I just checked the reference voltage going into my Coolant Temp Sensor, and it was only 4.1, and is supposed to be 5.0. I got a code 15 (low cts voltage) a few days ago. Cars runs very rich, stalls out. Replacing the cts won't help if I still only get 4.1 ref volts into the new sensor. Why is the voltage low? The ref volts at my TPS are exactly 5.0, which is correct.



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88 GTA 5.7 TPI Charcoal Grey Bone Stock except for loose muffler which makes it a bit louder than normal.

 

check for 5v across the conector and then from the yellow wire to battery ground. you probably have a bad ground.

 

From yellow wire to 'battery' ground, as in one of the grounds right next to the battery ? I was using the chassis ground. It makes a difference ? What about the starter ground ?
Going to check the battery ground now...


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88 GTA 5.7 TPI Charcoal Grey Bone Stock except for loose muffler which makes it a bit louder than normal.

 

From yellow wire to 'battery' ground, as in one of the grounds right next to the battery ? I was using the chassis ground. It makes a difference ? What about the starter ground ?
Going to check the battery ground now...


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88 GTA 5.7 TPI Charcoal Grey Bone Stock except for loose muffler which makes it a bit louder than normal.

 

I just checked the volts between the 2 terminals on the connector. 4.1 V. Checked the volts from the yellow wire to 2 different battery terminals. Again, 4.1. Everything is 4.1 Volts. This is with the connector unplugged, of course. So, what does this tell us ??? btw the Ohms at the sensor, between the two pins on the CTS sensor, are 2,400 at 25 degrees Celsius.

Thanks

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88 GTA 5.7 TPI Charcoal Grey Bone Stock except for loose muffler which makes it a bit louder than normal.

 

Unplug the TPS and MAT sensors and see if it goes up. If it does, one of those sensors is shorted pulling your 5V reference low.

If not, and since the TPS shares the same reference voltage and its good, then you have a bad wire between the Splice180 and the CTS connector.

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'87 Trans Am
S/D TPI retrofit including functional PassKey,
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Whatever chip I feel like burning,
JET AFPR, Ported Plenum,
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Flowmaster Exhaust,
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3.73 Posi
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Summit 1-5/8" headers, 2.5" Dynomax catback.

Best 1/8: 9.519@72.74

'97 Bonneville SSE

 

Do I have a MAT on this car? I do have a MAF and it is disconnected. I also disconnected the TPS and got the voltage at the CTS, which was still 4.1 BTW, the temp of my car was 70 F 21 C and the Ohms across the CTS were only 2,400. Is that sort of low ? Would that be consistent with a code 1t and running rich ? Is the CTS bad ?

Thanks



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88 GTA 5.7 TPI Charcoal Grey Bone Stock except for loose muffler which makes it a bit louder than normal.

 

The MAT screws into the belly of the plenum towards the back.

If the reference is low, then the CTS will read as though its really cold. If you completely disconnect it, it will register w/ the ECM as -44*F If the ECM reads the temperature as cold, it will dump fuel (like a choke on a carb). This is good when it actually is cold, but if its not cold, then its to much fuel and will run like crap and be rich. I am willing to bet that you either have a partially shorted MAT sensor, or the wire is broke inside the insulation. Tug on the yellow wire going to the CTS connector and see if your 4.1V doesn't change. Try moving other harnesses around also.

------------------
FREE CARFAX Record Check

If you live in Southeastern US, check us out!
South East Thirdgen

GM Master Tech
ASE Master Tech + L1
Savannah, GA

'87 Trans Am
S/D TPI retrofit including functional PassKey,
22# injectors,
Whatever chip I feel like burning,
JET AFPR, Ported Plenum,
TB Coolant Bypass, Custom Cold Air,
SSM SFC, KYB Shocks, Boxed LCAs, Wonder Bar,
8mm Accel wires,
Flowmaster Exhaust,
16" GTA rims,
Corvette Servo,
3.73 Posi
4wheel Disc Brakes
Summit 1-5/8" headers, 2.5" Dynomax catback.

Best 1/8: 9.519@72.74

'97 Bonneville SSE