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I have been getting a P0128 pretty often lately. It doesn't stay on all the time, sometimes it does go away and comes back. This is the only error code I get when I look up the Check Engine Light.
Based on the error code, I assume its either the Thermostat or the Coolant Temp Switches.
With the car cool, I remove the radiator cap and start the car. The coolant does not flow. I just slow rises after a while. Based on this, I assume the Thermostat is not stuck wide open.
I'm going to test the 2 Coolant Temp Switches. I know the #1 CTS is located at the bottom of the radiator. Can anyone show me a picture of where the #2 CTS is located?
Anyone have an idea what might cause this error code?
Any other troubleshooting ideas?
I have a 2000 RX300 have had it for about 4 years.
The temp gauge has never reached the middle position, it is usually a little below or slightly above the second small white line from the bottom (not counting the bottom thicker white line).
About a month ago I got a P0128 code. I disconnected inspected and reconnected the electrical connector to the coolant temperature sensor. I then cleared the code. About a month later the code reappeared. I cleared it and in has not returned this was a few days ago.
Most cars I have owned the temperature gauge usually is around the middle of the reading, mine has never been for the 4+years I have owned it. Looking through the service history it doesn't look like the thermostat was ever changed.
I guess I have two questions.
1. Do my symptoms sound like a flakey coolant temperature sensor?
2. Where do peoples temp gauge sit when the car is up to temp? I am in the SF bay area where it doesn't get too cold nor too hot.
How is your fuel consumption. You may have a bad thermostat.
Salim
Good question. I bought the car in October of 2013 and the temp gauge behavior has been the same since I got it and never got the P0182 code until a couple of weeks ago. This is why I believe (believed) that my thermostat is fine.
Take a picture of what? The dash gauge? Should I start it cold, first thing in the morning and take a picture of the temp gauge every 1 minute?
The dash gauge has a thick white line and the 9 oclock position and also at the 12 oclock position. The car temp seems to go up really slow and gradual based on the dash gauge.
I have a nice fluke infrared temp meter what are two points (that are easy to access)in the engine area I can compare during startup and warmup?
A coworker also has a RX300 maybe we can start them up and let them idle side by side and see how the responses of the dash gauges compare.
Does anyone know what the specs are for the P0128 code, what temp does it need to see within what time limit?
Basically my dash gauge hovers around the second thin line above the thicker white line that is at the bottom (9 oclock position).
Reason I suggested picture was I no longer have first Gen RX. The word description you gave, is fine but I cant relate to it.
10 mins after driving in summer time should be enough to reach the optimum temperature. Picture of temp gauge at this time is what I was asking for.
From memory, my RX used to show a tad below 1/2 way point (half way point was between 2 white markings ... tad below -> a bit closer towards the C instead of the H side ... estimate ~45% in the range).
Best thing to have would be OBDII scanner with live data. There you can actually get the temp reading from the gauge.
You can also do the layman's test. With the engine cold [morning time], open the radiator cap [confirm the coolant is near the top of the radiator]. Start the engine and see that there is almost no movement in the coolant as you peer through the opening [this confirms that the thermostat is not open]. Remember to put the cap back on.
The other tell tale clue about bad thermostat is no good heat in the cabin when you turn up the cabin air temp.
Salim
ps : All this is a side discussion on thermostat and not your error code.
I do have a ODB scanner that will give me the temp readings what should they be?? Its the type that will connect to my iphone or ipad via wifi.
I took some pictures on the way to work this morning, the car was pared outside and the outside temperature was 57 F
I renamed the photos with minute numbers. Minutes 1-4 were stop and go city driving and minutes 14-26 were freeway driving and minutes 25-37 were stop and go city driving getting to my office.
Last edited by murphysf; May 30, 2018 at 12:06 PM.
Hard to say. The gauges aren't perfect. The scan tool data would be better.
I don't know what exact normal operating temperature is. I drove my car around the block a few times and it reached 180F in the six minutes or so.
The gauge visually corresponded to around your 10 or 12 minute mark, i.e. around that second line.
Hard to say. The gauges aren't perfect. The scan tool data would be better.
I don't know what exact normal operating temperature is. I drove my car around the block a few times and it reached 180F in the six minutes or so.
The gauge visually corresponded to around your 10 or 12 minute mark, i.e. around that second line.
Heere is the scan tool data for yesterdays morning drive
Your data supports my hypothesis. The temp is being controlled by air flow through the radiator and not by the thermostat. It is not a major problem but a small leak acting as bypass.
Please confirm but going by memory the thermostat should be open at 185 ... should regulate the engine temp at 185.
It seems your temp gauge sensor and display are OK.
I still dont know if that issue is causing the CEL.
yes I never believed this issue with my P0182 was the thermostat I think it is the coolant sensor that connects to the engine control module. This is not the same sensor that connects to the dash gauge.
I understand that these sensors can get flakey and I think if the problem keeps coming back I will change the sensor before the thermostat.
The engine temp the OBDII is reading is the output from the temp-sensor. It does not seem to be changing erratically. I suggest a better understanding of the code, and look at things in the loop the test is designed to monitor. Unfortunately I do not have in depth understanding of the error code, but likely hood of the sensor going bad is low imho [based on the data]. If nothing else pans out, sure go ahead and try replacing the sensor [out of desperation imho again].
P0128 Error Code
