So today after work got into my Dart 2.0L and the CEL came on. I was right next to an auto zone so I figured maybe they can bring up the code for me. Well nothing came up for them. So I said thanks anyway and went to the muffler shop that got my muffler delete done. The owner came up plugged in his reader and sure enough Code P0128 came up. He told me what it was and I should see what my dealership had to say about it. I got there and they asked if I was still covered under warranty. Sadly not, I just hit the 40,000 mile mark and my basic ended at 36,000 (funny how this happens right when it ends lol). So the technician says we are a little busy today and it would have to be dropped off tomorrow for a day to find the solution, but he thinks the thermostat is bad and needs to be replaced. So I asked him how much is the estimate to do this? "$450-$550". Yeah no thanks. To be honest I didn't feel any difference in the way the car was operating, since I did this right when I got off work I actually went back home. I actually live 65 miles away from work so I commute that daily with the CEL still on. Now could it be that my coolant level is just low? I let my Dart rest while I've been home and checked the level it was a tad below minimum. Does the CEL go off if its a smidge under? If it's a bad thermostat how much are they really and is it easy to replace at home? Thanks for reading guys hopefully you experienced owners can help me on this.
NerdyDriver
Joined
·
9,250 Posts
Get the correct coolant and bring the coolant level to where it should be. If that does not correct things, replace the thermostat. Post again if you need instructions to replace the thermostat.
50/50 PREDILUTED ANTIFREEZE/COOLANT
10-YEAR/150,000-MILE
Do not add water. Ethylene glycol based
formulation to prevent freeze-up and boilover
while inhibiting corrosion. Must not be
mixed with any non-conforming antifreeze.
OAT (Organic Acid Technology). Developed
for new vehicle technologies.
1 Gallon Bottle
Part No. 68163849AB
MS-12106
CONCENTRATE ANTIFREEZE/COOLANT
10-YEAR/150,000-MILE
Ethylene glycol based formulation to prevent
freeze-up and boil-over while inhibiting
corrosion. Must not be mixed with any
non-conforming antifreeze. OAT (Organic
Acid Technology). Developed for new
vehicle technologies.
1 Gallon Bottle
Part No. 68163848AB
MS-12106
28 - DTC-Based Diagnostics / MODULE, Powertrain Control (PCM), 2.0L / Diagnosis and Testing
P0128-THERMOSTAT RATIONALITY
When Monitored and Set Conditions
When Monitored: This diagnostic runs when the following conditions are met:
•With the engine running.
•Start up coolant temperature less than 65°C (149°F).
•Ambient temperature between -8°C (17.6°F) and 50°C (122°F).
•Average vehicle speed greater than 16 km/h (10 mph) until coolant temperature reaches 85°C.
•Engine speed does not go above 5400 rpm for more than 32 seconds.
•The pass/fail determination point is reached when the coolant temp model reaches 88°C (190.4°F).
Set Conditions:
•The predicted coolant temperature reaches the target threshold before the actual coolant temperature and the PCM detects that the actual engine coolant temperature is too far below the what is acceptable for a good thermostat.
Default Actions:
•MIL light will illuminate.
Possible Causes
LOW COOLANT LEVEL
COOLING SYSTEM ISSUES
THERMOSTAT OPERATION
50/50 PREDILUTED ANTIFREEZE/COOLANT
10-YEAR/150,000-MILE
Do not add water. Ethylene glycol based
formulation to prevent freeze-up and boilover
while inhibiting corrosion. Must not be
mixed with any non-conforming antifreeze.
OAT (Organic Acid Technology). Developed
for new vehicle technologies.
1 Gallon Bottle
Part No. 68163849AB
MS-12106
CONCENTRATE ANTIFREEZE/COOLANT
10-YEAR/150,000-MILE
Ethylene glycol based formulation to prevent
freeze-up and boil-over while inhibiting
corrosion. Must not be mixed with any
non-conforming antifreeze. OAT (Organic
Acid Technology). Developed for new
vehicle technologies.
1 Gallon Bottle
Part No. 68163848AB
MS-12106
28 - DTC-Based Diagnostics / MODULE, Powertrain Control (PCM), 2.0L / Diagnosis and Testing
P0128-THERMOSTAT RATIONALITY
When Monitored and Set Conditions
When Monitored: This diagnostic runs when the following conditions are met:
•With the engine running.
•Start up coolant temperature less than 65°C (149°F).
•Ambient temperature between -8°C (17.6°F) and 50°C (122°F).
•Average vehicle speed greater than 16 km/h (10 mph) until coolant temperature reaches 85°C.
•Engine speed does not go above 5400 rpm for more than 32 seconds.
•The pass/fail determination point is reached when the coolant temp model reaches 88°C (190.4°F).
Set Conditions:
•The predicted coolant temperature reaches the target threshold before the actual coolant temperature and the PCM detects that the actual engine coolant temperature is too far below the what is acceptable for a good thermostat.
Default Actions:
•MIL light will illuminate.
Possible Causes
LOW COOLANT LEVEL
COOLING SYSTEM ISSUES
THERMOSTAT OPERATION
Joined
·
9,250 Posts
It's not difficult to replace the thermostat. You should be able to do it yourself. You need to remove the battery tray to get to it. You might want to get yourself a UView Airlift or similar tool to refill the cooling system without getting air bubbles. Even with the cost of the tool it should still be less than what the mechanic or dealer wants.
07 - Cooling / Engine / THERMOSTAT / Removal
2.0/2.4L
CAUTION:
Do not loosen radiator draincock with system hot and pressurized. Serious burns from coolant can occur.
