98 S10, 2.2L
I have an issue with the DLRs never going off when the key is on. In park, they're on. With parking brake on, they're on. When the low beams are on, it appears the DLRs stay on too, since the entire headlight is lit up.

I've read through the service manual for trouble shooting. If I pull the DLR relay, the lights go out. Plugged in, they come on. The service info says there is a short to ground in the dark green/white wire running between the RH high beam bulb and the under hood fuse box. I've confirmed there is no short to ground in this relative short run of wire which is still protected from point to point it the factory wire loom. I think that this green/white wire is supposed to be a "new" ground for when the DLRs are in use. Ordinarily, (I think) the headlight ground would come from dark blue wires on the RH high and low beams. I'm attaching the schematic I got from the internet for reference. The circuit description has the following to say about how the DLRs work:

During normal operation, current flows to the RT HDLP fuse from the closed contacts of the energized headlamp
power relay. From the RT HDLP fuse, current flows through CKT 198 (DK BLU) to the RH high beam
headlamp to the LH high beam headlamp through CKT 524 (PPL). The normal ground is removed by the
energized headlamp relay. CKT 524 also provides a voltage signal to the BCM in order to confirm proper DRL
operation. The LH high beam headlamp receives a new ground through CKT 711 (DK GRN/WHT) to the
normally open contacts of the daytime running lamp relay through CKT 350 (BLK) to 0102.

When the headlamp switch is in the AUTO or PARK position, the ambient light sensor (located in the right
speaker grill) senses either daylight or darkness and sends the signal to the BCM. When the ambient light sensor
detects a daylight condition, the BCM will activate the following three relays:

• The headlamp power relay
• The headlamp grounding relay
• The daytime running lamp (DRL) relay

The headlamp power relay provides power to the high beam headlamps.

The headlamp grounding relay removes the ground path for regular headlamp operation.

The daytime running lamp (DRL) relay provides a new ground that places both high beam headlamps in a series.

This operation causes the high beam headlamps to operate at half normal output.
The BCM will activate the headlamp power relay by providing power to the relay coil through CKT 352 (WHT)
The relay coil is grounded through terminal F7 connector 2 of the underhood fuse block to CKT 350 (BLK) to
G 102. The BCM will activate the headlamp grounding relay by providing a ground to the coil through CKT 592
(LT GRN/BLK). Power is provided to the coil through CKT 240 (ORN) from the PARK LP fuse. The BCM will
activate the daylight running lamp relay by providing a ground to the coil through CKT 592 (LT GRN/BLK).
Power is provided to the coil by the FOG LP fuse. A voltage signal is sent to the BCM through CKT 524 (PPL)

When I did a continuity test to ground (battery disconnected) on the green/white wire at the LH high beam, I had continuity. I had continuity to ground also on the left low beam yellow/black wire. If I pulled the 10a fuse #15 (coming out of the headlamp relay), I got an open circuit on both wires. I've swapped around the headlamp and dlr relay and got no change.

I'm concluding that something is causing a ground to the green/black wire on the LH high beam and the LH low beam. In looking at the schematic, the obvious culprit would be the headlamp power relay, but unless I've got two relays shorted to the electromagnet coil, I don't see how this can be the cause. The other possible issue I can see would be the diode between the the headlamp ground relay and the DLR relay. That diode runs through the electromagnetic coil of the DLR relay and to where the green/white wire grounds through a black wire at G120. I would think that if it is shorted, it is providing a path to ground that fuse #15 provides when plugged in. I haven't pulled the diode yet. Now that I'm writing this up, it seems to me that it is suspect, but I think I'd need a shorted relay too in order to provide the path to ground with the battery disconnected. Of course, tit could be the BCM too. I don't think it can be a shorted wire anywhere.

Any help would be appreciated.

 

Is this persistent high beam behavior the same in both daylight and at night?


George

 

The sensor will turn on the headlights (and running lights) when it is dark, but the half intensity high beams are on when the low beams are on. So yes the DLRs are on at night and during the day.

 

So then what this boils down to is that you have high beams at night when you are only calling for low beams and that the ambient light sensor is properly detecting the change from light to dark and turning on the headlamps automatically at dark?

George

 

Well, the high beams are on when the low beams are on, but they're at a reduced intensity since their dlrs. I also have the dlrs on at any time the key is on. Whether the transmission is in park or whether the emergency brake is on, the dlrs are on. Obviously, they're not supposed to be. I would like to get the circuit to run properly. I'm just wondering if there's something in the circuit that seems obviously wrong, because I can't figure it out. I think I'm going to try jumping each of the three affected relays one at a time and see what kind of result I get.

 

I just need to fully understand the symptoms so that I can help you. If you call for high beams with the MF switch at night do the regular intensity high beams come on?

George

 

This one has the headlight switch on the dash. When I turn it on, the low beams will come on, but the low intensity high beams(ie, the DLRs) will also stay on. I don't know if the high beams got to full intensity when I pull back the multi function switch on the stalk. I'll give that a check too. Whether you turn on the headlights with the switch or if they turn on automatically, the DLRs remain on. I'll be heading home in a few minutes and I'll double check all the functions and report back. Thanks.

 

OK, as soon as you get me that info we can start tracking down your problem.


George

 

I'm glad I checked because I had it wrong.
The dlrs are on with the key on. When I turn on the headlight switch, the low beams come on and the dlrs go off. When I flick to the high beams, I get full intensity on the high beams and the low beams are off.

I've checked the relays in the headlight ground, headlight power and DLR slots and none of them are stuck closed. The diode tests good.

 

So now please explain what the malfunction is.


George