyond reputemjl2610 has a reputation beyond repute
Re: Trouble Diagnosing Cause of P0128 Code

On a side note, I will be watching this thread and am interested in seeing what the outcome is. The same exact thing is occurring on my fathers 04 intrepid and I cant figure it out. Maybe this thread will give me some ideas
__________________
Reply With Quote
  #7  
Old 01-23-2016, 05:41 PM
Strongjeff's Avatar
Project 8 gauge / ROUSH Protoype Tech

My Jeep: 2008 3.7L WK
 
Join Date: Sep 2012
Location: Woodhaven, MI
Posts: 9,029
Thanks: 420
Thanked 667 Times in 598 Posts
Rep Power: 340219
Strongjeff has a reputation beyond reputeStrongjeff has a reputation beyond reputeStrongjeff has a reputation beyond reputeStrongjeff has a reputation beyond reputeStrongjeff has a reputation beyond reputeStrongjeff has a reputation beyond reputeStrongjeff has a reputation beyond reputeStrongjeff has a reputation beyond reputeStrongjeff has a reputation beyond reputeStrongjeff has a reputation beyond reputeStrongjeff has a reputation beyond repute
Garage
Re: Trouble Diagnosing Cause of P0128 Code

Quote:
Originally Posted by twolfcorner2009 View Post
I'll try to keep this short:

-I'm on my 3rd Thermostat in the last month (Original Thermostat I thought went bad and was stuck open, replaced it with one that didn't solve the Jeep from throwing the code, then put another one in and it hasn't solved the problem).
-I replaced the Coolant Temperature Sensor to see if that was the problem. It apparently wasn't.
-My 06 Grand Cherokee will get up to the first mark on the temp gauge in the dashboard if I start it and just let it idle in the morning after about 10-15 minutes regardless of the outside temp (whether it's the single digits it has been this week or it's 70 degrees like when it's in the summer).
-I drive 20 miles to work on the interstate and by about the end of the first mile, engine temp read out is ~100-115 degrees as read by my scan tool and the needle on the temp gauge is essentially sitting on the post that right on top of the C.
-Now, after running at 70-80mph for 5-10 miles, I usually hit stop and go traffic and my engine will get up to the 180+ degrees after sitting in that for a few minutes.


What in the heck could be going on here? I have a hard time grasping that it's possible to get 2 brand new thermostats that are both bad, back to back. Any insight is appreciated!
could be air in the system, that would usually cause that. there is a breather screw on top of the water neck going to the water pump. id open that up with it running (cold start obviously) and keep it open till coolant comes out. close it and check coolant levels.
__________________
Reply With Quote
  #8  
Old 01-23-2016, 05:44 PM
Strongjeff's Avatar
Project 8 gauge / ROUSH Protoype Tech

My Jeep: 2008 3.7L WK
 
Join Date: Sep 2012
Location: Woodhaven, MI
Posts: 9,029
Thanks: 420
Thanked 667 Times in 598 Posts
Rep Power: 340219
Strongjeff has a reputation beyond reputeStrongjeff has a reputation beyond reputeStrongjeff has a reputation beyond reputeStrongjeff has a reputation beyond reputeStrongjeff has a reputation beyond reputeStrongjeff has a reputation beyond reputeStrongjeff has a reputation beyond reputeStrongjeff has a reputation beyond reputeStrongjeff has a reputation beyond reputeStrongjeff has a reputation beyond reputeStrongjeff has a reputation beyond repute
Garage
Re: Trouble Diagnosing Cause of P0128 Code

Quote:
Originally Posted by jeepgcoman View Post
If the thermostat was in backwards the engine would overheat, not what is happening to yours. A low coolant level (air in the system) would also cause overheating. Are these new thermostats the correct temperature? What brand are they? If the fan is kicking in too early or engaged all the time, I would think it would be much slower to warm up, but this should cause a MIL to illuminate and a DTC showing it is slow to warm up. I've received that DTC only once, and I run 190* thermostats in both of my vehicles.

At first, when I read your initial issue, I though maybe everything was reading celcius, but that is not possible since you're eventually getting up to 170-180 degrees which is over 300*F. I suppose you could also have a bad temperature gauge too. What you may want to try is to use a candy thermometer in the radiator filler to see what the actual reading is. You'd lose some coolant once it warms up (expansion) with the cap off, but you should be able to get a pretty accurate reading. Another way is to just put your had on the radiator (engine off) once warmed up. If it is uncomfortable to the touch it's probably warming up pretty well. If it's still really cool, you'll easily know the difference. Mine usually gets up to operating temperature in less than 5 miles. Good luck and keep us posted.
not advisable to run with cap off, that's not the high point in the 3.7's cooling system. there is a breather screw on top of the water neck going to the water pump. that's the highest point and the one to get al the air out
__________________
Reply With Quote
  #9  
Old 10-03-2016, 08:00 AM
Member
My Jeep: 2006 3.7L WK
 
Join Date: Mar 2015
Location: Cincinnati, OH
Posts: 14
Thanks: 1
Thanked 0 Times in 0 Posts
Rep Power: 823
twolfcorner2009 is on a distinguished road
Re: Trouble Diagnosing Cause of P0128 Code

Update:

I was finally not travelling this past weekend and able to get out and spend some time on the Jeep. I pulled the old thermostat and popped a new one in, refilled the coolant, purged the air, blah blah blah.

It seems to be fixed now. The last thermostat that was put in at the shop must have either A) been the wrong temp thermostat or B) been a dud from the start. Gets up to temp no problem, stays in the 205-215 range for my entire commute. Hard to believe my crap luck, 3 dud thermostats in a row!
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
P0128 code coolant temp low rlefig Trouble Shooting/Problems/Service 54 11-29-2016 06:02 PM
2011 3.6l Dtc p0128 jeepndango Trouble Shooting/Problems/Service 0 12-09-2013 08:41 PM
P0128 Error Code kyle.jg Troubleshooting/Problems Discussion 5 11-07-2012 08:49 PM
Error Code P0128 Daveyc Troubleshooting/Problems 3 08-14-2012 06:54 PM
Diagnosing a Drivetrain Problem? jbefumo Grand Cherokee - ZJ 10 09-16-2010 11:39 AM

» Premium Vendor Showcase
Powered by vBadvanced CMPS v3.2.3

All times are GMT -5. The time now is 08:17 PM.


Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Copyright 2012 - JeepGarage.Org
The Jeep Grand Cherokee Owners Community

JeepGarage.org is in no way associated with or endorsed by FCA US LLC. Chrysler, Dodge, Jeep, Ram, Mopar and SRT are registered trademarks of FCA US LLC.