Question about 2004 Chevrolet TrailBlazer
Replaced relay last year, could this be problem again?
Of course it could, the relays only last so long and some times the store bought ones last less time than the ones bought from the dealer.
Posted on Nov 26, 2008
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When the headlamp switch is in the AUTO position, for automatic lamp control (ALC)
When the headlamp switch is placed in the AUTO position, with the windshield wipers ON in daylight conditions, after a 6 second delay
Battery voltage is applied at all times to the coil and switch sides of the LOW BEAM PCB Relay located in the underhood fuse block. When the headlamp switch is placed in the HEAD position, ground from G202 is applied through headlamps ON switch signal circuit to the body control module (BCM), signaling the headlamps ON request. In response to this signal, the BCM applies ground through the headlamp low beam relay control circuit energizing the low beam relay. With the relay energized, battery voltage is applied through the switch side of the relay, the left and right low beam fuses, and the low beam supply voltage circuits illuminating the low beam headlamps. Ground for the left headlamp is provided at G101 and the right headlamp at G100.
Low Beam Relay Test
If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.
Connect a test lamp between the supply voltage circuit terminal A and ground. Ignition ON, command the Low Beams ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
If the test lamp is always ON, test the supply voltage circuit for a short to voltage. If the circuit tests normal, replace the underhood fuse block.
If the test lamp is always OFF, test the supply voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the underhood fuse block.
If all circuits test normal, test or replace the low beam headlamp.
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