PCM reading wrong temp?

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Dec 4, 2006 | 07:03 PM

Zralou

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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

Dec 4, 2006 | 08:12 PM

2001NBMZ28

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Don't know for sure - have you visited shoebox's site? http://shbox.com/1/4th_gen_tech2.html#ect

Dec 5, 2006 | 01:21 PM

01WS6/tamu

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Sounds like the coolant temperature sensor is bad. THe gauge and ct sensor share two separate sending units.

Dec 5, 2006 | 07:44 PM

Zralou

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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

Dec 5, 2006 | 08:16 PM

01WS6/tamu

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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.

Dec 5, 2006 | 10:00 PM

autotrix

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Are you sure that the sensor you have replaced is indeed your PCM temp sensor and not the temp gauge sender?

Dec 6, 2006 | 07:53 PM

Zralou

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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?.

Quote:

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?

Well unless they put the temp gauge sensor in the water pump, i'm pretty sure I changed the right one.

Quote:

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

Quote:

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

Sara Lou