LS-1st-Gen

Ok heres the deal. I have fans from a 97 Z-28, which have worked up to this point with my '98 relay. The fans used to come on as soon as i turned the key on, which I assume is because of the trouble codes I have not yet diagnosed (the car isnt on the road yet). I left my interior lights on over the weekend and the battery died. Ok so I recharged the battery, no problem, but now the fan doesnt come on when I turn the key on?? I read 12 volts at the fan plug, which should turn the fan motor on, and 13 at the battery. Is the one volt Im not getting the problem?? Or is the PCM now telling the relay to not turn the fans on??

-Gordon

LS1 PWRD

You should have 12v at the motor. The relay sets the ground for the fan motors and the PCM grounds the relay coil to energize the relay.

LS-1st-Gen

So apparantly the PCM isnt grounding the relay??

LS-1st-Gen

Now im just more confused, becuase Im reading both the ground and the hot at the terminals on the fan plug, Its like physically impossible that the fans arent coming on!!!! I know the motors arent burned up because i ran test wires directly to the battery and they worked fine????

-Gordon

Speartech

iTrader: (14)

I don't know on your particular harness, but normally the fan motors are permanently grounded. The fan relay provides the 12 volts when energized.
If you are seeing 12 volts at the fan plug at all times, it's probably a bad ground or some type of high resistance connection somewhere. Maybe just some feedback coming thru the relay.
My guess is that if you measure the wire somewhere besides the END of the plug, you'll see the voltage drop to zero as you plug the connector into the fan.

LS-1st-Gen

Ok john, I checked the voltage and as soon as i put a load on it, it dissapeared. Now what??? <img border="0" alt="[bang head]" title="" src="graemlins/gr_banghead.gif" />

Speartech

iTrader: (14)

Then go back to the relay, find the low side wire that goes back to the PCM (green wire on Speartech harnesses), and with the key on, physically ground that wire (small pierce with a pin or something) and with the key on that should make the fans run. By grounding that wire you are simulating what the PCM does when it turns the fans on.
If that all works ok, maybe you just reset the PCM when the battery went dead, and now the trouble codes that were set are gone, and not requesting the fan to be on.

Run the engine up to temp and see if the fans come on at the PCM programmed temp.

I really don't know why you see 12 volts on that fan plug when it's unplugged. That should be a completely open wire coming from the normally open arm of the fan relay, but I don't know anything about your particular relay or wiring harness.

John

LS-1st-Gen

John, thanks for your help so far..
I made the green wire to a ground and nothing happened, then i ran the engine to 220 and still no fans, then the engine died, which has me worried now. What do you think??

-Gordon

LS-1st-Gen

anyone have any ideas, cuz im stumped? Could the relay be bad?

-Gordon

Speartech

iTrader: (14)

It could be. How about a blown fuse?

It's easy enough to check the relay socket to determine if there is a problem there.

With the relay unplugged and the key on, you should have 12 volts at the "other" small wire beside the green.

What's left should be 2 big wires that actually power the fan. One of them should be hot with 12 volts. The other big wire is the actual wire that goes to the "+" side of the fan motor.

When the relay is activated, it connects the 2 big wires together causing the fan to run.

Either the big wire is dead (or has a bad connection where ever it comes from), or the little wire is dead, or the relay is bad.

If you were to take a short hunk of wire and jumper the 2 big wires together at the relay socket (with the relay removed) the fan motor MUST run. If not, the big wire is bad somewhere.

The little wire is what provides the 12 volts for the relay coil, and then the green wire gets grounded to complete that circuit. Intentionally grounding the green wire should make the relay click.

John

LS-1st-Gen

well i tryed jumping from the large red to the smaller one, and i got nothing. the fuse is fine so i guess its time to start looking for larger problems.

LS-1st-Gen

John, could this be a PCM problem? Or does it sound like wiring?

Speartech

iTrader: (14)

No, not the PCM. The only PCM interface is the GREEN wire, and when you pierce it and ground it with a piece of wire, you're doing what the PCM does.

The rest of the fan cicuit is simple power in, power out stuff.

I noticed in your last post you said you jumpered from the large red to the small red. The purpose of the test was to bypass the relay by jumping the 2 LARGE wires at the relay plug, to determine if the power wiring to the fan is good or not. I'm not sure you did that, but internet diagnostics is an uncertain thing at best!

John

LS-1st-Gen

yup, the large red is the 12 volts coming into the relay, and the smaller red (though still a larger wire) is the 12 volts going out to the fans. I purchased another relay yesterday, just for kicks, and like i thought, it didnt work.