CAUTION:
The Thermostat and housing is serviced as an assembly. Do not remove the thermostat from the housing, damage to the thermostat may occur.
1.Disconnect and isolate the negative battery cable. If equipped with an Intelligent Battery Sensor (IBS), disconnect the IBS connector first before disconnecting the negative battery cable.
2.Remove the engine cover.
3.Remove the battery (Refer to 08 - Electrical/Battery System/BATTERY/Removal) .
4.Remove the battery tray assembly (Refer to 08 - Electrical/Battery System/TRAY, Battery/Removal) .
5.Remove the belly pan (Refer to 13 - Frame and Bumpers/Under Body Protection/BELLY PAN/Removal) .
6.Drain the cooling system.
7.Lower vehicle.
8.Remove the brake vacuum pump (Refer to 09 - Engine/Cylinder Head/PUMP, Vacuum/Removal) .
9.Remove the three bolts that attach the PDC to the body.
10.Position the PDC to the side to allow for thermostat housing removal.
11.Remove the intake manifold upper support bracket (1) bolts (3).
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12.Loosen but do not remove the bracket nuts (2).
NOTE: The bracket can not be removed at this time, loosening the nuts allow the necessary movement for the thermostat housing to be removed.
13.Remove the coolant recovery bottle return hose (1).
![]()
14.Disconnect the engine coolant temperature sensor harness connector (2).
15.Disconnect the forward most shift cable from the transmission lever.
16.Disconnect the quick-coupling and remove the heater core supply hose (4) . Pliers, Hose Clamp 10288
17.Using Special Tool 10288, release the clamps at the heater core return (5) and thermostat outlet (7).
18.Remove the heater core return hose (5).
19.Remove the thermostat outlet hose (7).
20.Remove the thermostat housing bolts (3).
21.Remove the thermostat housing (6) from the engine.
09 - Engine, 2.0L DOHC / Cylinder Head / PUMP, Vacuum / Removal
REMOVAL
NOTE: The vacuum fitting can be serviced separately without the removal of the pump assembly.
1.Remove the engine cover (Refer to 09 - Engine/Air Intake System/RESONATOR, Air Cleaner/Removal) .
NOTE: Oil may leak from the vacuum pump drive when the pump is removed. Place a shop towel under the pump to prevent oil leakage onto the engine or transmission assembly.
2.Disconnect the vacuum line at the pump (2) by pressing the fitting retainer (1) while carefully pulling the line from the fitting (4).
![]()
3.Remove the vacuum pump mounting bolts (1) and the vacuum pump (2).
![]()
4.Remove and discard the vacuum pump gasket. Note the location of the pump drive tab.
07 - Cooling / Engine / THERMOSTAT / Removal
2.0/2.4L
CAUTION:
Do not loosen radiator draincock with system hot and pressurized. Serious burns from coolant can occur.
CAUTION:
The Thermostat and housing is serviced as an assembly. Do not remove the thermostat from the housing, damage to the thermostat may occur.
1.Disconnect and isolate the negative battery cable. If equipped with an Intelligent Battery Sensor (IBS), disconnect the IBS connector first before disconnecting the negative battery cable.
2.Remove the engine cover.
3.Remove the battery (Refer to 08 - Electrical/Battery System/BATTERY/Removal) .
4.Remove the battery tray assembly (Refer to 08 - Electrical/Battery System/TRAY, Battery/Removal) .
5.Remove the belly pan (Refer to 13 - Frame and Bumpers/Under Body Protection/BELLY PAN/Removal) .
6.Drain the cooling system.
7.Lower vehicle.
8.Remove the brake vacuum pump (Refer to 09 - Engine/Cylinder Head/PUMP, Vacuum/Removal) .
9.Remove the three bolts that attach the PDC to the body.
10.Position the PDC to the side to allow for thermostat housing removal.
11.Remove the intake manifold upper support bracket (1) bolts (3).
12.Loosen but do not remove the bracket nuts (2).
NOTE: The bracket can not be removed at this time, loosening the nuts allow the necessary movement for the thermostat housing to be removed.
13.Remove the coolant recovery bottle return hose (1).
14.Disconnect the engine coolant temperature sensor harness connector (2).
15.Disconnect the forward most shift cable from the transmission lever.
16.Disconnect the quick-coupling and remove the heater core supply hose (4) . Pliers, Hose Clamp 10288
17.Using Special Tool 10288, release the clamps at the heater core return (5) and thermostat outlet (7).
18.Remove the heater core return hose (5).
19.Remove the thermostat outlet hose (7).
20.Remove the thermostat housing bolts (3).
21.Remove the thermostat housing (6) from the engine.
09 - Engine, 2.0L DOHC / Cylinder Head / PUMP, Vacuum / Removal
REMOVAL
NOTE: The vacuum fitting can be serviced separately without the removal of the pump assembly.
1.Remove the engine cover (Refer to 09 - Engine/Air Intake System/RESONATOR, Air Cleaner/Removal) .
NOTE: Oil may leak from the vacuum pump drive when the pump is removed. Place a shop towel under the pump to prevent oil leakage onto the engine or transmission assembly.
2.Disconnect the vacuum line at the pump (2) by pressing the fitting retainer (1) while carefully pulling the line from the fitting (4).
3.Remove the vacuum pump mounting bolts (1) and the vacuum pump (2).
4.Remove and discard the vacuum pump gasket. Note the location of the pump drive tab.
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