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2002 Impala - No High Beams

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150K views 24 replies 6 participants last post by  clmoffatt  
#1 ·
I've been dealing with this issue for a long time and finally want it resolved. When I click on the high beams, the headlights go dark. I have no high beams. I've checked the bulbs, fuses, etc. Something else is going on. I tried replacing the column "arm switch" but that did not resolve the issue, so I returned the new switch back to the vendor.

I remember years ago (I've had this car a long time) that the Body Control Module (BCM) was changed. I don't remember why this happened but I mention it because after the BCM was swapped, I no longer had my daytime running lights.

Any one have any idea what could be going on?
 
#2 ·
Sounds like you're on the track, as the DRL uses the high beams at a lower power. No DRL, no high beams and vice versa.

Check the wiring at the BCM and see if you can get a logic probe into the connections for the DRL/High beams to verify power to them is leaving the circuit.

When you activate the highs, the lows shut off. This is why your headlights go out when you put on the highs.
 
#3 ·
Well, for years I had no DRLs but did have high-beams. It's only been in the last two years that I no longer have high beams. If I bought a new BCM, I assume I'd have to get it programmed. Is that something that I could do myself.

I really wish I could remember why the BCM was replaced so many years ago.
 
#4 ·
No the BCM is specific to the vehicle and must be programmed using a Tech-II scan tool which is a few grand alone. The BCM only commands the relay up front to switch on the DRL relay and the headlight switch overrides this. One thing to check is the junction block that's part of the fuse panel on the driver side, this is where all the headlight wiring is routed internally and they're known for failures. This part is not easily serviced inside and is best replaced, the 1999-2005 Impala & Monte Carlo part will interchange and I'd look into this before messing with the BCM.
 
#7 ·
Not at all difficult just somewhat tedious with the tangle of wires in that small space. The block in question is bolted to the fuse panel and this is on the driver side behind the access panel. Absolutely make sure you disconnect the negative terminal of the battery before doing anything here as this also supplies raw battery power to the computers.

Do you have the factory wiring diagram for these cars? Trace back the headlight circuits and they will go thru this terminal junction block but also verify the DRL relay in the box under the hood and the connections to make sure they're not burnt. If you have high beams by pulling the lever back this tells me the relay is passing current. No lights at all would point to a failure in the junction block as the headlight grounds pass thru this, I had mine burn the headlight terminals a few years back and this is where I found another example of the GM practice of reaching up their backside orifice to scratch their nose engineering.
Inside this junction block are a number of pressure contact terminals that are sandwiched between two plastic jackfields and this is how they bring everything together. Problem is the internal wiring is barely adequate to handle the current of a common headlight bulb and over time the plastic deforms and melts allowing the internal terminals to fail. The best way to tackle this fault is going backwards from the headlights themselves, thru the DRL relay and following the conductors to their junction points using a multimeter including the ground connections for the lights themselves, +12V power will be on the ORANGE (E8 left headlight) and Dk Blue (E12 right headlight) wire via 15 amp headlight fuse. High Beams are on the PINK wire that junction thru the underhood fuse block then to the Hi/Low dimmer switch which switches the ground between the headlight bulbs passing thru the terminal junction block on the driver side of the dashboard.
Do not confuse the pink wire going to the BCM as a control, this is only a signal input to tell the BCM to illuminate the HIGH BEAM indicator on the instruments, everything at that point is serial digital data with no hard connections between them.
 
#13 ·
I finally got some time to work on my Impala again.

I did a little troubleshooting. I swapped the high beam and low beam bulbs, and low beams still came on and DRLs/high beams did not. I even swapped out the entire headlight assembly with my old one, and that didn't get the high beams working.

I measured the voltages at the left headlight assembly. All measurements are to ground (bolt on the front engine mount).

WIRE COLORHEADLIGHTS OFFLOW BEAM ONHIGH BEAM ON
DK BLUE11.0V10.9V11.0V
PINK11.0V10.8V11.0V
ORANGE11.0V11.0V11.0V
DK BLUE11.0V--11.0V

Before I took the measurements, I had accidentally not reinstalled the DRL relay and took measurements. Those are in the table below (not sure if that is helpful).

