2004 Impala dim odometer

[dorlow]

Hi, does anyone know how to fix a dim odometer on a 2004 Impala LS? I replied asking on another thread that was for a 96 originally and someone replied saying I need to reply on the 2000 and up Impala forum. As much as I know, there's only one Impala forum. But the odometer is really dim. When my lights turn on, it gets a little more dim and the knob controls the dimness. When the lights turn off, then it still stays dim, but the knob doesn't control the dimness anymore. My first thought was the car thought the lights were still on, but seeing the dim controls don't adjust it when the lights aren't on is my reasoning that isn't true. Is there a resistor I need to resolder like the 96 forum said needed to be done? If so, does anyone have detailed instructions or pictures showing exactly what needs to be done? I like to know exactly what I'm looking for and what I'm doing before I start a project.

[dorlow]

Anyone have any ideas? My radio is the same dimness... so it isn't the odometer that is just wearing out. During the day and early evening, you can barely see either the odometer or radio. It isn't too big of a deal for the odometer... but I like to see the channel or what time it is on the radio.

[ken729]

Voltage (12v) to the dimming control originates at the 15 AMP fuse for the Rear Parking Lamps and is varied by the dimming slider ( variable resistor) located next to the head lamp switch. If the dmiming slider is not functioning properly and is providing too much resistance in the circuit it could keep the lamps dim. Assuming your rear parking lamps work at proper brilliance, I would next probe the power line to be sure 12 volts is reaching the dimmer. My circuit information says its the brown wire with the white stripe at the headlight switch. If +12 volts ( or slightly above) is present I would suspect the dimmer slider is not passing the full 12 volts on to the bulbs. If some other voltage much less than 12 volts is present there could be a problem with the wire from the fuse is damaged, broken or poorly connected.

Additionally the BCM is involved in the logic to the dimmer board providing on or off ( but not variable) dimming through its class 2 communications bus. This also could be the problem - but I would start with the above.

[dorlow]

Well, my dimmer is in the headlight switch itself.. not next to it. The knob you pull out to turn on and off the lights also twists to dim the dash. But it makes sense that something went wrong with that and the dimmer and thing you pull and push to turn on and off the lights, something is wrong with that. So, I need to replace that, correct?

[dorlow]

If it's the case that my headlight switch is bad and needs to be repalced to fix the brightness of the radio and odometer, would that also explain why it seems like my headlights are dimmer than usual lately too? I just thought it had to be my imagination. Would the headlight switch have anything to do with how bright my headlights are? Extra resistance in the switch would cause them to be dimmer? The car's lights turn on automatically when it's dark out, so I'm not so sure if the headlight switch would have anything to do with it. While I was driving to work, I turned the light switch on to see if they got any dimmer or brighter with the light switch on vs off and it was the same.

[ken729]

The BCM plays also role here as I mentioned. Do yoiur automatic lights work properly? Check your owners manual to see how yours should be working. In my 2000 LS the outer bulbs illuminate at night and the inner bulbs for high beams illuminate during the day (DRL). They are controlled by a small dashboard sensor that monitors outside ambient light levels for the BCM. At the same time , this sensor,via the BCM, also dims the panel/radio bulbs at night and fully illuminates them during the day. If the sensor is disconnected or not working your car may think its dark out during the day by illuminating the outer headlight bulbs and dimming the panel/radio all the time. As I said - check your book to see how yours should work -it might be the same but I'm not certain.

[dorlow]

The sensor is working. The lights outside the car are not on during the day. I hear the lights click on and off when the sensor senses it's night or day. I do see a difference in the displays when the car thinks its day or night... but it's just too dim when it's day. I'm 99% sure it was much brighter when the car was new.

[ken729]

Ok - if the automatic lights are working properly as you described, I would go back to suspecting the headlight switch/dimmer. First, I would check to be sure that the Rear Parking Lamps illuminate to full brilliance. (The voltage that goes to the dimmer switch originates from that same +12 volt DC circuit fuse according to the schematic). If not, check the fuse - my 2000 LS fuse for this ciircuit is located in the Passenger Side Instrument Panel Fuse block. Check your manual for the location - might be the same - I'm not sure. If the Rear Parking Lamps Illuminate correctly then I would proceed to probe the circuit as I described earlier for voltage reaching and leaving the actual headlight dimmer switch. That will tell you whats going on for sure. If you dont have a voltmeter or are not comfortable probing the circuit you could just try replacing the switch/dimmer module. I'd try to get a used one or one from a junkyard in that case

[dorlow]

Originally Posted by ken729

Ok - if the automatic lights are working properly as you described, I would go back to suspecting the headlight switch/dimmer. First, I would check to be sure that the Rear Parking Lamps illuminate to full brilliance. (The voltage that goes to the dimmer switch originates from that same +12 volt DC circuit fuse according to the schematic). If not, check the fuse - my 2000 LS fuse for this ciircuit is located in the Passenger Side Instrument Panel Fuse block. Check your manual for the location - might be the same - I'm not sure. If the Rear Parking Lamps Illuminate correctly then I would proceed to probe the circuit as I described earlier for voltage reaching and leaving the actual headlight dimmer switch. That will tell you whats going on for sure. If you dont have a voltmeter or are not comfortable probing the circuit you could just try replacing the switch/dimmer module. I'd try to get a used one or one from a junkyard in that case

I don't mind using a DMM, but I'm definitely not an electrical engineer. I know enough to be dangerous. I can do some small wiring around the house and in the car.

My first thought I think I'm going to try is take the dash apart and just remove the connector to the back of the light switch so I take it out of the equation and the resistance it's putting on the circuit. Theoretically I could just leave it that way if it works, seeing I never use the light switch... except I won't have a way to adjust the dimness of the display at night... so maybe it won't work. I don't know.

