In this video I will be talking about trouble code P0128 – Coolant Temp Below Thermostat Regulating Temp and going into how your cars thermostat work and how it fails to cause this code to be set.
Also, we will be trying for the first time to open the t-stat with A torch and its pretty cool and surprisingly works. Hope this video helps you understand a little better why this pesky little p0128 code can set sometimes.
T stats on most cars are relatively easy to replace and save you a bunch of money for any DIYer. Too saving money everyone “stay greasy my friends”.
Vehicle Application:
2001 Accord 2.3
Customer Concern: The check engine light is on with a code P0128 for cooling system performance problem.
Average Reported Mileage: 106000
Tests/Procedures: 1. Verify the thermostat is operating correctly, the Engine Control Module (ECM) determines actual engine coolant temperature by the run time of the engine and is watching the Engine Coolant Temperature (ECT) sensor to determine if the engine is warming up fast enough.
2. If the ECT sensor and thermostat is functioning correctly, then follow Honda TSB # 01-064 for a updated ECM for this code.
Tech Tips: If someone starts the vehicle and has the heat on high on a cold day the engine will take longer to warm up and the code may set. I believe the ECM software was revised so it does not expect the engine to warm up as fast.
Tests/Procedures: 1. Let the vehicle get cold and use a scan tool and verify the initial engine coolant temperature is between 20 and 95 degrees F and the initial intake air temperature is also between 20 and 95 degrees F. The difference between initial engine coolant temperature and initial intake air temperature should be a maximum of 3 degrees. Intake air temperature 2 seconds after starting the engine must be nearly equal to initial intake air temperature. Then start the engine and let it idle. Drive the vehicle at a speed between 25 – 55 mph (40 – 88 km/h) for at least 10 minutes.
. If you have difficulty duplicating the DTC, retest after turning off electrical components such as the audio system and A/C,
and try a different gear position.
. Drive the vehicle in this manner only if the traffic regulations and ambient conditions allow.
2. Verify the engine is getting warmed up (above 158 degrees F) in a reasonable amount of time. Given the drive cycle to see if the code resets, look for the engine temperature to reach the estimated engine coolant temperature of about 172 degrees in about 10 minutes of driving.
3. Feel if the lower radiator hose is getting hot indicating the thermostat opened and that there is circulation in the cooling system.
Tech Tips: If the actual engine coolant temperature is below the estimated engine coolant temperature (as estimated by the ECM), a malfunction in the thermostat valve is detected and a DTC P0128 is stored. Malfunction Threshold
. The ECT sensor output is 158ºF (70ºC) or less, and an estimated engine coolant temperature is 172ºF (78ºC) or more.
. The difference between the estimated engine coolant temperature and the ECT sensor output is 27ºF (15ºC) or more.
The TSB for an updated ECM is for 2000-2001 models only.
