Engine-Codes - Honda - P0128 Honda

P0128 Honda Code - Cooling System Malfunction

- Code Popularity: 96,475 Views
- Repair Importance Level: 3/3
- Repair Difficulty Level: 2/3
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What are the Possible Causes of the DTC P0128 Honda?

NOTE: The causes shown may not be a complete list of all potential problems, and it is possible that there may be other causes.
  • Low engine coolant level
  • Leaking or stuck open thermostat
  • Faulty Engine Coolant Temperature (ECT) Sensor 1
  • Faulty Engine Coolant Temperature Sensor 2
  • Faulty Intake Air Temperature (IAT) Sensor
  • Faulty Manifold Absolute Pressure (MAP) Sensor
  • Faulty Crankshaft Position (CKP) Sensor
  • Faulty Barometric Pressure (BARO) Sensor
  • Faulty Radiator Fan

Code Tech Notes

If the cooling system is not leaking and the fluid level is OK, replacing the thermostat usually takes care of the problem.

When troubleshooting a 2000-2001 Accord or 2001-2002 Civic, if the PGM Tester tells you there is a DTC P0128 (Cooling System Malfunction) or P1486 (Cooling System Malfunction) set, it's really reporting the same thing. DTC P0128 is an SAE or generic Diagnostic Trouble Code (DTC) while P1486 is a manufacturer-specific DTC. Since these DTCs are similar, the PGM Tester sometimes reports a P0128 when it detects a P1486 or vice versa.









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How to Fix the DTC P0128 Honda?

Check the 'Possible Causes' listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector pins.

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What is the Cost to Diagnose the Code?

Labor: 1.0

The cost to diagnose the P0128 Honda code is 1.0 hour of labor. The diagnosis time and labor rates at auto repair shops vary depending on the location, make and model of the vehicle, and even the engine type. Most auto repair shops charge between $75 and $150 per hour.

What are Code Possible Symptoms?

  • Engine Light ON (or Service Engine Soon Warning Light)

What Does the P0128 Honda Code Mean?

The thermostat is closed when the engine coolant temperature is low, and it stops the circulation of engine coolant to speed up engine warm-up. When the engine coolant temperature increases, the thermostat opens and circulates the engine coolant to control its temperature. When the engine coolant temperature decreases, the opening area of the thermostat is reduced to regulate the engine coolant temperature. If the thermostat sticks open, engine warm-up is delayed, and exhaust emissions are adversely affected. The Powertrain Control Module (PCM) measures the rise in the coolant temperature after the engine starts at the engine block and at the radiator, and it estimates the characteristics of the engine coolant temperature by calculations based on those two temperatures and the driving conditions. When the Engine Coolant Temperature (ECT) Sensor 2 immediately increases from the starting value, it is defined as the thermostat stuck open. When ECT Sensor 1 does not reach a specified value at a certain condition, it is defined as a thermostat malfunction.

P0128 Honda Code - Cooling System Malfunction

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