ECT Temperature Reading Erratic- Help Please!
Tech Contributor
Joined: Jan 2007
Posts: 19,244
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From: Dyer, IN
So I tested this a few more times, each time the voltage changes abruptly and exactly at 120F (or when the voltage at the ECT conntector drops below 1V)
Here is why this is happeing.
From GM's point of view our engines must run in any concievable environmental condition. That means starting in sub zero conditions, or out in the desert.
If GM used one voltage range (the range that appears before 120F OR the range that appears after 120F) it would not be able to accurately determine temperature due to leaving the normmal bounds of a 0-5V sensing system.
I made a curve fit to each seperate "curve" in the graph I posted and crunched the numbers.
If the Lower voltage range were used, ECT temps above 160F would cause the PCM to read a temperature less than 0.
If the higher voltage range were used ECT temps below 60F would give a PCM read of greater that 5V.
Both of these are out of range of the standard 0-5V system, so in order to maintain good resolution and the ability to read very low and high ECT temps 2 ranges were required.
I bet if you test any other voltage at ECT connector it would have similar behavior.
Here is why this is happeing.
From GM's point of view our engines must run in any concievable environmental condition. That means starting in sub zero conditions, or out in the desert.
If GM used one voltage range (the range that appears before 120F OR the range that appears after 120F) it would not be able to accurately determine temperature due to leaving the normmal bounds of a 0-5V sensing system.
I made a curve fit to each seperate "curve" in the graph I posted and crunched the numbers.
If the Lower voltage range were used, ECT temps above 160F would cause the PCM to read a temperature less than 0.
If the higher voltage range were used ECT temps below 60F would give a PCM read of greater that 5V.
Both of these are out of range of the standard 0-5V system, so in order to maintain good resolution and the ability to read very low and high ECT temps 2 ranges were required.
I bet if you test any other voltage at ECT connector it would have similar behavior.
Thread Starter
Racer
Joined: Jun 2010
Posts: 457
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From: LaGrange Ga
Tech Contributor
Joined: Jan 2007
Posts: 19,244
Likes: 1,091
From: Dyer, IN
I take it you are basing your understanding, based off the PCM reading the ECT sensor directly........which it doesn't. All the ECT does, is change the reference to ground. What is actually measured, is a resistor in series with the ECT, that resides in the PCM itself.
Instructor
Joined: May 2011
Posts: 189
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From: St Louis MO
Do you think it's possible that part of the wire could be grounding out somewhere causing a false reading? I would think that if it was, the resistance would be 0 or close to it, causing a higher temperature readout??? This could be an insane hypothesis too though as my electrical knowledge is fairly limited.
Thread Starter
Racer
Joined: Jun 2010
Posts: 457
Likes: 0
From: LaGrange Ga
Update:
Its been nearly 2 months since I added the multimeter to the circuit to monitor what was happening during the failure.
I have sense driven nearly a thousand miles and through the hot start procedure that caused this problem dozens of times without being able to replicate the failure.
At this point I am willing to call this problem fixed.
I think the final solution was the removal and meticulous cleaning of the contacts on the PCM and connector with a cotton swab and alcohol.
Today I am going to pull the test lead and multimeter from the car and continue to monitor. If the problem returns I will fill you guys in.
Thanks for all the help.
Its been nearly 2 months since I added the multimeter to the circuit to monitor what was happening during the failure.
I have sense driven nearly a thousand miles and through the hot start procedure that caused this problem dozens of times without being able to replicate the failure.
At this point I am willing to call this problem fixed.
I think the final solution was the removal and meticulous cleaning of the contacts on the PCM and connector with a cotton swab and alcohol.
Today I am going to pull the test lead and multimeter from the car and continue to monitor. If the problem returns I will fill you guys in.
Thanks for all the help.
