check engine codes 13,14

My 91 sse showing codes 13 and 14. I have changed the thermostat and the temp sensor. I tested the O2 sensor, it appears to be sending the proper signal. The check engine light comes on after the car warms up. I don't know what else to check,the wiring looks OK. Any ideas??:confused:

Wiring could have been involved, but you have it checked out already. ANy other symptoms, any at all, that you would find abnormal? Sometimes, rather often, sensors send a code as a consequence rather than indicating the actual cause. Any loss of coolant ?

That is almost always a bad o2 sensor.

Did code 14 come back after the sensor was changed?

I agree with Max....code 13 "usually" is the O2 sensor....

There is only one way to test an O2 sensor and that is with a scan tool.....don't know how you "tested" it......

Thanks for the response. No coolant loss and the temp is normal. I tested the O2 sensor by conecting a meter to the sensor wire(it has only one wire) and read the DC voltage output. It cycled between .2 nd .7 volts with the engine warm. I realize that this test is not conclusive and the voltage is hard to read with the numbers jumping around. Is there anything else I can look for ? Just wondering if it is the o2 sensor why I'm getting the high temp code. I think 13 is for O2 sensor open and 14 is for coolant temp high.
Going to replace the sensor ,I will post the result. Thanks for the help.

Do not use Bosch, Standard on this car....

Denso, NTK and AC Delco are ok...

Well I replaced the oxygen sensor. Took the car out for a drive and the check engine light came on again as soon as it warmed up . The car runs fine and the gas miliage seems normal. I am the original owner and I've had very few problems with the car. What can I look for now?
A visual inspection of the wiring didn't find anything. The light comes on only after the car warms up. :confused:

You don't say what code came back, the 13 or 14?

As I said there is only one way to check an O2 sensor, and that is with a scan tool......

First, you start the vehicle, and then disconnect the O2 sensor....the scan tool reads around 450mv......now install a jumper in the harness side to the ECM.....grab the other end of the jumper with one hand, and then with the other hand, touch the neg terminal of the battery....scan reading should drop towards 0.100mv.....now touch the pos terminal.....should go to 0.900mv....if it does, the circuit to the ECM is ok...if it stays at 0.450, you either have a bad circuit to the ECM, or bad ECM, or bad sensor ground to the ECM....

Now attach your new O2 sensor.....it should be constantly changing(once it warms up) above and below 0.450mv.......if it isn't, then there is a problem.....a vac leak could cause it to run constantly lean(especially one near the exhaust)......a rich condition could cause it to constantly read above 0.450(like a dirty air filter).....

Both 13 and 14 codes came back,just like before. There is no exhaust leak,system replaced from convertor back. Air cleaner filter is new. I don't have a scan tool . Is there anything else I can do?

Disconnect the battery for a minute and reconnect...

Check and see if any codes come back( do not start the engine, just turn the ignition on ) There should be no codes present, should just get the handshake code 12 over and over...

Did as suggested the positive cable,codes cleared for now. I did disconnect the battery ground cable when I replaced the O2 sensor, I didn't check if they were gone then. Would the ground removal clear the codes?
I will test drive it to see what happens. Starting to lean towards ECM problem, hope I'm wrong.

Disconnecting either cable clears the codes, you may need a full scan to look at o2 activity rather than continue with guesswork.