ECT switch resistance
Lead Driver
Joined: Sep 2006
Posts: 7,907
Likes: 143
From my hand written notes.
194 degrees..............275,000 ohms.
203.........................2,300 ohms.
212.........................2,000 ohms.
230.........................1,500 ohms.
As you can see the temp vs resistance change is quite steep between 194 and 203.
This is the signal the PCM uses.
This is the normal running temp range for the motor.
Allow for some tolerence and your meter accuracy of at least 10%.
Good luck.
194 degrees..............275,000 ohms.
203.........................2,300 ohms.
212.........................2,000 ohms.
230.........................1,500 ohms.
As you can see the temp vs resistance change is quite steep between 194 and 203.
This is the signal the PCM uses.
This is the normal running temp range for the motor.
Allow for some tolerence and your meter accuracy of at least 10%.
Good luck.
Thread Starter
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New User
Joined: Oct 2010
Posts: 11
Likes: 0
From: Ontario
ETC resistance
Thanks for the info regarding ETC at operating temp but can you tell me what the resistance is when outside temperature is 32F (cold engine not running).
Also I have no fast idle on cold start, could the ETC cause this problem.
Also I have no fast idle on cold start, could the ETC cause this problem.
Lead Driver
Joined: Sep 2006
Posts: 7,907
Likes: 143
Here is the general cold start.
When the key is operated to RUN before cranking it powers up the PCM, the PCM looks at the ECT resistance and the Intake Air Temp sensor values.
This is how the PCM knows it will be a total cold start.
The values set fuel injection level from fixed tables, ignition timing is advanced and the IAC is opened for high idle and extra air for the rich fuel.
Check out the IAC first for being stuck closed when it cools from a hot shutdown.
If you can get the engine to run by holding the throttle open a bit, it's a sure sign the IAC is not open.
If after warm up it idles ok that is a sign as well iT has begun to work.
During the first approx minute the OX sensors are still too cold to operate until they get up to at least 600 degrees in temp. The heaters in them help speed up the heating.
Check for codes that may tell something.
Good luck.
When the key is operated to RUN before cranking it powers up the PCM, the PCM looks at the ECT resistance and the Intake Air Temp sensor values.
This is how the PCM knows it will be a total cold start.
The values set fuel injection level from fixed tables, ignition timing is advanced and the IAC is opened for high idle and extra air for the rich fuel.
Check out the IAC first for being stuck closed when it cools from a hot shutdown.
If you can get the engine to run by holding the throttle open a bit, it's a sure sign the IAC is not open.
If after warm up it idles ok that is a sign as well iT has begun to work.
During the first approx minute the OX sensors are still too cold to operate until they get up to at least 600 degrees in temp. The heaters in them help speed up the heating.
Check for codes that may tell something.
Good luck.
Thread Starter
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New User
Joined: Oct 2010
Posts: 11
Likes: 0
From: Ontario
cold ETC resistance
Thanks for the heads up, I will try that. I still need the 32F cold resistance as checked across the ETC. if you know that, would be appreciated as the ETC might have something to do with the cold start, low idle problem.
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Lead Driver
Joined: Sep 2006
Posts: 7,907
Likes: 143
I don't have the whole temp range to offer.
I would say however that a faulty ECT often acts like a cold start value that has resistance high or an open.
Usually this would not cause the IAC to close down for low idle but mimic a cold start that does not change.
It would tend to have an effect on fuel mileage from excess richness it's signal would send to the PCM.
Often the OX sensors would detect the excess richness and try to shift the fuel tables all the way to their lean end and set 2 codes to reflect that situation.
Another way to look at it is the ECT, IAT sensors are the data inputs to the computer.
The computer logics for a decision on fuel, ignition timing and IAC opening as output responses.
So the ECT is part of the input data. There are a number of decisions made before the IAC is sent a signal to open.
I would still clean the IAC and the throttle plate with spray cleaner.
Take the IAC off to clean and make sure the pintle moves freely inside.
Good luck.
I would say however that a faulty ECT often acts like a cold start value that has resistance high or an open.
Usually this would not cause the IAC to close down for low idle but mimic a cold start that does not change.
It would tend to have an effect on fuel mileage from excess richness it's signal would send to the PCM.
Often the OX sensors would detect the excess richness and try to shift the fuel tables all the way to their lean end and set 2 codes to reflect that situation.
Another way to look at it is the ECT, IAT sensors are the data inputs to the computer.
The computer logics for a decision on fuel, ignition timing and IAC opening as output responses.
So the ECT is part of the input data. There are a number of decisions made before the IAC is sent a signal to open.
I would still clean the IAC and the throttle plate with spray cleaner.
Take the IAC off to clean and make sure the pintle moves freely inside.
Good luck.
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Thread Starter
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New User
Joined: Oct 2010
Posts: 11
Likes: 0
From: Ontario
I don't have the whole temp range to offer.
I would say however that a faulty ECT often acts like a cold start value that has resistance high or an open.
Usually this would not cause the IAC to close down for low idle but mimic a cold start that does not change.
It would tend to have an effect on fuel mileage from excess richness it's signal would send to the PCM.
Often the OX sensors would detect the excess richness and try to shift the fuel tables all the way to their lean end and set 2 codes to reflect that situation.
Another way to look at it is the ECT, IAT sensors are the data inputs to the computer.
The computer logics for a decision on fuel, ignition timing and IAC opening as output responses.
So the ECT is part of the input data. There are a number of decisions made before the IAC is sent a signal to open.
I would still clean the IAC and the throttle plate with spray cleaner.
Take the IAC off to clean and make sure the pintle moves freely inside.
Good luck.
I would say however that a faulty ECT often acts like a cold start value that has resistance high or an open.
Usually this would not cause the IAC to close down for low idle but mimic a cold start that does not change.
It would tend to have an effect on fuel mileage from excess richness it's signal would send to the PCM.
Often the OX sensors would detect the excess richness and try to shift the fuel tables all the way to their lean end and set 2 codes to reflect that situation.
Another way to look at it is the ECT, IAT sensors are the data inputs to the computer.
The computer logics for a decision on fuel, ignition timing and IAC opening as output responses.
So the ECT is part of the input data. There are a number of decisions made before the IAC is sent a signal to open.
I would still clean the IAC and the throttle plate with spray cleaner.
Take the IAC off to clean and make sure the pintle moves freely inside.
Good luck.
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