WIRE COLORLOW BEAM ONHIGH BEAM ON
DK BLUE----
PINK10.8V10.7V
ORANGE10.8V10.7V
DK BLUE--10.7V

I measured voltages of the DRL relay in the top fuse box under the hood (with the relay removed). All measurements are to ground (the negative terminal on the battery). I think I have the pins labeled correctly.

PINOFFACC ON / HB OFFACC ON / HB ON
C1 (86)12V12V12V
C3 (30)------
D1 (87)12V12V12V
D2 (87a)------
D3 (85)------

I measured voltages of the DRL relay in the top fuse box under the hood (with the relay installed).

PINOFFACC ON / HB OFFACC ON / HB ON
C1 (86)12V12V12V
C3 (30)12V12V12V
D1 (87)12V12V12V
D2 (87a)--12V12V
D3 (85)------

If the ignition is in ACC and I switch the high beams on, I get the dashboard indication that the high beams are on (but again, no actual high beams). If the ignition is off, I do not get the dashboard indication that the high beams are on (not sure if this is the normal behavior).

I went to the junkyard and I salvaged a driver's side fuse block (see attached image). I tried opening it up so I could see its "guts" but I couldn't figure out how to separate the two halves.

Image


Do you think it would be worthwhile to just swap out my fuse block for this one?
 
#8 ·
I learned two things. You're awesome bro.
 
2
#9 ·
Wiring Diagram may be found here - Repair and Diagnosis — 2002 Chevrolet Impala V6-3.4L VIN E Service Manual | Operation CHARM
Looks like there are two possibilities depending on the option code - 6J7 or without 6J7. If you click on expand all at the upper left and do Control F and type in "DRL" you should do a search and find 13 places where "DRL" shows up - if you click on the 9th and 10th of the 13 places you should open up a wiring diagram for the DRL depending on whether your your vehicle has the 6J7 option code.
 
#19 · (Edited)
Well, I swapped out my driver's side fuse block with the junkyard one I got off of an Impala. Still no high beams, no daytime running lights. Could this junkyard fuse block also be faulty? Would it make sense to go salvage another?

Image


Any other troubleshooting steps I could take? I did take some voltage measurements. They're listed elsewhere in this thread.
 
2
#21 ·
I have attached the wiring diagram portions that shows the High Beam circuits and outlined the pink wire that connects from the left headlight to the dimmer switch. If I read your voltage chart correctly the voltage at the pink wire was 12 volts when the high beams were turned on at connection G of the left head lamp. This would indicate to me that connection G is open somewhere between the left headlamp and the dimmer switch as it should be pulled to ground when the high beams are turned on via the dimmer switch. Since the right side high beam (pink wire) does not work either this to me would indicate the wire is open between connection S172 and the dimmer switch part of the multifunction switch. Since the low beams work the dimmer switch appears to be getting a ground from connection G201 and since you state the high beam indicator works the BCM connection at B10 C1 appears to be connecting to ground via the dimmer switch. This to me would indicate an open between S172 and D5. There is also a possibility that the wire is good and a connection right at the dimmer switch has some excessive resistance - enough that the headlight cannot power on by not allowing enough current to flow but enough that the body module sees it close enough to ground level voltage wise to turn on the high beam indicator. I would suggest checking the connection points mentioned with a voltmeter and see what readings you get in relation to ground with the high beams on as this should help you narrow down the problem - hope this helps.
Image
 
2
#24 ·
Here is a copy of the schematic with the circuit portions highlighted that turn on the high beams at reduced intensity when the DRL mode is activated. The BCM connects terminal D3 of the DRL relay to ground causing terminal C3 to connect to terminal D1 of the relay - this connects terminal F of the left high beam headlight to ground at G101. Terminal F of the right side high beam headlight is connected to 12 volts at the EXT LTS fuse (hot at all times). Terminal G of the right high beam headlight is connected to terminal G of the left high beam headlight - this puts the two headlights in a series circuit resulting in each light operating at reduced intensity. Since the DRL do not work either this also may indicate that there is an open connection between the two headlights which is what I would suspect - perhaps at S172. There may be other issues that is not allowing the DRL to function but checking with a voltmeter will probably narrow down where the problem (s) exist. Hope this helps.

Image
 
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