First, are there any trouble codes if you scan the OBD II system?

Secondly, my thought is that the Headlamp Driver Module (aka Relay 46) is going bad. The part number for this "relay" is GM 15016745.

Good Luck!

 

Crazy ---- I went to Amazon and checked the availability of it for my own 2005 TB/EXT 4.2 and it said it did not fit my vehicle.

I checked up and down the available dates of TBs and then went to a 2005 Silverado and got a "This does not fit this vehicle" and again, I tried up years and down years and still got NO FITMENT.

I tried a 2005 Pontiac Grand Am and got zero.
I tried a 1986 Buick Le Sabre --- up to 2009 and got ZERO there too.

Is that part number really correct?

 

PS --->

I went to the GM Store on Amazon and plugged in "15016745" and got this header....
15016745 4-Pin Headlight A/C Relay Fit for GM Chevrolet Trailblazer Buick GMC Fuse Module Tested Multi-Purpose Relay


Then I clicked on it to order it and got told (again) This does not fit your vehicle - meaning my 2005/TB/EXT 4.2.

Huh?

ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz

 

Well, I have checked it time and time again over the years and it is a "righteous" part number for our platform.

Also, the SMP version, RY560 says it fits 2002 - 2009 TrailBlazers & Envoys, as well as 2005 - 2009 Saab 9-7Xs, 2004 - 2007 Rainiers, 2002 - 2004 Bravadas, and 2003 - 2006 Ascenders.

Now in the online ACDelco parts catalog, it shows that 15016745 is for a 2002 - 2004 TrailBlazer and for 2005 - 2006 TrailBlazers, the part number is 13500114. The 15016745 relay is the solid state high speed switching relay (for PWM purposes) and the 13500114 looks to be a regular relay.

Go figure!

 

Well, I have checked it time and time again over the years and it is a "righteous" part number for our platform.

Also, the SMP version, RY560 says it fits 2002 - 2009 TrailBlazers & Envoys, as well as 2005 - 2009 Saab 9-7Xs, 2004 - 2007 Rainiers, 2002 - 2004 Bravadas, and 2003 - 2006 Ascenders.

Now in the online ACDelco parts catalog, it shows that 15016745 is for a 2002 - 2004 TrailBlazer and for 2005 - 2006 TrailBlazers, the part number is 13500114. The 15016745 relay is the solid state high speed switching relay (for PWM purposes) and the 13500114 looks to be a regular relay.

Go figure!

Thanks because I have a 2002 tb.

Besides swapping the relays with the fan, there a way to test them?

The lights shut off at random at night and if it's the relay I don't want to risk the fan not working lol. If not I'll just buy a new relay this Friday.

 

OK --- I'm still up for a bit --- here's the "Official Amazon Application Chart" in picture form ....

 

DORMAN Part #601-218

 

I'm going to order this unless someone objects.

 

That's just nuts --- OK --- shower time and sleep ...

Byeeeeeeeeeeeeeeeeeeeeeeeeeee

 

Besides swapping the relays with the fan, there a way to test them?

There are issues with testing components for an intermittent failure.

The very instant you remove the part for testing you have altered the conditions under which the failure occurs. So you cannot know if there was trouble with the connection(s) between the part and the vehicle.

And the part can test OK but still fail under different conditions such as temperature. Maybe it fails when hot.

In my read of this thread I have seen no mention of high beam vs low beam.

If I assume the we are speaking of low beam failure I would ask if the high beam lamps work when the low beams fail?

The BCM controls both high and low beam lighting with input signals from the headlamp and multifunction switches. The high beams are powered with a standard electromagnetic relay. The low beams are powered with the HDM, Headlamp Driver Module. This is the PWM device you have been talking about.

The HDM has 12VDC positive power at all times straight through a fuse from the battery. It also has frame ground at all times. The HDM output is wired through separate left and right fuses to the respective headlamp.

The HDM control signal terminal is wired to the BCM. There is a pull-up resistor in the HDM between the 12VDC+ power and the HDM control signal terminal. This can be seen printed on the side of an original equipment HDM.

To activate the low beam lamps at full power the BCM grounds the HDM control signal wire. (this may not be a full true ground but the maximum PWM the BCM is capable of? going by memory here)

When the DRL (daytime running lamp) operation is desired the BCM uses a PWM to ground signal on the control wire to run the lamps at about 80%.

