1996 Z28 No fan operation. Fans will work with the AC on and when I trigger a SES light (unplugging MAF sensor). I verified all relays and fuses are good. I grounded the fan wires on the passenger side and they work fine like that. I reset the PCM many times. I verified 5v at the PCM temp sensor. When I jump the pins on the DLC according to shoebox's method they do not work. So, I bought a scanner and scanned it this evening. I let it get to 228.2 degrees and no fans. The gauge was in the red, just a little though. Then I shut it down after turning the AC on to bring the temp down.
MY questions are : Am I correct to assume my PCM is bad? Do I need a new one or can a mail order tune repair this issue? How do I determine if the PCM temp sensor is bad? It is in a really bad spot to try to check the resistance and I don't want to drain the coolant for no reason. Is it also safe to assume the temp sensor for the gauge is bad also(I inspencted the harness for damage or burns and I did not see any)? Are the PCM sensor and the gauge sensor the same? Any part numbers for the sensors and a economical place to get them?
Kinda of the subject, but when I scanned the PCM, it said that it was OBD CALIFORNIA. I am assuming that means it is a CA car, but does that mean I have a different tune due to the stricter emissions? Any HP or performance loss?

 

Check the engine coolant temp sensor used by the PCM which is a different sensor then the one used for the gage. It's located in the water pump. If you had a scanner, you could monitor the temp. If not, measure from the clear or grey PCM connector pin 25 (it has a yellow wire) to the black PCM connector pin 6 (it has a black wire) while at normal operating temp. with power on and the PCM connected.

It should read 1.5 to 2.0 volts DC.

 

You should of let it get a little higher than 228.2°. Sometimes there is a little lag in the time it reaches the ON temp threshold and when the fans actually come on.

 

I am a little nervous about it getting any hotter. The scanner reads 228, but the gauge is in the red. I don't if the guage is wrong or the PCM temp sensor is wrong or both. If the PCM is seeing 228 and the PCM sensor is bad, it really could be 250 for all I know. I cant believe both sensors are bad at the same time. The PCM sensor is around $30 and the Gauge sensor is around $35 from the local parts store. $65.00 is a lot to be guessing at what is bad. Would either one being faulty trigger a code? The code scan is clear.
If it is a bad PCM would a tune fix it or does it need to be replaced. I am confused why the fans don't run when I jump the DLC. Does that indicate a bad PCM or a bad temp sensor? Thanks for the input.

 

About the only time a DTC is caused by the sensor for the PCM is if it keeps showing a low temp.
Not sure why the fans don't come on when you jump the DLC, unless you are doing something wrong. PCMs rarely go bad, but sometimes they do.
You can check the sensors with a meter and maybe use an infrared temp gun as a third source for confirming temp.

 

I used the instructions on your site for OBD II - 1996. Anything else I can check?

 

Did you check to make sure pin 5 has a ground on it? And for that matter, that pin 6's wire has continuity to the PCM? (you should see 5v with the key on)

 

You say "fans work with AC on".... but are you sure they are operating at low fan speed. 226*F only triggers the fans to run at low speed. Has to reach 235*F ro them to go to high speed. Perhaps you have a problem with the low speed circuit.

Have you checked both temperature sensors, per Shoebox's instructions? Do they both show the same resistance when the two locations are at the same temperature (several hours since the engine was run).

 

they are running at low speed with the ac on. I grounded the connector wires on the passnger side and I verified both high and low speed work. I am going to check my voltage on the DLC pins like shoebox suggested and verify the sensors this evening. Thanks for all the help so far!