The low beams are powered by a separate Lo Beam relay located in the under-hood fuse block (see attached diagrams). The relay is actually controlled by the Body Control Module(BCM) who receives a signal from the headlamp switch. To determine what's causing the issue, we'll need to start by testing the relay to make sure it's getting what it needs to operate properly. See the link below for more specific information on relays and how to test them. Once the relay is removed, you'll need to make sure we have 12v at terminals 30 and 86 or 85. See the link below if you're unfamiliar with the use of a test lamp. Assuming you have power at these locations, we can perform a quick easy test to confirm the low beam circuits themselves are working. Using a small piece of wire with both ends stripped, insert it in terminals 87 and 30 of the the relay socket in the fuse panel. This jumper should cause the low beams to activate. If they do, we know there is an issue with the control side of the relay.
Next we'll need to see if the BCM is commanding the relay to turn on. Previously you checked for power at terminals 86 and 85. Only one of them should have had power. The other one is the BCM control circuit. At this point, take a test lamp and connect the clamp lead end to the positive battery terminal. Next, turn on the headlamp switch. Now, touch the test lamp probe to which ever terminal(86 or 85) did not have power in the previous test. If all is working correctly, the test lamp should illuminate. If not, the BCM most likely has an internal failure and will need to be replaced.
Test Lamp Operation
https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester
Relay Testing
https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit
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Monday, July 27th, 2020 AT 5:33 PM
