97 Computer resets overnight, can't pass smog cause tests are cleared

the 97 4.3 5spd I just bought is having an electrical issue. The truck only has 24k miles so mechanically should be pretty sound.

I pass the sniffer test for CA smog, but the computer diagnostics must clear all the sensor tests. Problem is when I start my truck in the morning to go get it smogged, all these tests are cleared, as if I disconnected the battery. I can drive around for 50 miles or more to try clear the sensors, but I couldn't get the evap and O2 heater sensor tests to compete. I think Evap was cause I had a full tank of gas (I read needs to be 1/4-3/4) and the O2 sensor heater is cleared when you start the vehicle up cold, let it idle for 2.5 minutes with AC on. For some reason I haven't got the O2 sensor heater to clear, I think cause it's been so damn hot here last couple days (98deg) that it wont trigger the test cause the IAT and coolant temps are more than 11 deg apart.

Anyways trying to diagnose why the computer is losing power. I bought a scanner tool and it said battery is 11.7-11.9 which is too low. I starts up and drives fine but I guess maybe it's on its way out. But you would think if it has enough power to crank the engine it would have enough power to maintain computer memory? Does anythink a low batter could actually cause computer to lose memory overnight? I have a good battery in my 98 blazer I can swap in to test, or ill probably just buy a new battery since ill be needing one anyways.

If the battery doesn't fix it, where would you guys look next? which wires can I check for battery power going into the computer? it's obviously getting ignition power cause the truck starts and runs.

Ok update, took the truck to pepboys to have battery tested it. 12.47, barely under the 12.5 standard. The tester refused to charge it, said it's bad.

Then I saw it had a 8/16 sticker on it. Called the guy that sold me the truck, asked him when he replaced the battery. He said last month. So a brand new battery is killed in a month. I think it's the electric fans that might not be wired correctly. The fan goes directly to the battery, it will run for a good minute or so when you shut off the vehicle. Shouldn't it be connected to a switched/ignition power source?

I'm not sure which electric fan it is, it's tucked into the factory shroud neatly, this weekend I will have time to dive in and check where its wired, maybe there is a relay I didn't see?

so I think the relay is built into the fan.

Here is a picture, I unplugged the red wire that went to the "B" terminal and the blue wire going to the "C" terminal just for picture clarity. There are two more wires going to the  "G" and "+", the "M" terminal does not have anything connected, I believe that is for the manual over ride switch?

Can anyone identify this fan from the relay picture I've posted? the relay is integral to the side of the fan assembly. I cant take better pictures without removing the fan shroud.

I'm guessing the + is for a switched power source as B you would think goes to the Battery. Without taking anything apart the only thing I can confirm now is the B does in fact go to the battery (there is a fuse inline too).

It's been really hot here, upper 90s last few days. And truck was in Vegas before this which is even hotter. The fan will run for over a minute, up to 2 minutes I think, I haven't really timed it, after I shut off the vehicle. This seems pointless as the coolants no longer flowing and if I still had the factory engine driven fan that would turn off as well.

Am I correct in thinking this fan should turn off when the truck is keyed off? Maybe they ran the + direct to the battery as well instead of a switched power source. That being said, where would be the best place to pick up switched power? the relay is on the left side of the fan, close to the battery.

I know I'm just talking to myself here, but hopefully this will help others if they run into the problem.

Found out this is the old discontinued flex a lite S10 specific kit.

I was right, the + is supposed to go to an ignition controlled 12v source. It's clearly not since it continues to run after the truck is shut off.

So I'll rewire this tomorrow, toss in a new battery, drive a hundred miles or so until I can clear all the OBD2 diagnostic tests. and hopefully this fixed the computer losing it's memory....

Well the final verdict was the battery and electric fan being wired incorrectly. Autozone replaced a battery only 4 weeks only, it would not charge above 60% or 12.45v. It would fall as low as 11.9v in the car from by obd2 scanner tests.

Rewired the fan, installed a 15amp fuse (fan wire was 14awg) on the battery supply and ran the 12v switched for the relay to the yellow power wire on the windshield wiper motor. Fortunately it rained that day so I was able to test that the fan and the wipers work no problem even though I wasn't expecting a problem with the relay current draw being so low.

I'm still surprised that the computer memory needs higher voltage than the engine does to start.

Passed smog no problem on Tuesday. Of course CA DMV offices have been offline the whole week due to a state wide computer failure of course... One day soon I'll get her registered.

Don't forget while starting the voltage will drop due to the demands of the starter, so it may be fine at 12V, but drop below what the PCM requires as the starter engages. In similar fashion I had a quality project at work where a vehicle module would read an erase command because of the change in voltage during a vehicle start.

Glad you found the problem(s), though. Electrical gremlins aren't always easy to sort out even in our older trucks.