What kind of tollerance am I allowing when checking the circuits with the DMM?

[ken729]

I read your initial post again and then I checked to see how my 200LS works - during the day I don't see any illumination of the odometer or radio buttons - just the channel display is fully illminated, When the automatic headlights go on when its dark out , the odometer and radio buttons illuminate while the channel display ( ie 104.7 or whatever) dims a bit. The only variable dimming of the panel/ radio buttons my vehicle has is when the headlights are on at night. If you are experiencing dim lighting of the radio display during the day, that is symptomatic of the automatic head lights being on on durng the day. This exact scenario happened to me last summer when the connector to head light sensor in the dash came off. I could hardly see the radio display during the day. There are most likely other causes of this, too ( ie dirty sensor cover).

To answer your question about tolerances using a multimeter, if your battery voltage when the car is off for a few minutes reads 12.5 volts DC or thereabouts, then your test voltages when the car is off should be very close to that. Problems with night time excess variable dimming still point to the headlight/dimmer switch or low circuit voltage being at fault.

Good luck.

[dorlow]

Originally Posted by ken729

I read your initial post again and then I checked to see how my 200LS works - during the day I don't see any illumination of the odometer or radio buttons - just the channel display is fully illminated, When the automatic headlights go on when its dark out , the odometer and radio buttons illuminate while the channel display ( ie 104.7 or whatever) dims a bit. The only variable dimming of the panel/ radio buttons my vehicle has is when the headlights are on at night. If you are experiencing dim lighting of the radio display during the day, that is symptomatic of the automatic head lights being on on durng the day. This exact scenario happened to me last summer when the connector to head light sensor in the dash came off. I could hardly see the radio display during the day. There are most likely other causes of this, too ( ie dirty sensor cover).

To answer your question about tolerances using a multimeter, if your battery voltage when the car is off for a few minutes reads 12.5 volts DC or thereabouts, then your test voltages when the car is off should be very close to that. Problems with night time excess variable dimming still point to the headlight/dimmer switch or low circuit voltage being at fault.

Good luck.

I explained in one of my prevous posts that I know for sure my lights are not on during the day and the displays are still dim. So, it's not the sensor that tells the lights to turn on and off. And I know it's not that the displays are just worn out either... the radio is new. When I bought my car, I put an aftermarket radio in it. After a few years, the after market broke. I recently bought another factory radio and replaced the after market with the factory radio again. The odometer and new factory radio are both the same dimness, so it's not the displays just old and worn out. Something is telling it to be dim. But the lights are not on. I can hear it click when the lights turn on. When the lights are off, when turning the knob, it doesn't change the dimness of the display like it should if the lights were on. I've gotten out and verified they're not on. It's not the day/night sensor in the dash. It's something else. The only thing that makes sense to me is the on/off switch that turns the lights on and off, because the knob turns and causes the dash to go brighter and dimmer... which if the resistance in that has increased and somehow the displays always feed through that, maybe that would cause it to be dimmer.

So, my next plan, whenever I get around to it, is to take the dash apart and going to see if I can just unplug the on/off light switch to see if I can remove the resistance and see if it goes to full brightness.

[ken729]

According to the schematic diagrams, the only other dimming function thst exists besides the headlght/dimmer switch is what I had mentioned previously: the class 2 data communication dimming function from the BCM. It goes to the radio and instrument panel.

The schmatics also show that in order for headlight/ dimmer switch variable radio & panel dimming to take place , the outside lights must be on ( regardess of control ) . This enables the 12 volt supply voltage to the headlight/dimmmer switch necessary for it to function. In your case, since you have established that the dimming takes place with the outside lights off without being able to vary the dimming further, I believe you can safely rule out the headlight/dimmer switch altogether.

[dorlow]

Originally Posted by ken729

According to the schematic diagrams, the only other dimming function thst exists besides the headlght/dimmer switch is what I had mentioned previously: the class 2 data communication dimming function from the BCM. It goes to the radio and instrument panel.

The schmatics also show that in order for headlight/ dimmer switch variable radio & panel dimming to take place , the outside lights must be on ( regardess of control ) . This enables the 12 volt supply voltage to the headlight/dimmmer switch necessary for it to function. In your case, since you have established that the dimming takes place with the outside lights off without being able to vary the dimming further, I believe you can safely rule out the headlight/dimmer switch altogether.

hmm... Then I have no idea where that leaves me. Kind of frustrating. It isn't a huge issue. Maybe there's no problem and it's all in my head. I'm just so sure it's about half the brightness than when the car was new and it still throws me off because the radio is new and it's the same dimness as the odometer. So, it seems like it has to be something in the car telling them to dim all the time.

[ken729]

Your radio display and odometer should not be so dim during the day that you either have difficulty seeing the digits or notice they are dimmed. I will say however, that after looking at the schematics, it is difficult to see how two separate and independent class 2 communication dimming control circuits ( one for radio, one for odometer) are acting in the same manner. It sounds like a problem with the BCM itself. The next logical first step would be to get it scanned with a Tech 2 for any Body error codes and see if that points you towards a solid solution.

[dorlow]

Originally Posted by ken729

Your radio display and odometer should not be so dim during the day that you either have difficulty seeing the digits or notice they are dimmed. I will say however, that after looking at the schematics, it is difficult to see how two separate and independent class 2 communication dimming control circuits ( one for radio, one for odometer) are acting in the same manner. It sounds like a problem with the BCM itself. The next logical first step would be to get it scanned with a Tech 2 for any Body error codes and see if that points you towards a solid solution.

But doesn't it make sense, even if they're two different circuits, they're tied together somehow. When you twist the headlight knob to dim and brighten the display, the odometer, the lighted dash and radio all get dimmer and brighter at the same time... so they have to be tied together somehow.