I have a 1987 vette that has started running poorly and displaying the check engine light. Checked the code (15) and replaced the CTS now I still have the same problem but with code (14) anyone ever encounter this ?

 

here are few pages from the factory service manual with trouble shooting steps for each error code. Compliments of AGENT86

http://members.shaw.ca/corvette86/Code%2014.pdf

http://members.shaw.ca/corvette86/Code%2015.pdf

 

Codes mean a fault within that whole system ; not just a problem with the actual sensor itself in that system.
Need to check wiring / connections / grounding etc as per the pdf's in links posted above

 

Get a voltage reading on the yellow wire with everything connected. Either puncture with a pin or skin the wire back. A reading of 0 or 5 volts would be no good. Depending on the temperature and resistance of the CHT, the voltage should be somewhere in the middle of the range. Three or four volts possibly when cold. If you get a reasonable reading then the ECM might be giving you a false error code.

If the voltage is not there at all, the ECM or wiring back to it might be the problem.

 

Replace the suspected sensor with a original GM part.
I have had them test good under load and still be bad.

 

Thanks everyone for such quick responces I'll let you know what I find

 

I wouldn't puncture anything on this circuit as it relies on resistance to calculate voltage drop. Exposing the copper wire to air will increase resistance and skew the calculation which is used to determine how much fuel it needs.

Sensor is simply a Thermistor meaning it's resistance decreases as it heats up. 5 volts is the reference from the ECM (yellow wire) and should be present with the harness disconnected at the Sensor. Resistance determines how much of that 5 volts reaches ground. The resulting voltage drop equals coolant temperature.

The 15 meant none of the voltage reached ground - Connector disconnected; not making good contact or a dead ECM. If you scanned it, you'd see -38 degrees as the coolant temp.

The 14 means all of the voltage is going to ground. A scan would show 300 degrees. The Reference wire is either touching the black wire (ground) - look inside the Connector at the Pins or the Yellow is grounded somewhere in the engine compartment.

Sensors rarely go completely bad (to generate either code), but they can become weak; increasing or decreasing in resistance as they age. You check the sensor out by measuring the resistance across it's terminals and for any outside air temp, your Service Manual shows you what the resistance should be.

New Sensors usually come with a New Connector that can be spliced in (and it sounds like your Connector needs some work), but again, be mindful of resistance and use some solder on any splice that you make and wrap it up with some automotive (high temp) electrical tape or use some heat shrink.

 

Okay ran the diagnostic checks from the factory service manual links and it pointed back to the sensor, replaced the sensor again and no more codes and she's running great again.
Thanks again to everyone who responded, I couldn't have done it without you !!!!!