DTC Troubleshooting: P0128
DTC P0128: Cooling System Malfunction
NOTE: Before you troubleshoot, record all freeze data and any on-board snapshot, and review the general troubleshooting information.

DTC Description
Confirmed DTC
Pending DTC
Freeze Frame
P0128 Cooling System Malfunction
     

1.
Radiator fan control command check:

Radiator fan control command check
?1.
Press the engine start/stop button to select the ON mode.

?2.
Clear the DTC with the HDS.


?3.
Turn the blower switch off.

?4.
Check the parameter(s) below with the HDS.
Signal
Threshold
Current conditions
Values
Unit
Values
Unit
FAN HIGH CTRL
OFF
      
FAN LOW CTRL
OFF
      

Do the current condition(s) match the threshold?

     
YES
     
     
     
Go to step 2.
     
NO
     
     
     
Wait until the FAN HIGH CTRL and the FAN LOW CTRL are off, then go to step 4.
2.
Radiator fan operation check:

Radiator fan operation check
?1.
Check the radiator fan operation.

Does the radiator fan keep running?

     
YES
     
     
     
Go to step 3.
     
NO
     
     
     
Wait until the FAN HIGH CTRL and FAN LOW CTRL are off, then go to step 4.
3.
Radiator fan circuit and radiator fan relay check:

Radiator fan circuit and radiator fan relay check
?1.
Check the radiator fan circuit, and the radiator fan relay.

Is it OK?

     
YES
     
     
     
Update the PCM if it does not have the latest software, or substitute a known-good PCM, then do the repair verification.
     
NO
     
     
     
Repair the radiator fan circuit, and the radiator fan relay, then do the repair verification.
4.
Problem verification:

Problem verification
?1.
Let the engine cool until the coolant temperature is 104 °F (40 °C) or less.

?2.
Note the value of ECT SENSOR 1 and ECT SENSOR 2 in the DATA LIST with the HDS.
Signal
Current conditions
Values
Unit
ECT SENSOR 1
    
ECT SENSOR 2
    

?3.
Start the engine, and let it idle.

?4.
Let the engine idle until ECT SENSOR 1 goes up 40 °F (22 °C) or more from the recorded start temperature.
Signal
Current conditions
Values
Unit
ECT SENSOR 1
    

?5.
Check ECT SENSOR 2 in the DATA LIST with the HDS.
Signal
Current conditions
Values
Unit
ECT SENSOR 2
    

?6.
Compare the recorded start value of ECT SENSOR 2 and the present value of ECT SENSOR 2.

Did the temperature rise 13 °F (7 °C) or more?

     
YES
     
     
     
Test the thermostat and replace it if needed, then do the repair verification.
     
NO
     
     
     
Intermittent failure, the system is OK at this time. Check for poor connections or loose terminals at ECT sensor 1, ECT sensor 2, and the PCM.?
Repair verification (OBD STATUS check):

?1.
In order to pass the OBD STATUS check the vehicle must sit with key off for at least 6 hours.

?2.
Press the engine start/stop button to select the ON mode.

?3.
Reset the PCM with the HDS.


?4.
Do the PCM idle learn procedure.

?5.
The coolant temperature must be between 21 °F (-6 °C) and 104 °F (40 °C).

?6.
Test-drive at a steady speed between 15?75 mph (25?120 km/h) for 10 minutes.

?7.
Monitor the OBD STATUS for DTC P0128 in the DTCs MENU with the HDS.
DTC Description
OBD STATUS
P0128 Cooling System Malfunction
 


Does the HDS indicate PASSED, FAILED, or NOT COMPLETED?

     
PASSED
     
     
     
Troubleshooting is complete. If the PCM was substituted, replace the original PCM. If any other Pending or Confirmed DTCs are indicated, go to the indicated DTC's troubleshooting.?
     
FAILED
     
     
     
Go to step 1 and recheck. If the PCM was updated, substitute a known-good PCM, then check the OBD STATUS again.
     
NOT COMPLETED
     
     
     
Meet the test condition, and check the OBD STATUS again.