DTC Troubleshooting: P0128
DTC P0128: Cooling System Malfunction
NOTE: Before you troubleshoot, review the general troubleshooting information.

DTC Description
Confirmed DTC
Pending DTC
P0128 Cooling System Malfunction
   

1.
Radiator fan control command check:

Radiator fan control command check
?1.
Turn the vehicle to 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 2.
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
     
     
     
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
     
     
     
Check for any authorized service information related to the DTCs or symptoms you are troubleshooting, or substitute a known-good PCM, then recheck. If DTC P0128 goes away and the PCM was substituted, replace the original PCM.?
     
NO
     
     
     
Repair the radiator fan circuit, and the radiator fan relay.?
4.
Problem verification:

Problem verification
?1.
Turn the vehicle to the OFF (LOCK) mode.

?2.
Let the engine cool until the coolant temperature is 104 °F (40 °C) or less.

?3.
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
    

?4.
Start the engine, and let it idle.

?5.
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
    

?6.
Check ECT SENSOR 2 in the DATA LIST with the HDS.
Signal
Current conditions
Values
Unit
ECT SENSOR 2
    

?7.
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.?
     
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. If the on-board snapshot of this DTC is recorded, try to reproduce the failure under the same conditions with the on-board snapshot.?