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So I failed smog today because of a recently cleared code, coolant temperature plausibility. I've replaced the thermostat, double temp switch and the coolant temperature sensor. After all that I'm still getting the code. Any help would be appreciated. Thanks.
 

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How long since you last cleared the codes?

Once you clear any codes the car has to go through a number of drive cycles before the system readiness codes are cleared. Usually a few cold starts with driving to a full warm up and some highway driving will get the system readiness to clear. Usually about 10 miles, 3 in city, 7 on highway depending on a number of factors.

Also search and find the hidden OBC menu to access #7 to view the coolant temp. It should hold steady at 78-79C after about 4-6 miles of driving depending on the outside temps. Temps should not drive at highway speeds.

A good clue is the oil temp should never be below the 1st dot after about 8-10 miles depending on the outside temps.

If the oil temp drops below the first dot when driving, I would say your temps may be too low and the thermostat may not be working correctly.

I am stating this based upon my only owning the car with temps no higher than 50F ambients and originally having a bad stat and watching the temp behavior for both the coolant and oil VERY closely over the past month.
 

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Discussion Starter #3
I replaced all the parts and cleared the codes last weekend. Temps have never been an issue. I'm kind of at a loss here.
 

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So how are you determining the temperatures??

What are the values?

By any chance are you getting any catalytic converter codes?

I have a feeling, have not been able to confirm this, if the O2 sensors do not play correctly, warm up right, there may be some correlation to triggering the Coolant Temp Plausibility, when engine temp may not be a problem??
 

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Be careful on the wiring issue, I would bring up the hidden OBC menu and watch the coolant temp.

I have only 1 time had a Coolant Temp code after I had changed the tstat. I actually had the OBC displaying the temp and was watching it the entire time I was driving. I had a stretch of road that was about 50 MPH for about 3-5 miles. I came to a traffic light, stopped for a few minutes, made a left turn when the light changed and on pops the CEL!

Turns out I had temp and cat converter codes, I called BS on this, reset the codes, no problem since. I think that at times under light load the O2 sensors may cool off and start to get lazy and possibly trigger these codes.

My O2 sensors are only about 6 months old and I feels that maybe the light load, long cruise with cooler outside air temps can cause this??
 

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So I failed smog today because of a recently cleared code, coolant temperature plausibility. I've replaced the thermostat, double temp switch and the coolant temperature sensor. After all that I'm still getting the code. Any help would be appreciated. Thanks.
I'm having the same issue. Code 69 keeps coming up even after replacing the 3 parts quoted above. Did you ever resolve this issue (SES light and code 69)? The only other code that pops is 50 Switch Chain Grip.
 

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What about the thermostat? What is the car warming up to and how quickly? This code is really a thermostat failure code (that can be caused by other things like sensors if they happen to fail).
 

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The thermostat was replaced last week in an effort to clear this code. I had replaced the two sensors already, so I though the tstat change would stop the code.
 

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The most common cause of this code recurring with all parts replaced is the plug for the top sender. The solution is to add solder to the pins on the sensor so the plug bites better. IIRC the plug is not available. There are threads try adding nightkrawler or 68fb in the user name. 68FB invented it but nightkrawler started a thread where it was completely discussed including how too.
 

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What is the DME reading in temp and how quick does it get there? It will need to be about 175* F or 79* fairly quickly (and not dip down much) to prevent plausibility.
 

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I got the Temp Plausibility 105 code today as well. Driving on the highway this morning with temps in the low 60F's hidden OBC said I was running between 75º-79ºC which I think is low. I'm hoping that the thermostat and sensors will rid me of this error. Work is scheduled for next Friday.
 

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