PCM reading wrong temp?
12-04-2006, 07:03 PM
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PCM reading wrong temp? I recently hooked up Datamaster to log what the car was doing, and see why it was always hot.
After a 10 mile trip to work with varying degrees of traffic, I arrived at work and the gauge was reading 260* and the car was boiling over, but Datamaster was showing the PCM was seeing 182*. This explains why the car is getting hot because the PCM isn't turning the fans on with the temp reading that low.
I have changed out the PCM temp sensor in the water pump, and the fan system is working fine, tried the jump the ALDL trick and the fans kick on, also got an SES light the other day and the fans kicked on with it (vacuum hose perished).
I don't know why the PCM won't see the right temperature, i've tried everything I know, the only thing I can think now is the PCM is bad. Can a PCM go bad yet the car still function normally? (besides the fan/temp problem). Could the wiring be at fault even tho i'm getting a temp reading, all be it, the wrong temp.
Any help would be gratefully appreciated.
BTW, the car is a '94 Firebird Formula LT1 with OBD1.
Thanks
Sara Lou
After a 10 mile trip to work with varying degrees of traffic, I arrived at work and the gauge was reading 260* and the car was boiling over, but Datamaster was showing the PCM was seeing 182*. This explains why the car is getting hot because the PCM isn't turning the fans on with the temp reading that low.
I have changed out the PCM temp sensor in the water pump, and the fan system is working fine, tried the jump the ALDL trick and the fans kick on, also got an SES light the other day and the fans kicked on with it (vacuum hose perished).
I don't know why the PCM won't see the right temperature, i've tried everything I know, the only thing I can think now is the PCM is bad. Can a PCM go bad yet the car still function normally? (besides the fan/temp problem). Could the wiring be at fault even tho i'm getting a temp reading, all be it, the wrong temp.
Any help would be gratefully appreciated.
BTW, the car is a '94 Firebird Formula LT1 with OBD1.
Thanks
Sara Lou
12-04-2006, 08:12 PM
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12-05-2006, 07:44 PM
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As stated in my original post, i've replaced the coolant temp sensor (the one in the water pump with two terminals).
Yes, i've been to shbox a few times, but the only info there is how to test the sensor which i've already changed out.
Sara Lou
Yes, i've been to shbox a few times, but the only info there is how to test the sensor which i've already changed out.
Sara Lou
12-05-2006, 08:16 PM
#5
Could have a ground with high resistance and it's throwing off the ect sensor. Or a wire with high resistance need to read it at the sensor and verify at the pcm connector that you have the same resistance. If it's reading the same it is not a sensor or wiring issue. It could be a pcm but it would be very rare for it to be that far off.
12-06-2006, 07:53 PM
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Thanks for the info/advice 01WS6/tamu, which ground wire would I need to check?. Do I check resistance with the sensor conected or with the wire off?.
Well unless they put the temp gauge sensor in the water pump, i'm pretty sure I changed the right one. 
.
Sara Lou
Originally Posted by autotrix
Are you sure that the sensor you have replaced is indeed your PCM temp sensor and not the temp gauge sender?
.
Originally Posted by Zralou
I recently hooked up Datamaster to log what the car was doing, and see why it was always hot.
After a 10 mile trip to work with varying degrees of traffic, I arrived at work and the gauge was reading 260* and the car was boiling over, but Datamaster was showing the PCM was seeing 182*. This explains why the car is getting hot because the PCM isn't turning the fans on with the temp reading that low.
I have changed out the PCM temp sensor in the water pump , and the fan system is working fine, tried the jump the ALDL trick and the fans kick on, also got an SES light the other day and the fans kicked on with it (vacuum hose perished).
I don't know why the PCM won't see the right temperature, i've tried everything I know, the only thing I can think now is the PCM is bad. Can a PCM go bad yet the car still function normally? (besides the fan/temp problem). Could the wiring be at fault even tho i'm getting a temp reading, all be it, the wrong temp.
Any help would be gratefully appreciated.
BTW, the car is a '94 Firebird Formula LT1 with OBD1.
Thanks
Sara Lou
After a 10 mile trip to work with varying degrees of traffic, I arrived at work and the gauge was reading 260* and the car was boiling over, but Datamaster was showing the PCM was seeing 182*. This explains why the car is getting hot because the PCM isn't turning the fans on with the temp reading that low.
I have changed out the PCM temp sensor in the water pump , and the fan system is working fine, tried the jump the ALDL trick and the fans kick on, also got an SES light the other day and the fans kicked on with it (vacuum hose perished).
I don't know why the PCM won't see the right temperature, i've tried everything I know, the only thing I can think now is the PCM is bad. Can a PCM go bad yet the car still function normally? (besides the fan/temp problem). Could the wiring be at fault even tho i'm getting a temp reading, all be it, the wrong temp.
Any help would be gratefully appreciated.
BTW, the car is a '94 Firebird Formula LT1 with OBD1.
Thanks
Sara Lou
Originally Posted by Zralou
As stated in my original post, i've replaced the coolant temp sensor (the one in the water pump with two terminals).
Yes, i've been to shbox a few times, but the only info there is how to test the sensor which i've already changed out.
Sara Lou
Yes, i've been to shbox a few times, but the only info there is how to test the sensor which i've already changed out.
Sara Lou
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12-10-2006, 06:49 PM
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Well i've checked the wiring, +5v at the yellow wire going to the temp sensor, and 0.77 ohms on the black ground wire (i'd say close enough to "0" allowing for meter error).
I got +5v at the yellow wire using both the black ground wire as the ground source and using the alternator bolt as a ground.
My guestimate now is one of 2 options, the new sensor is bad, or the PCM is.
Now I need to find a connector end that hooks up to the sensor, then I can check the resistance at various temps to see if the sensor is sending the right info to the PCM. Anyone got that part of the wiring loom?.
Sara Lou
I got +5v at the yellow wire using both the black ground wire as the ground source and using the alternator bolt as a ground.
My guestimate now is one of 2 options, the new sensor is bad, or the PCM is.
Now I need to find a connector end that hooks up to the sensor, then I can check the resistance at various temps to see if the sensor is sending the right info to the PCM. Anyone got that part of the wiring loom?.
Sara Lou
