I have mods listed in sig and it is tuned for the 160 themostat. About once a month my truck throws the code 128-Coolant thermostat Malfunction. Temp stays around 180ish and truck rund great but what gives? any opionions or previous experience??

 

usually that is a thermostat rplacement code. It basically says that the engine doesnt reach a certain temp in a set amount of time. Might be something your tuner can change for you. It will not hurt anything, but I would ask your tuner about it.

 

stuck thermostat
bad coolant temp sensor
bad iat sensor
had the same code a couple days ago. mines running very rich tho. don't know if its related or not. replaced coolant temp sensor ($15) and didn't fix problems. if your temp guage is reading as usual, its probably not the sensor.

 

I've seen that code on Toyota/Lexus's a few times and usually the thermostat was at fault...as Grumpy5.3 mentioned, the PCM isn't seeing a pre-determined coolant temp within a certain amount of time. May have something to do with the 160 stat, but I've never heard of that happening before. Not 100% sure, but I believe that the PCM references the IAT sensor to determine how quickly the engine should reach temp...if you're t-stat isn't stuck open and the engine is reaching temp as it should, I wonder if the IAT sensor is coated in oil from the CAI and giving a false reading?

 

could be I cleaned my K&N right before I put on the new CAI but it is a dry flow. I'll check it out though ..makes sense...

 

My truck was throwing that code about a month ago and I had found that my tstat was broken and stuck open and my coolant temps werent even barely getting up to even 140 degrees so I put in a new tstat and it fixed it but if you are just running a 160 tstat that shouldnt make it come on.

If I were to guess I would say that you may have a coolant temperature sensor not reading correctly or doing something weird but if you said the gauge is registering fine then that may rule that out.

Do you have any way to do a live scan and see what exactly the temp is reading?

 

no still saving my pennies for hp tuners......

 

the iat sensor is probably getting a bad reading, i'd think it would run a little off tho. iat sensor monitors intake air temps (colder=richer, hotter=leaner). on cold start up the intake air temp and coolant temps should be similar. if the iat sensor is false reading a higher temp, the pcm thinks the coolant should be warmer. clean maf and clear code, see if it returns.

 

cleaned everything and code still pops up. It only does it if I get in and go for a straight drive... no in town. Get in and basicaly set cruise then about 10 minutes later it trips the code. Gotta be in the tune right?

 

i would get that code too.
when the cam was swapped, the tstat was replaced and no code.
i would suggest getting a new tstat.