Question about 1997 Chevrolet Suburban

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Decreased headlamp intensity.

My 1997 Suburban headlamp intensity is noticibly reduced. During night driving on rural highways, illumination on the roadway is dim even with "high" beams on. I can find no mention of adjusting the aim of the lamps in operator's manual. The lamp lens are somewhat "frosted".

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I have sucessfully used Mother's plastic polish on my 97 headlights and my 90 headlights and the bug shield on my 97. It cleans and polishes the yellowed plastic. I applied it with a mini-powerball in a cordless drill.

Posted on Sep 01, 2008

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My brake lights dont work most of the time, they illuminate when it wants to, intermittently, i have a 2004 Buick rainier, also my headlights work fine during the day, but at night when they want to.


Do you know anything about automotive electrical circuit testing ? Using voltage drop testing to find which part of the circuit has the problem , Voltage or ground side ? There is no common problem with both of these systems. After looking at a wiring diagram ,they have different grounds an B+ voltage supply's .
The STOP fuse in the engine wiring harness junction block supplies battery positive voltage to the normally open stop lamp switch. When the driver presses the brake pedal, the switch contacts close and battery positive voltage is supplied to both the VEHICLE STOP fuse and the VEHICLE CHMSL fuse. The current flow is now to the stop lamps which are grounded at G401 and G402. The center high mounted stop lamp (CHMSL) is grounded at G401.
For trailer wiring, a separate stop lamp circuit is connected through the GMSF to the trailer wiring harness.

Headlamps
The headlamp driver module (HDM) is an electronic module that provides electrical power to the vehicle low beam headlamps. The HDM is controlled by a pulse width modulated (PWM) ground signal from the body control module (BCM). The BCM determines the desired lamp intensity using the ambient light sensor, multifunction switch and the park brake switch as inputs. In general, the HDM will operate in 1 of 3 modes:
• Reduced Intensity Mode: This mode is used by features that do not require or allow maximum low beam headlamp intensity such as daytime running lights (DRL) (nominal: 85% duty cycle).
• Full Intensity Mode: This mode is used by features that require full low beam headlamp intensity such as low beam headlamp operation in manual or auto modes (nominal: 100% duty cycle).
• Off Mode: This is the default mode of the system that will occur when none of the features described above are active. The BCM will deactivate its PWM output (0% duty cycle) during this mode.

DTC B2575
When the BCM receives a ground signal from the headlamp switch requesting the low beam headlamps, the BCM will energize the HDM low beam relay by grounding the low beam relay control circuit.
For the brake light problem ,without testing , i would say there is a ground problem . Voltage drop testing the circuit would show what is wrong.


Mastering Voltage Drop Testing with Pete Meier and Jerry Truglia
Basic Electricity for Service Techs Ohm law Current Flow Opens Shorts
How to Use Multimeter to Troubleshoot Common Problems

Do you know what a wiring diagram is ? You need to look at one to see which wires to test . Free wiring diagrams here http://www.bbbind.com/free_tsb.html Enter vehicle info. year,make , model ,engine ! Under system click on lighting ,under subsystem click on exterior lighting . Click the search button ,then the blue links ! The fourth one down is the brake lights . You see the fuse's for the brake lights in the rear fuse box ? Do you know where that is located ? Fuse Block - Rear
Beneath the left rear seat.
Know as for your headlamps , probably the headlamp driver module is bad ! The headlamp switch is a input to the BCM - body control module . Hooking up a factory scan tool to view DTC'S - diagnostic trouble codes , an view input data to the BCM . To see if it is getting the signal to turn on the headlamps an see if it send PWM signal to the HDM .
Your best bet ,take it to the dealer .


Jun 29, 2017 | Buick Cars & Trucks

1 Answer

No low beam. Good high beam. No day lights. What's wrong?


