Sorry about this being so long and I hope not too confusing.
OK. 1991 L98-Here's what I know. Both fans work, though the passenger side, the secondary according to the service manual, was a little slow starting up and squawk's at start up and low revs. It ran (sound wise) OK at speed.
I checked both at the relays by jumpering them both at the relays. I jumped both, one at a time, using the thick red from the battery in the relay harness, too their appropriate fan run wire. This worked with the left primary fan but not with the right, secondary. To get the right (noisy) secondary to run I needed a hot 12 directly from the battery. The 12 volt wire in the relay harness was dead.
Why would this be dead assuming the wire is solid?
Earlier I pulled the plug off the temp sensor under the throttle body (it's the only temp sensor I'm aware of and none are in the block, right 6&8 or left 1&3 locations) and jumpered the plug to see if the right fan would run with the key in the run position. Nothing. I also jumpered the A&B on the ALDL which ran only the left fan. Also when engaging the A/C only the left fan will run.
This leaves me thinking that maybe it's the temp sensor though I don't know why the ECM didn't allow 12 volts to get to the right fan when I jumpered it or else the ECM itself is bad (hope not).
Any help, direction or answers out there? Thanks, Frank :banghead:

 

The ECM should ground the grn/yel wire to either fan relay to turn on that fan.

With the engine running you should be able to ground either fan relay and bring on that fan. If not check that there is voltage at the relay output pin and at the fan. If not at the relay, replace the relay; if ok there but no power to the fan find the open in the power wire from relay to fan.

 

If your 12V source TO the relay is missing, somewhere there could be a break in the circuit. See if you can run a continuity test from the ECM end to the Relay end of the harness. Also, first check the maxifuses on the firewall (I believe your model year has them): 40 amp for the primary and 35 amp for the secondary.


[Modified by vetteseniorcit, 11:37 PM 4/15/2004]

 

I'm not following. I've got no grn/yel wire's at the relays. At the relays with the plug disconnected and with the key on I'm jumping the solid red (12 volt) in the plug to the blk/pnk (to the fan) on the secondary. Nothing happens because the red 12 volt is dead. When I jump the solid red and the blk/red in the primary fan relay, it runs. I can only get the secondary to run with a 12 volt wire directly from the battery to the blk/pnk of the secondary plug.

 

"somewhere there has got to be a break in the circuit."

Dosen't the ECM, getting a signal from the temp sensor, turn the secondary red 12 volt hot at the relay?

EDIT: As I'm thinking, apparently not! The ECM only grounds the relay therefore that aux fan relay 12 volt wire should have been hot and it wasn't as I've checked it.
Is there a fuseable link for that wire and where is it to be found.......???


[Modified by Frank C, 11:06 PM 4/15/2004]

 

I had a problem with my main fan not coming on and everything was working ok. I changed the fan relay twice thinking that was it but that didn't help. What i did was wire the aux fan to come on when the car starts and the main one i have a switch in the cockpit that i just flip and it comes on. What you can also do is wire the main fan to the aux fan wire by the sensor near the #4 plug and have it come on with the aux fan. Hopes this works.