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Joe, Technician
Category: Car
Satisfied Customers: 722
Experience:  27 years import and domestic auto repair.
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2004 Hyundai San Fe. 3.5L engine.Emission codes will not

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2004 Hyundai San Fe. 3.5L engine.
Emission codes will not change stays at 4 out of 7.
Have change computers (2) times.
Have driven car with scanner for 70 mile and it stays at
4 our of 7.

Hello and thank you for using just answer! My name is XXXXX XXXXX I will try and help you with this problem. I do see this occasionally..

Just need a little information first. If I understand you correctly, you are trying to ready the monitors in the vehicle as to pass state inspection? Do you know which 3 monitors wont ready? Also, have you replaced the thermostat or coolant sensor in this vehicle?

Customer: replied 3 years ago.

2.7L engine, yes on monitors need 5 6 7 Have not replaced thermostat

or coolant sensor will do now. Will let you know.


Ok good. For most monitors to be ready, the engine needs to be at operating temperature. Sometimes if the thermostat and or coolant sensor are marginal, the engine won't stay at operating temperature consistently, and wont set any trouble codes as a warning. I have found that replacing both of these parts and then continuing with the drive cycle usually does the trick. Let me know how it works out..
Customer: replied 3 years ago.

replaced the thermostat or coolant sensor.

Drove 25 miles still the same.


Ok, a hyundai's drive cycle is a bit longer then most vehicles. You may have to drive it upwards of 100 miles or more. Try to do mostly highway driving, and make sure the air conditioner AND defroster are both OFF.
Oh and make sure there is AT LEAST 1/4 tank of gas in the car.
Joe, Technician
Category: Car
Satisfied Customers: 722
Experience: 27 years import and domestic auto repair.
Joe and 3 other Car Specialists are ready to help you
Customer: replied 2 years ago.

I have been driving for 400 mile it did change form 4 out of 7 now it's at

5 out of 7 for 200 miles stall has hot change must have 6 out of 7 to pass


Ok well at least were making progress...My only suggestion is to be patient and keep driving it. One more monitor and you'll be good to go, Hyundais do take ALOT of driving before the monitors will ready.
Customer: replied 2 years ago.

Back one more time.


Ck engine light come on code P0128

we did replaced the thermostat and coolant sensor.

now what

Ive been doing a lot of research on this, and I can find nothing. Sometimes there is a TSB issued to reprogram the computer, but not in this case. Replacing the thermostat and sensor always repairs the issue. Check the harness/plug at the coolant sensor as this can sometimes be an issue. Here is the code description right out of the Hyundai service manual.



P0128 Hyundai Engine Coolant Temperature Below Thermostat Regulating Temperature
Possible causes - Leaking or stuck open thermostat
- Low engine coolant level
- Insufficient warm up time
- Faulty engine coolant temperature sensor
- Engine coolant temperature sensor harness is open or shorted
- Engine coolant temperature sensor circuit poor electrical connection Tech description If cooling system is not leaking and the fluid level is OK, replacing the thermostat usually takes care of the problem. What about the obd code? If the Powertrain Control Module (PCM) detects the calibrated amount of air flow and engine run time have been met, and the Engine Coolant Temperature (ECT) has not met the minimum thermostat regulating temperature, the code P0128 Hyundai will set. Symptoms- Engine Light ON (or Service Engine Soon Warning Light) P0128 Hyundai Description

An Engine Coolant Temperature (ECT) sensor monitors the temperature of the coolant. This input is used by the Powertrain Control Module (PCM) for engine control and as an enabling criteria for some diagnosis.

The air flow coming into the engine is accumulated and used to determine if the vehicle has been driven within the conditions that would allow the engine coolant to heat up normally to the thermostat regulating temperature. If the coolant temperature does not increase normally or does not reach the regulating temperature of the thermostat, the diagnostic that use ECT as enabling criteria may not run when expected.

I will opt out, hopefully another expert will have a solution for you. Thank you and good luck.

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