Buick Roadmaster Drivers Side Fan Not Coming On.

[loganlanguet]

Earlier in this post, a member posted this diagram, which is the correct diagram for my car. View attachment 49340

My buddy who is a mechanic told me to test from battery ground to the B4 terminal on the primary relay. If that isn't getting power its part of another circuit thats the problem. And seeing as there was no voltage on any pins. My guess is thats whats going on.

 

[RD_Atlanta]

Right, terminal B4 should have 12v anytime the ignition switch is on. Double check that you do not have 12v on B4 with the ignition switch on? If you are certain there is no 12v at B4, the problem is on the the sourcing side of this circuit (which simplifies your troubleshooting this issue). You will need to then work upstream of B4 to find where the open circuit is. The most probable suspect is fuse 7 (be sure that you have voltage on each side of fuse 7 under the hood when the ignition switch is on).

 

[HotZ28]

The thermostat is located below the throttle body & air intake elbow. The PCM controls the fans based on the information from the CTS. I still don't see that you have replaced either the thermostat, or the temp sensor???

 

[loganlanguet]

The thermostat is located below the throttle body & air intake elbow. The PCM controls the fans based on the information from the CTS. I still don't see that you have replaced either the thermostat, or the temp sensor???

No I havn't. The temp sensor tested good. There is the one in between plug 6-8 that I havn't checked. The thermostat is working properly from what I can tell, because when the engine gets to 230 degrees the secondary comes on. I just dont want to buy all of these parts and it be a simple issue.

 

[Riskit]

Again, I’m not 100 but you’re not getting power to relays because it’s fed with a negative trigger not positive. The pcm/ecu sends a negative trigger to open relay