Code PO128
goodoldpapa
11-24-2009, 06:52 PM
Off and on for about the last 4 weeks I've been getting this code. Coolant level is fine. Car temp runs about 170-180 when weather is cool and rainy and perfectly normal when sunny and dry (195-200). Puts out sufficient heat, runs normal, and gets normal gas mileage for what I'm used to (27-28 MPG). I have an 03 SE1 with ~160000 miles. Appreciate your input.
GTP Dad
11-25-2009, 04:24 PM
It is possible that you either have a sticking thermostat or a bad coolant sensor. With this many miles I would replace the thermostat just to be on the safe side in case it is sticking. Cheap insurance against overheating.
3100
11-25-2009, 09:27 PM
I agree with GTP dad, if you think that the wiring is OK for ect sensor, and you don't have time or don't have DVOM to test it then just replace both ect and thermostat and you should be good.
goodoldpapa
01-03-2010, 05:09 PM
I did replace the ECT sensor, hoping that would cure it and also because it's easier to get to. Unfortunately, that didn't keep the code away so I will be replacing the thermostat in the near future. One quick question: Would the fact the temp is not getting to proper level affect other areas of the car's performance?
danielsatur
01-03-2010, 05:28 PM
If the PCU/ECU is getting a long cold Temp signal, the Air/Fuel mix would be rich for a longer
time could cause poor Emissions, fuel economy, and damage catalytic converters.
time could cause poor Emissions, fuel economy, and damage catalytic converters.
3100
01-05-2010, 02:32 PM
If the PCU/ECU is getting a long cold Temp signal, the Air/Fuel mix would be rich for a longer
time could cause poor Emissions, fuel economy, and damage catalytic converters.
I agree with this philosophy, also since thermostat is pita to replace because of the exhaust pipe and shield do this, disconnected upper radiator hose on the radiator side use something to catch coolant tell someone to start the cold engine for 5-6 seconds and if you see coolant flying out t-stat is stuck open and replace it. Also I hope you did not play with cold air intake and repositioning IAT sensor or something of that nature since bad or mispositioned IAT can create the same code.
time could cause poor Emissions, fuel economy, and damage catalytic converters.
I agree with this philosophy, also since thermostat is pita to replace because of the exhaust pipe and shield do this, disconnected upper radiator hose on the radiator side use something to catch coolant tell someone to start the cold engine for 5-6 seconds and if you see coolant flying out t-stat is stuck open and replace it. Also I hope you did not play with cold air intake and repositioning IAT sensor or something of that nature since bad or mispositioned IAT can create the same code.
goodoldpapa
02-14-2010, 05:15 PM
After on again, off again with this code, replaced the thermostat today, let it idle and temp is good. Hopefully this will be the end of this chapter :lol:
Automotive Network, Inc., Copyright ©2026