No on the fuse . The LH HDLP and RH HDLP fuse in the fuse block - under hood, supply battery positive voltage to both low and high beam lamps at all times. For manual operation, when the headlamp switch is in the ON position, the headlamp switch supplies ground directly to the headlamps and to the body control module (BCM) on the headlamp low or high beam signal circuit, depending on the position of the headlamp dimmer switch. The BCM uses this signal to determine if the conditions are present to illuminate the daytime running lamps or park lamps.
The headlamps may be turned on 2 different ways. First, when the driver places the headlamp switch in the ON position, for manual operation. Second, with the headlamp switch placed in the OFF position activating automatic lamp control (ALC).For ALC operation, the BCM receives a signal from the ambient light sensor indicating a low or high ambient, outside, light level. Under low light conditions the BCM grounds the headlamp relay control circuit energizing the headlamp control relay. The now closed relay supplies ground through the headlamp switch to the headlamps and the BCM on the headlamp low or high beam signal circuit, depending on the position of the headlamp dimmer switch. When the BCM grounds the headlamp relay control circuit it also grounds the park lamp relay control circuit illuminating the park lamps. The headlamp relay is grounded at G203.
Daytime Running Lamps (DRL)
The low beam headlamps operate at reduced intensity when in daytime running lamps (DRL) mode. The ground circuit to the switch side of the DRL relay has a resistor in-line to reduce the intensity of the low beam headlamps for DRL operation. The body control module (BCM) receives a signal from the ambient light sensor indicating a low or high ambient, outside, light level. Under daylight conditions the BCM grounds the DRL relay control circuit energizing the DRL control relay. The now closed relay supplies ground directly to the low beam headlamps and to the BCM on the headlamp low beam signal circuit. The low beam headlamps now illuminate with reduced intensity. The DRL relay is grounded at G203. Any time the headlamps are illuminated the DRL will not illuminate. Manual park lamps do not effect DRL operation.

Feb 23, 2016 | 2005 Chevrolet Equinox LS

2 Answers

Headlight low beam on my envoy 2006 not working


The headlamp driver module (HDM) is an electronic module that provides electrical power to the vehicle low beam headlamps. The HDM is controlled by a pulse width modulated (PWM) ground signal from the body control module (BCM). The BCM determines the desired lamp intensity using the ambient light sensor, multifunction switch and the park brake switch as inputs. In general, the HDM will operate in 1 of 3 modes:
?€¢
Reduced Intensity Mode: This mode is used by features that do not require or allow maximum low beam headlamp intensity such as daytime running lights (DRL) (nominal: 85% duty cycle).


?€¢
Full Intensity Mode: This mode is used by features that require full low beam headlamp intensity such as low beam headlamp operation in manual or auto modes (nominal: 100% duty cycle).


?€¢
Off Mode: This is the default mode of the system that will occur when none of the features described above are active. The BCM will deactivate its PWM output (0% duty cycle) during this mode.

The normal battery voltage input to the HDM must be between 6 and 16 volts DC to operate. Any deviation to these values could cause improper operation.
Major components of this system are the BCM, HDM, ambient light sensor, multifunction switch, park brake switch and low beam headlamps.
DTC B2575 Headlamp Control Circuit
When the body control module (BCM) senses a request for headlamp or daytime running lamp (DRL) illumination, the BCM sends a pulse width modulated (PWM) ground signal to the low beam headlamp driver module through the low beam headlamp driver module control circuit. The low beam headlamp driver module will illuminate the headlamps, adjusting the intensity based on the PWM signal received
You best bet is to take your vehicle to a ASE certified repair shop or the dealer >

Jan 15, 2016 | GMC Envoy Cars & Trucks

1 Answer

2010. where is DRL module located?


Daytime Running Lamps (DRL) NOTE: The smart junction box (SJB) must be configured when installing a new module. For additional information, refer to Section 418-01 .
The DRL system operates the low beam headlamps at a reduced intensity. The SJB supplies pulse width modulated (PWM) voltage to illuminate the low beam headlamps at a reduced intensity when the following conditions are met:
  • The headlamp switch is not in the HEADLAMPS ON position.
  • The ignition switch is in the RUN position.
  • The transmission is not in PARK (P).
This dealer only repair ,unless you have the ford IDS (factory scan tool ) .

Nov 18, 2015 | Ford Explorer Cars & Trucks

1 Answer

2006 buick allure , automatic low beams do not come on when key starts car


Headlamps
You can use the headlamps two different ways.
?€¢
Place the headlamp switch in the HEAD position for normal operations


?€¢
Place the headlamp switch in the OFF position for automatic lamp control (ALC) operation. During ALC the low beam headlamps are ON for daytime running lamp (DRL) operation in daylight conditions at reduced intensity or low beam headlamps ON at full intensity with exterior park lamps ON in low light conditions. 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 just the low beam headlamps at reduced intensity for the daytime running lamp (DRL) operation. A resistor wire is used (CKT312) to reduced the voltage which reduces the light intensity for the DRL's function. The ambient light sensor can also turn ON the low beam headlamps and the exterior lamps for automatic lamp control (ALC). Any function or condition that turns ON the headlamps will cancel the DRL operation (this means no reduced voltage to the low beam lights). Thirty seconds after you start the engine with the headlamp switch in the OFF position, the DRL will perform one of two actions:
?€¢
Illuminate the low beam headlamps at reduced intensity in daylight conditions


