Need help with resistance !, CEL GONE !!! Options

[Culpable04]

I'm gonna be replacing the EGR gas temp. sensor with a resistor, so I can clear a CEL I have, but in order to replace it with the right resistor I need to know the resistance on such sensor at normal engine operating temperatures.

the resistance changes with the temperature, if anybody know what should be the resistance at normal operating temperature or is willing to test the sensor for me, it's be a great help.


BTW. I can't test mine because the engine I have on my celi doesn't have the port for the probe to get teh temperature reading. that's how I got the CEL.

This post has been edited by Culpable04: Jun 15, 2007 - 12:45 PM

[bindertch]

At 122F it should be 64-97 ohms, at 212F it should be 11-16 ohms, at 302F it should be 2-4 ohms. That sensor tells the ECM how hot the exhaust gas is after it goes through the EGR cooler. Depending on how hot it is (just like cooler air) is how much fuel gets injected.

[Gary]

On 5th gen EGR system, non-California cars come with short pins at the EGR temp sensor.
That mean when removing the EGR stuff, there is no error code.
It should be the same on 6th gen.
No resistor needed.

This post has been edited by Gary: Jun 14, 2007 - 8:55 AM

[Culpable04]

On 5th gen EGR system, non-California cars come with short pins at the EGR temp sensor.
That mean when removing the EGR stuff, there is no error code.
It should be the same on 6th gen.
No resistor needed.

what do you mean by short pins ? can you elaborate a little bit.

my EGR system is still in place but since the engine doesn't have the hole on the back of the cylinder for the temperature probe I'm having a CEL, I though about putting a resistor in place to fix it, but if what you suggest works I'd go with that.

[Gary]

There are 2 wires going to the EGR temp sensor.
Disconnect the connector from the temp sensor.
Then, "short" them (connect 2 wires together)
Or you can ground the THG wire at the ECU.

[Culpable04]

There are 2 wires going to the EGR temp sensor.
Disconnect the connector from the temp sensor.
Then, "short" them (connect 2 wires together)
Or you can ground the THG wire at the ECU.

will try that today after work, and I'll post results tomorrow.

[cheeco]

the temp probe is there to tell the ecm if/when the egr is operating properly. when the egr activates the probe temperature will go up, when the egr is not activated the probe temperature will go down. you really cant fool it with a resistor. im not sure if an obd1 ecm will check if the probe temp is wrong at a certain time, but an obd2 ecm definately will. if you have the probe connected properly, ie no short or open, but it is just hanging out in the engine bay, id be willing to bet it is monitored and will set the MIL if it doesnt see the correct resistance/temp at the right time.

[Culpable04]

the temp probe is there to tell the ecm if/when the egr is operating properly. when the egr activates the probe temperature will go up, when the egr is not activated the probe temperature will go down. you really cant fool it with a resistor. im not sure if an obd1 ecm will check if the probe temp is wrong at a certain time, but an obd2 ecm definately will. if you have the probe connected properly, ie no short or open, but it is just hanging out in the engine bay, id be willing to bet it is monitored and will set the MIL if it doesnt see the correct resistance/temp at the right time.

yeah, that makes sense

I have everything needed but my engine is from a corolla so it doesn't have the port for the probe to check the temp. so I'll have to live with the light on and the low MPG until I can source another 7AFE from a 94-95 for cheap

[Gary]

the temp probe is there to tell the ecm if/when the egr is operating properly. when the egr activates the probe temperature will go up, when the egr is not activated the probe temperature will go down. you really cant fool it with a resistor. im not sure if an obd1 ecm will check if the probe temp is wrong at a certain time, but an obd2 ecm definately will. if you have the probe connected properly, ie no short or open, but it is just hanging out in the engine bay, id be willing to bet it is monitored and will set the MIL if it doesnt see the correct resistance/temp at the right time.

Nope, not on OBD I.
As I already posted above, if you can ground the THG or short the pins on the EGR temp sensor, you will not have errror code.
The diagram below is straight from the BGB.

[Batman722]

but Gary there is problem, his ECU is from a cali spec celica, all STs are cali spec IIRC. His ECU will always be looking for the EGR signal...

[Gary]

Dustin,
The method above is how most CA-spec alltrac owner get rid of their EGR error code when removing the EGR or when putting a JDM engine in (while retaining the stock CA-spec ECU.) It works for 4AFE and I don't see why it shouldn't work on 7AFE OBD-I. Try it and see. It doesn't hurt anything.

[cheeco]

The diagram below is straight from the BGB.

but from what year, i just looked up the 95 celica 7AFE engine control BGB wiring diagram at celicatech and there is no short pin shown. the ecm may be different, shorting a circuit grounded or controled by the ecm could cause damage to it...

http://www.celicatech.com/imagearchive/bgb...ewd/circuit.htm pg 92

[Gary]

The diagram below is straight from the BGB.

but from what year, i just looked up the 95 celica 7AFE engine control BGB wiring diagram at celicatech and there is no short pin shown. the ecm may be different, shorting a circuit grounded or controled by the ecm could cause damage to it...

http://www.celicatech.com/imagearchive/bgb...ewd/circuit.htm pg 92

That is because all ST's are CA spec like Dustin mentioned above.
See the second post, the resistance of the temp sensor is exponentially approaching zero when the temp. goes up.
And normal exhaust temp is much higher than that.
But if you don't feel comfortable with this, don't do it.

[Culpable04]

guys, it has been a lot of help for me, all your info has help me.

I got rid of the CEL last night by shorting the 2 wires going to the EGR temp sensor. so Gary was right, but I appreciate the input from everyone, this was a nice discussion that lead to an answer.

Thanks a bunch

[Gary]

Glad it works out for you.