It is my understanding that the DRL does not operate the lamps while the transmission is in Park. And the 2002 model year vehicles (maybe 2003 also?) do not have a "DRL OFF" headlamp switch position like the later models do. Canadian vehicles have the DRL always, they cannot be turned OFF.

There is an ambient light sensor in the center of the dashboard up by the windshield heater vents. This is connected to the BCM and is used for determining the use of the DRL system or the Auto Headlamps function.

With ample daylight sensed and transmission not in "Park" the BCM should engage the DRL lighting, low beams at about 80%.

When the ambient light sensed by this sensor falls below a threshold value the BCM should engage the low beam lamps at maximum power.


Now for the headlamp switch operation.... In the "Auto" position the headlamp switch does not connect anything at all. No control terminal is connected to any other control terminal.

On a 2002 model year there are two input signals from the headlamp switch to the BCM. One is for Park lamps and the other is for Head lamps. These do not switch any operating power at all. These switches operate by grounding control signals from the BCM in similar fashion to what we see in the HDM.

The BCM activates the high beam relay or the HDM (low beam) in accordance to the headlamp switch position and the ambient light sensor value.


So what use is all of this to the issue at hand? Not sure.

If the low beams turn off completely and do not respond to the headlamp switch position shall we guess the HDM is failing?

But what about shifting the transmission to the Park position? That should not make any difference at all to nighttime low beam operation. Only the DRL operation should be affected by the transmission range setting.

Do the low beams come on immediately when the transmission is shifted into Park? Or do they come on when shifted back out of Park?

Is it possible that the ambient light sensor is involved here? Could we be seeing the 80% DRLs at night and not the full brightness low beams?

At night does the "Headlamps ON" indicator turn on like seen here....??

I don't have a clearcut idea here, just throwing out thoughts. I always hold that the best way to fix something is to first learn how the whole business is supposed to work, then go from there

 

There are issues with testing components for an intermittent failure.

The very instant you remove the part for testing you have altered the conditions under which the failure occurs. So you cannot know if there was trouble with the connection(s) between the part and the vehicle.

And the part can test OK but still fail under different conditions such as temperature. Maybe it fails when hot.

In my read of this thread I have seen no mention of high beam vs low beam.

If I assume the we are speaking of low beam failure I would ask if the high beam lamps work when the low beams fail?

The BCM controls both high and low beam lighting with input signals from the headlamp and multifunction switches. The high beams are powered with a standard electromagnetic relay. The low beams are powered with the HDM, Headlamp Driver Module. This is the PWM device you have been talking about.

The HDM has 12VDC positive power at all times straight through a fuse from the battery. It also has frame ground at all times. The HDM output is wired through separate left and right fuses to the respective headlamp.

The HDM control signal terminal is wired to the BCM. There is a pull-up resistor in the HDM between the 12VDC+ power and the HDM control signal terminal. This can be seen printed on the side of an original equipment HDM.

View attachment 62596


To activate the low beam lamps at full power the BCM grounds the HDM control signal wire. (this may not be a full true ground but the maximum PWM the BCM is capable of? going by memory here)

When the DRL (daytime running lamp) operation is desired the BCM uses a PWM to ground signal on the control wire to run the lamps at about 80%.

It is my understanding that the DRL does not operate the lamps while the transmission is in Park. And the 2002 model year vehicles (maybe 2003 also?) do not have a "DRL OFF" headlamp switch position like the later models do. Canadian vehicles have the DRL always, they cannot be turned OFF.

There is an ambient light sensor in the center of the dashboard up by the windshield heater vents. This is connected to the BCM and is used for determining the use of the DRL system or the Auto Headlamps function.

With ample daylight sensed and transmission not in "Park" the BCM should engage the DRL lighting, low beams at about 80%.

When the ambient light sensed by this sensor falls below a threshold value the BCM should engage the low beam lamps at maximum power.


Now for the headlamp switch operation.... In the "Auto" position the headlamp switch does not connect anything at all. No control terminal is connected to any other control terminal.

On a 2002 model year there are two input signals from the headlamp switch to the BCM. One is for Park lamps and the other is for Head lamps. These do not switch any operating power at all. These switches operate by grounding control signals from the BCM in similar fashion to what we see in the HDM.

The BCM activates the high beam relay or the HDM (low beam) in accordance to the headlamp switch position and the ambient light sensor value.


So what use is all of this to the issue at hand? Not sure.

If the low beams turn off completely and do not respond to the headlamp switch position shall we guess the HDM is failing?