?€¢
Illuminate the low beam headlamps and exterior park lamps for low light conditions

The DRL operates when the ignition switch is in the RUN position, the parking brake is not set and the transmission is not in the PARK position When these conditions are met and the DRL ambient light sensor indicates daylight conditions the DRL will illuminate
Should have BCM scanned for DTC'S - diagnostic trouble codes , could have DTC'S stored in memory !
DTC B2645 Ambient Light Circuit
The body control module (BCM) monitors the ambient light sensor signal circuit in order to determine if the daytime running lights (DRL) or the auto headlights (ALC) should be turned ON in the AUTO mode. When the BCM senses the ambient light sensor voltage is between 1.75-4.9 volts, either the DRL will be commanded ON or the ALC will be commanded ON.

  1. Turn ON the headlamps.
  2. Ensure that the headlamp dimmer switch is in the LOW position.
Do both low beam headlamps illuminate?
Is only one low beam headlamp inoperative? YES / NO
IF no
  1. Disconnect the lamps switch assembly.
  2. Install a jumper between the headlamp switch headlamps ON signal circuit and ground.
Do the low beam headlamps illuminate?
Do the low beam headlamps illuminate?
Go to Step 18
Go to Step 7

7

  1. Remove the headlamp module.
  2. Install a fused jumper between battery positive voltage and the switched low beam voltage supply circuit.
Do the low beam headlamps illuminate?
Go to Step 8
Go to Step 11

8

Test for the following in the headlamp module control circuit:
?€¢
An open


?€¢
A poor connection


?€¢
A short to ground

Refer to Circuit Testing and Wiring Repairs .
Did you find and correct the condition?
Go to Step 19
Go to Step 10

9

Inspect for a poor connection at the harness connector of the lamp switch assembly. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .
Did you find and correct the condition?
Go to Step 19
Go to Step 14

10

Inspect for a poor connection at the headlamp module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .
Did you find and correct the condition?
Go to Step 19
Go to Step 15

11

Test for a short to ground in the low beam voltage supply circuit. Refer to Circuit Testing and Wiring Repairs .
Did you find and correct the condition?
Go to Step 19
Go to Step 12

12

Inspect for a poor connection at the harness connector of the underhood fuse block. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .
Did you find and correct the condition?
Go to Step 19
Go to Step 17

13

Inspect the inoperative low beam headlamp voltage supply and ground circuit for a high resistance, a short to ground, or an open. Refer to Circuit Testing and Wiring Repairs .
Did you find and correct the condition?
Go to Step 19
Go to Step 16

14

Replace the lamp switch assembly. Refer to Headlamp Switch Replacement .
Did you complete the replacement?
Go to Step 19
--

15

Replace the headlamp module. Refer to Relay Replacement in Wiring Systems.
Did you complete the replacement?
Go to Step 19
--

16

Replace the inoperative low beam headlamp. Refer to Headlamp Assembly or Headlamp Bulb Replacement .
Did you complete the replacement?
Go to Step 19
--

17

Replace the underhood fuse block. Refer to Testing for Intermittent Conditions and Poor Connections .
Did you complete the replacement?
Go to Step 19
--

18

Replace the BCM. Refer to Control Module References for replacement, setup, and programming.
Did you complete the replacement?
Go to Step 19
--

19

Operate the system in order to verify the repair.
Did you correct the condition?
System OK
Go to Step 3

IF

Sep 30, 2015 | Buick Cars & Trucks

2 Answers

Auto headlights don't come on 2008 Chevy Trailblazer LT. What's the problem?


Maybe bad sensor as seen on the following video



And see how he troubleshoot it

Apr 15, 2015 | Cars & Trucks

1 Answer

2007 envoy the headlights on dim are not working


Did you check the fuse's an HDM relay #46 in the under hood fuse / relay box ?
Headlamps
The headlamp driver module (HDM) is an electronic module that provides electrical power to the vehicle low beam headlamps. The HDM is controlled by a pulse width modulated (PWM) ground signal from the body control module (BCM). The BCM determines the lamp intensity using the ambient light sensor, multifunction switch and the park brake switch as inputs. In general, the HDM will operate in 1 of 3 modes:
?€¢
Reduced Intensity Mode: This mode is used by features that do not require or allow maximum low beam headlamp intensity such as daytime running lights (DRL) (nominal: 85% duty cycle).


