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99 chevy 1500 with DRL feature; headlights won't come on when truck is started. Headlights can't be turned on manually either. Checked ambient light sensor, relay switch and fuses. Parking, turn signals, brake lights and fog lights all work. Have read the DRL disable suggestions but nothing about headlights failing to coming on, Ambient light sensor appears to work fine.
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the car has smart bcm (ALC) and key off 10 mnutes later headlamps turn off all by them selves.
so you did not say key is on.
if key is off and want HL , turn key to accessory pos.
there are a pile of fuse to be bad for ALC,DRL
why not just scan the PCM see the errors?
there are 4 Silverado's, 1500 to 3500, sorry no ESP today.???
not told do you have DRL lamps, as seen in CANADA not USA 2011
no engine told, gas and diesel not wired the same at all so
why not just post the VIN so I can tell you what you drive and RPO list too.
ok, we check all fuses no just 1 or 2.
learn that modern cars use a network (called can-bus)_
and if 20 other fuse blow the can bus can fail
so not scanning the PCM first is super bad idea. see why?
1500 (roll dice land)
there are 6 DRL fuse and 4 relays. see?
I guess you have ACL, per this page 1 ,in front lamps
heads
The headlamps may be turned on in 2 different ways. First, when the driver places the headlamp switch in the HEADLAMP position, for normal operation. Second, with the headlamp switch placed in the AUTO position, for automatic lamp control (ALC). During ALC the headlamps will be in DRL operation in daylight conditions, or headlamp operation in low light conditions.
Headlamp ON/OFF control is determined by the body control module (BCM) by a signal on the headlamp switch on input circuit when the headlamp switch is in the HEAD position. When the headlamp switch is in the AUTO position, the BCM determines headlamps ON/OFF by the voltage from the ambient light sensor.
If the headlight switch is left in the ON position, the inadvertent power control feature will turn off the headlights approximately 10?minutes after the ignition switch is turned to the OFF position. If the driver places the headlight switch in the ON position after the ignition switch has been turned OFF, or if the ignition switch is in the ACCY position, the headlights will remain on until turned off or the battery runs dead.
The high beam indicator is illuminated when the instrument cluster receives a GMLAN serial data message from the BCM that the high beams are illuminated.
I still; call fuses bad
low beams dead driving is hard hard failure.
and many fuses for ALC
the service manual covers all this.
That piece you think is a ceramic DRL module is a resistor , When in DRL mode voltage to the low beam headlamps circuit goes through that resistor dimming the headlamps from low beam to daytime running lamps . It sounds to me like you need a new resistor ,but without doing some electrical testing it could be a lot of things . The DRL relay in the under hood fuse box could have a problem , could be the BCM - body control module , the ambient light sensor etc... Here is how daytime running lamps work .
Daytime Running Lamps (DRL)
The ambient light sensor is a light sensitive transistor that varies its voltage signal to the body control module (BCM) in response to changes to the outside (ambient) light level. When the BCM receives this signal it will either turn on the daytime running lights (DRL) or the headlights. Any function or condition that turns on the headlights will cancel the daytime running lamps operation. With the headlight switch in the OFF position, the headlights will either be turned ON or OFF, after an approximate 30 second delay depending on whether daylight or low light conditions are sensed. The HTR A/C IGN fuse in the underhood junction block supplies ignition positive voltage to the daytime running lamp (DRL) relay coil circuit. The DRL relay switch contacts are connected to the low beam circuit. When the headlamp switch is placed in the OFF position, the BCM will either turn on or off the daytime running lamps, depending on whether daylight or low light conditions are sensed. The BCM energizes the DRL relay, closing the switch contacts and grounding the low beam circuit. Ground is provided at G101. The DRL illuminate the low beam headlights at a reduced intensity. The DRL will operate when the ignition switch is in the ON position, the gear selector is not in the PARK position and the parking brake is released. When these conditions have been met and the ambient light sensor indicates daytime conditions, the DRL will illuminate.
In the 1999 Chevy Silverado 1500, the headlights are not designed to be on all the time by default. They are typically controlled manually by the driver using the headlight switch, although some vehicles may have a daytime running lights (DRL) feature. If the headlights are continuously on, it could be due to a modification or wiring issue, and it's recommended to consult the vehicle's manual and seek professional assistance if needed.
The daytime running lamps in your 2001 Chevrolet Impala are controlled by the Body Control Module (BCM) Here is a description of how the system works:
The ambient light sensor is a light-sensitive transistor that varies its voltage signal to the Body Control Module (BCM) in response to changes in the outside (ambient) light level. When the BCM receives this signal, the BCM turns ON either the DRL or the headlamp relay for auto headlamp operation. Any function or condition that turns ON the headlamps will cancel the DRL operation. Thirty seconds after you start the ignition with the headlamp switch set in the OFF position, the DRL will perform one of two actions:
Illuminate the high beam headlights at a reduced intensity in daylight conditions Illuminate the low beam headlights in low light conditions The DRL/EXT lamps fuse in the top of the engine fuse block supplies battery positive voltage to both the DRL switch contacts and to the DRL relay coil. When the BCM energizes the DRL relay coil, current flows through the right high beam lamp, to the left hand high beam lamp, to the energized DRL relay switch contacts, to ground G101. The high beam headlamps are now in series, and split the voltage so that the headlamps illuminate at halt intensity. The DRL operates when the ignition switch is in the RUN position, and the parking brake is not set or the transmission is not in park. When these conditions have been met and the ambient light sensor indicates daytime conditions, the DRL will illuminate.
Daytime Running Lights (DRL) feature only activates the front low beam headlights. The rear parking light are not turned on by the DRL, they only come on in dark conditions or by selecting the light manually.
The wiring for these headlights is complicated. The body control module (BCM) controls whether the headlights should be on or off depending on the ambient light sensor readings. Your headlight switch should override this if switched to on - if it doesn't do this, the headlight power relay may be faulty.
The daytime running lamps (DRLs) are also controlled by the BCM and a DRL relay, also controlled by readings from the ambient light sensor. If they will not come on, the DRL relay may be faulty.
However, the root cause could be a fuse, faulty light sensor, headlight switch, or BCM. I would start by checking the fuses and checking/replacing the two relays.
WHAT YOU MIGHT CHECK IS THE FUSE FOR TAILLIGHTS, OR DASH LIGHTS. THEY WORK OFF THE SAME FUSE. IF THE FUSE IS BLOWN THE HEADLIGHTS WORK BUT NO TAIL OR DASH LIGHTS
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