Well, after changing the thermostat back to 195 degrees, I STILL get the code.

 

Something is wrong for sure. Either, the temp sending unit is bad, the coolant temp sensor is bad or, someone put a high velocity pump on your truck before you got it.

The ECT sensor (coolant temp sensor) is the main sensor that controls that parameter at the PCM level. As the temp goes up, the voltage goes down at the ECT input. This voltage is read at the PCM and if it's not meeting what is set in the PCM, it will trip a DTC.

So, the question is, is the ECT sensor working correctly or, is the circuit for that sensor working or not? Those are the questions you need to find answers for.

How to do that:

First off, what is the reading from your sending unit? More specifically, what does the temp gage on your dash show ~ 200º or not?

IF the temp is good on the dash, we know the sending unit is good. No need to replace it. However, if it is noted that it is NOT reaching temp, then we walk a different path.

Let's start here: <IF> the temp gage shows that is ~195-200 range, then we know that the coolant is reaching that temp and that your sending unit is operational and working.

That leads us down this path: From looking at the schematics, I know that the ECT is the sensor that sends voltage (corresponding to engine temp) back to the PCM.

We know that if the PCM does NOT see the correct voltage, it trips a code.

It is then safe to assume that the root cause may be due to a bad ETC sensor.

However, it may not be a bad sensor. In nine times out of ten, it is, but, there's always a small chance that it's the wiring of the ECT sensor circuit itself.

Let's start walking the path here first. Please report what your dash reading is.

Chris McKenna

 

I'd like to know too, in the first post the OP says it was at 170 using the 180 thermostat. Unless he has an aftermarket gauge or a good scanner, it's hard to know since the factory gauge is not only fairly inaccurate, but it starts at 120 and the next # is 210.(atleast on mine )

And btw, every one I've worked on, the ECT was the one under the alternator. But, just to verify, I always disconnect it and see if the gauge is still working. If it is, then you have the right one.

 

The temp sending unit only has one wire. That is how to identify which is which. You really can't go by the dash gage for accuracy but, you can for gross measurement. In this case, he can simply see if the temp has gone up or not or, if it's working or not at least.

That's what we want to find out- is it working or not and, did the temp increase with the latter T-stat. If his dash indicator shows an increase, we know the temp has indeed risen and that the new T-stat is indeed working.

Now, if there's no increase in temp- even with the latter T-stat- we now look at "how" he installed it along with the temp sending unit to what kind of pump was installed. It is quite possible that the T-stat was not installed properly, the sending unit is bad (if no temp is seen at dash) or, he's running a high volume pump intended for racing or towing. This will throw the temp range out of whack.

Since he mentioned that the prior owner had installed a "new" pump, we have no idea "which type" of pump he / she had installed. So, that is another factor to look at but, only after noting no increase in coolant temp with the new T-stat installed.

If there was a change in temp that is reflected on the dash gage, we then look at the ETC sensor circuit.

All of these T-stats have some kind of tolerance. Some 180 T-stats may spec out at 180º ± 10º which would give a range of 170 to 190. Some may have tighter tolerances / specs so, those may run dead nuts or, ±5º. You never really know with these things as they are never rated either. I have yet to see one T-stat that lists specs as noted above. Plus, when they wear, that spec now drifts out of range or to the point of failure where, the T-stat remains stuck in a closed position thus causing the motor to overheat. I just bought a new 190 for my truck and, it has a fail-safe mechanism built in. When it reaches it's end of life, it remains locked in the open position thus preventing damage from overheating the motor.

 

Well if you need a scaner with a live feed capability, i found one online last night for $50 new, thoguh you pretty much need a laptop, as the software is loaded on your laptop, and plugs in you usb port, then plugs into the obd2 port.

http://www.amazon.com/Crescent-OBD2-...7380870&sr=1-1

I think thatll be my next investment

 

Handheld scan tools are mostly a waste of money. I don't care which ones you look into whether it's auto-x ray, autotap, Actron etc, those are pretty useless as far as data logging, and reading PIDs in real time. Those screens on those things cloud up, or, in the case of x-ray, they are hazy and rainbowed making it nearly impossible to read them. Some report those DOA right out of the box.

I called Autotap and, a few others to talk to someone about which PIDs were supported and, to what extent their data logger is of use. They post back links and never answered my questions.

The best thing is to run software on a laptop with an interface but, not all those packages are the same. Some sell only the hardware interface such as Scantool. Then, if you want to buy the software, it's through a 3rd party and is not supported through the main supplier. Gore research makes some software but, they don't sell the interface so, again, it's off to another supplier for that, and, if the two have compatibility issues, it's fight to get it taken care of.

I like when it's a bundle by one company with great software, support, demo-videos, training is provided, unlimited data logging, and much much more than say, XL scan or Scanmaster. Support is the number one thing that is needed and, to my surprise, most of these so-called "experts" that sell the packages know little to nothing at all about the products they sell.

SO, do some research before you buy or, you may find yourself with nothing but a code reader or useless tool that subs as an expensive paperweight.