?€¢
Full Intensity Mode: This mode is used by features that require full low beam headlamp intensity such as low beam headlamp operation in manual or auto modes (nominal: 100% duty cycle).


?€¢
Off Mode: This is the default mode of the system that will occur when none of the features described above are active. The BCM will deactivate its PWM output (0% duty cycle) during this mode.

Mar 16, 2015 | 2007 GMC Envoy SLT

1 Answer

Low beams keep dimming while driving


Headlamps
The headlamp driver module (HDM) is an electronic module that provides electrical power to the vehicle low beam headlamps. The HDM is controlled by a pulse width modulated (PWM) ground signal from the body control module (BCM). The BCM determines the desired lamp intensity using the ambient light sensor, multifunction switch and the park brake switch as inputs. In general, the HDM will operate in 1 of 3 modes:
?€¢
Reduced Intensity Mode: This mode is used by features that do not require or allow maximum low beam headlamp intensity such as daytime running lights (DRL) (nominal: 85% duty cycle).


?€¢
Full Intensity Mode: This mode is used by features that require full low beam headlamp intensity such as low beam headlamp operation in manual or auto modes (nominal: 100% duty cycle).


?€¢
Off Mode: This is the default mode of the system that will occur when none of the features described above are active. The BCM will deactivate its PWM output (0% duty cycle) during this mode.

The normal battery voltage input to the HDM must be between 6 and 16 volts DC to operate. Any deviation to these values could cause improper operation.
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.
You should have the modules scanned for codes first off. Not the engine control module .( BCM ) body control module , yes . That's the first thing I always do !
Could be a bad ambient light sensor or the headlamp driver module. You could check voltage at the battery with engine running, should be over 14 volts. If you don't deal with this sort of thing on a regular basis I'd take it to someone who does !
You

Jan 08, 2015 | 2003 Chevrolet Chevrolet TrailBlazer

1 Answer

Dash lights go on and off while driving, then headlights do the same


Test the electrical circuit's ! Look at a wiring diagram so you know what wire's to test . Watch these video's , buy a DVOM - digital volt ohm meter . Learn to test so you don't listen to guesses .
Basic Electricity for Service Techs Ohm law Current Flow Opens Shorts
Mastering Voltage Drop Testing with Pete Meier and Jerry Truglia
Electric Testing Techniques You Need to Know Free wiring diagrams here . http://www.bbbind.com/free_tsb.html Enter vehicle info. year , make , model and engine size. Under system click on lighting ,then under subsystem click headlamps . Click the search button then the blue link's . Right away in the first diagram i see the headlamp / panel dimmer switch is a input to the BCM - body control module . I mite think your first response would be to want to replace the BCM ! Reading a discription of how the lights are suppose to work may shed some light on the problem .
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 class 2 serial data message from the BCM that the high beams are illuminated.

Having the vehicle checked for DTC'S - diagnostic trouble codes , BCM - codes ! Need a professional type scan tool . Part stores can't read body codes , dealer or independent repair shop .

DTC B2575
When the body control module (BCM) senses a request for low beam headlamp illumination, the BCM sends a ground signal to the low beam headlamp relay through the headlamp low beam relay control circuit. The headlamp low beam relay will apply voltage to illuminate the headlamps.
DTC B2580
When the body control module (BCM) receives a ground signal from the multifunction high beam or flash to pass (FTP) switch commanding to illuminate the high beam headlamps, the BCM will energize the high beam relay by grounding the high beam relay control circuit.
DTC B2600
DTC B2610
The body control module (BCM) receives a variable voltage signal from the instrument panel (I/P) dimmer switch requesting to illuminate the illumination lamps to a desired intensity. When this occurs, the BCM directly sends a variable voltage based on the I/P dimmer switch position on the instrument panel lamps dimming supply voltage circuit, instrument panel lamps dimming control circuit, and the LED dimming signal circuit.
Voltage for the instrument panel lamps dimming supply voltage circuit, instrument panel lamps dimming control circuit, and the LED dimming signal circuits is from the TBC 2 A fuse in the instrument panel fuse block directly through the BCM to these circuits.

DTC B2620
The BCM directly sends a 5 volt reference voltage to the I/P dimmer switch which is then adjusted based on the I/P dimmer switch position and returned as a dimming return and dimming input to the BCM. The BCM uses this signal to directly control the desired level of instrument panel illumination lamp intensity.

Your best bet , take it to a qualified repair shop .


Oct 23, 2017 | 2004 Chevrolet Avalanche

2 Answers

Daytime running light module location 2001 impala


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.

Oct 10, 2011 | 2001 Chevrolet Impala

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