But what about shifting the transmission to the Park position? That should not make any difference at all to nighttime low beam operation. Only the DRL operation should be affected by the transmission range setting.

Do the low beams come on immediately when the transmission is shifted into Park? Or do they come on when shifted back out of Park?

Is it possible that the ambient light sensor is involved here? Could we be seeing the 80% DRLs at night and not the full brightness low beams?

At night does the "Headlamps ON" indicator turn on like seen here....??

View attachment 62597



I don't have a clearcut idea here, just throwing out thoughts. I always hold that the best way to fix something is to first learn how the whole business is supposed to work, then go from there

Thank you for the reply. Yes the high beams did work and had to use them to get off the freeway. I had no place to park so I put it in Park and the low beams activated. While on the free way I kept adjusting the switch/knob to turn on the low beams and nothing happened. Don't remember if the green/yellow light was on as I was trying to not cause an accident.

To avoid any overheating issues I think I will buy a new relay from the Parts store. My TB has 228k miles and I don't want her to overheat... Took me a long time to fix that issue already lol.

Also I think you're right about the low beams not producing it's full brightness. I don't drive at night very much but lately I've been and notice the low beams seem weak. I'm going to clean the sensor on the dash right now.

Sorry If I failed to answer all the questions as I'm rushing to the store right now lol. BRB

 

Yes the high beams did work and had to use them to get off the freeway.

So this here tells us the light sensor and the BCM are doing what they are supposed to do. If the light sensor/BCM were not working as they should then the high beam lights would also be affected by the failure. This points the finger of blame at the HDM.

avoid any overheating issues I think I will buy a new relay from the Parts store. My TB has 228k miles

I "think" that the original HDM had some reports of overheating and were upgraded at some point though I am not certain of this. My own 2002 TrailBlazer has somewhere over 292000 miles on it and I have not had any issues with the HDM or cooling fan driver modules. I do have a number of used spares from the Upull yard.

Also I think you're right about the low beams not producing it's full brightness.

Assuming you have the original headlamp shells the lenses are probably quite yellowed. Mine were pretty bad and I used a 3M headlamp lens restoration kit. I spent a good deal of time cleaning them up in 2015 but they are now back to being yellowed again as I did not keep up with the maintenance on them.

Don't remember if the green/yellow light was on as I was trying to not cause an accident.

When that small light is on at the switch it means the headlamps are activated at full brightness. If that indicator is not on then any light seen at the headlamps is the 80% DRL system.

I put it in Park and the low beams activated.

I can think of no explanation for this. Shifting to Park should not normally have any effect that I can explain. Sometimes a bad ground can cause weird symptoms. But a bad BCM ground would cause wide ranging troubles and the low beam headlamps do not share a common ground point.

 

So this here tells us the light sensor and the BCM are doing what they are supposed to do. If the light sensor/BCM were not working as they should then the high beam lights would also be affected by the failure. This points the finger of blame at the HDM.






I "think" that the original HDM had some reports of overheating and were upgraded at some point though I am not certain of this. My own 2002 TrailBlazer has somewhere over 292000 miles on it and I have not had any issues with the HDM or cooling fan driver modules. I do have a number of used spares from the Upull yard.






Assuming you have the original headlamp shells the lenses are probably quite yellowed. Mine were pretty bad and I used a 3M headlamp lens restoration kit. I spent a good deal of time cleaning them up in 2015 but they are now back to being yellowed again as I did not keep up with the maintenance on them.




When that small light is on at the switch it means the headlamps are activated at full brightness. If that indicator is not on then any light seen at the headlamps is the 80% DRL system.






I can think of no explanation for this. Shifting to Park should not normally have any effect that I can explain. Sometimes a bad ground can cause weird symptoms. But a bad BCM ground would cause wide ranging troubles and the low beam headlamps do not share a common ground point.

So I've been driving the tb a bit more at night and been keeping an eye on things including the light on the headlights switch. So far all ok.

No I have aftermarket headlights shells and had them for over a year now.

I think I will order a new relay/hdm. I was reading more post about it and just as you said the hdm is likely the culprit.

 

Regarding the updated "heavy duty" headlamp driver module (13506836), it appears that GM has more or less abandoned it.

It is no longer listed in the online ACDelco parts catalog, and neither Standard Motor Products nor Wells Vehicle Electronics are no longer showing a cross reference for it.

The part is still available on Amazon and rockauto.com only has one in stock.

I guess the over $100 MSRP for the updated relay turned people off.