1998 Toyota Corolla p0125 can't figure it out!!!

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#1
1998 Toyota Corolla 1.8l
311,423 miles

Ok. I've replaced the coolant temp sensor, replaced the o2 sensors, and the thermostat. What the hell else can it be????

I've been searching for months on how to fix this issue, and now, when the ecm reads from the sensor 207 on the ECT it's three quarters up the Gauge. I don't get it. I don't know what I'm missing. Coolant fans work. Thermostat is a OEM product. I'm replacing the ECT Sensor this weekend with a dealer part, but I'm at my wits end.

Anyone that can help would be greatly appreciated!!!
 

nickb2

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#2
Is this a 3.0l or a 2.2l?

Diagnostic is different for both engines.

I will assume it is a 2.2.

So read this pdf, it may help you to get it.

Also tell me if it is a california emission car/

If all checks out ok, it can only be the ECM.
 

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nickb2

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#5
So after more investigation, no TSB's of note for the P0125 code.

So if all wiring checks out, o2s are new, and a new ect installed OEM, then an ECM is in order maybe.

Here is a PDF of entire powertrain control schematics.
 

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billr

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#8
Look at ECT in live-data, to see what the PCM is actually reading. The obvious suspect now is the wiring from ECT sensor to PCM (including connectors). If that system is like most others (a negative temp-coefficient thermistor), a poor connection in the wiring results in a too-low temp reading.
 
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#9
Look at ECT in live-data, to see what the PCM is actually reading. The obvious suspect now is the wiring from ECT sensor to PCM (including connectors). If that system is like most others (a negative temp-coefficient thermistor), a poor connection in the wiring results in a too-low temp reading.

Live data is indicating 33.7% load
ECT 200*f
Short term fuel trim is 19.5
Long term fuel trim is 19.5
MAP is 10.0
Engine rpm is 645
Ignition advance stays between 5-13
O2 sensor 1 is 0.020 volts
02 sensor 2 is 0.000 volts.
That downstream sensor is brand new, third one I've put in and I have power coming from the pigtail.
 

billr

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#10
200F looks fine, of course, so a few more questions:

Does ECT drop down to ambient when the car has sat long enough to cool down to ambient? Do the ECT and IAT/MAT read about the same as each other then?

When the data above was take, was the engine idling? If an auto trans, in P/N or in some driving gear?

What are the units for the MAP value?

Are the O2 readings "stuck" at zero, or do they move at all?

And, the best for last... how long does it take ECT to rise from a cold ambient to 200F? And what is your "cold ambient"?
 
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#11
Agree with billr ...
Don't concentrate on the ECT look at what are o2 readings.
Have we tracked the o2 sensor voltage- (exceed .045 ...?) the info is in in first PDF my colleague nickb2 added - All I see is you replaced the sensors .
I also think I see the Fuel trims as high - @+20 at idle *- could this be a sign of weak fuel pressure? Not able to go rich?

* I will reread details again time permitting
 
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billr

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#12
Kev, is that a typo? Did you mean .450V for the O2, not .045?

I do want the ECT looked at still, to be sure it isn't "stuck" at 200F. Also, some definitions I find for that code (P0125) are that the engine is too slow to get up to temp, not just that it won't get up to temp.
 
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#13
typo - should be .450
I referenced the troube tree nickb2 posted for details .