P0128
DTC P0128: Cooling System MalfunctionNOTE: If the DTCs listed below are stored at the same time as DTC P0128, troubleshoot those DTCs first, then recheck for P0128.
P0112, P0113: Intake air temperature (IAT) sensor
P0116, P0117, P0118, P0125: Engine coolant temperature (ECT) sensor
P0300: Random misfire
P0301, P0302, P0303, P0304: No.1, No.2, No.3, or No.4 cylinder misfire
P0335, P0339: Crankshaft position (CKP) sensor
P2227, P2228, P2229: Barometric pressure (BARO) sensor
P2646, P2647, P2648, P2648: VTEC system
P0506, P0507: Idle control system malfunction
P0511: Idle air control (IAC) valve
DTC P0128 can occasionally set when the hood is opened while the engine is running.
1. Turn the ignition switch ON (II).
2. Do the DTC CLEAR in the CLEAR MENU with the Honda PGM Tester or the HDS.
3. Turn the blower switch OFF.
4. Turn the A/C switch OFF.
5. Check the FAN CTRL in the DATA LIST with the Honda PGM Tester or the HDS.
Is it OFF?
YES - Go to step 6.
NO - Wait until the FAN CTRL is turned off, then go to step 6.
6. Check the ECT SENSOR in the DATA LIST with the Honda PGM Tester or the HDS, then check the radiator fan operation
Does a radiator fan keep running when the engine coolant temperature less than 158 °F (70 °C)?
YES - Check the radiator fan circuit, the radiator fan switch circuit, and the radiator fan switch. If the circuits and the switch are OK, go to step 21.
NO - Go to step 7.
7. Start the engine. Hold the engine speed at 3,000 rpm with no load (in Park or neutral) until the radiator fan comes on, then let it idle.
8. Turn the ignition switch OFF.
9. Turn the ignition switch ON (II).
10. Do the RADIATOR FAN TEST in the INSPECTION MENU with the Honda PGM Tester or the HDS for 20 minutes.
11. Check the ECT SENSOR in the DATA LIST with the Honda PGM Tester or the HDS.
Is about 140 °F (60 °C) or less, or 1.25 V or more indicated?
YES - Intermittent failure, system is OK at this time.
NO - Go to step 12.
12. Turn the ignition switch OFF.
13. Cool down the engine until the coolant temperature is between 23 °F (-5 °C) and 95 °F (35 °C).
14. Replace the thermostat.
15. Turn the ignition switch ON (II).
16. Do the ECM/PCM RESET in the CLEAR MENU with the Honda PGM Tester or the HDS.
17. Do the ECM/PCM idle learn procedure.
18. Start the engine. Hold the engine speed at 3,000 rpm with no load (in Park or neutral) until the radiator fan comes on, then let it idle.
19. Check for Temporary DTCs or DTCs in the DTCs MENU with the Honda PGM Tester or the HDS.
Are any Temporary DTCs or DTCs indicated?
YES - If DTC P0128 is indicated, check the cooling system, then go to step 1. If any other Temporary DTCs or DTCs are indicated, go to the indicated DTCs troubleshooting.
NO - Go to step 20.
20. Monitor the OBD STATUS for DTC P0128 in the DTCs MENU with the Honda PGM Tester or the HDS.
Does the screen indicate PASSED?
YES - Troubleshooting is complete.
NO - If the screen indicates FAILED, check for cooling system, then go to step 1. If the screen indicates NOT COMPLETED, go to step 18 and recheck.
21. Update the ECM/PCM if it does not have the latest software, or substitute a known-good ECM/PCM.
22. Cool down the engine until the coolant temperature is between 23 °F (-5 °C) and 95 °F (35 °C).
23. Start the engine. Hold the engine speed at 3,000 rpm with no load (in Park or neutral) until the radiator fan comes on, then let it idle.
24. Check for Temporary DTCs or DTCs in the DTCs MENU with the Honda PGM Tester or the HDS.
Are any Temporary DTCs or DTCs indicated?
YES - If DTC P0128 is indicated, check for poor connections or loose terminals at the ECT sensor and the ECM/PCM, then go to step 1. If any other Temporary DTCs or DTCs are indicated, go to the indicated DTC troubleshooting.
NO - If the ECM/PCM was updated, troubleshooting is complete. If the ECM/PCM was substituted, replace the original ECM/PCM.