Agent$mith

iTrader: (2)

2001 Lexus GS300
During the last few days my battery light would come on and off during my drive. It would come on when I revved the engine to 2k RPM and then come off when I took my foot off the gas. I decided to check the battery connections and alternator as well. I saw a video on YouTube on how to check with a multimeter at VDC and followed it. It all looked good according to the range they said. I got:
12.6v resting
14.7v when engine on revved to 2K RPM
14.10v when engine on loaded with rear defroster and headlights on and revved to 2K RPM

Then checking voltage drop test:
.01 when I touch negative on battery to alternator casing revved to 2K RPM
.2 when I touched positive on battery to B+ post of the alternator revved to 2K RPM

After removing the cables and cleaning them before these tests, the battery light stayed on and Autozone confirmed both the battery and alternator were good. Also my DRLs stopped working, but the high beams worked when turn on. The hand brake is not engaged either. I checked both the DRL 1 and 2 fuses below the battery and they are good. I saw the Dimmer DRL No.2 relay and the DRL relay behind the driver headlight. I unplugged the left side of the module by itself and both high beams would be dim and then unplugged the right side by itself and the high beam on the driver side would only work.

Been searching the forums and IS forums and no luck. Can someone please help me? Running out of ideas before going to a mechanic and trying to save some money.

Bhubb18

iirc DRL is just high beam run at 6V, just in case you didn't know. Whats battery voltage at idle?

Agent$mith

iTrader: (2)

I know DRL are just high beam run at 6V. The high beams work when turned on, but when the car starts or drives, the drl mode doesn't turn on at all anymore. I'm thinking it has to be a relay or switch, but not sure.

The battery voltage is 12.6v when resting, idle when the engine is off.

lyonkster

You might want to check that the DRL load resistor has not burned out. I think if it was burned out (open circuit to ground), you would not have DRL's but will still have high beams.

Agent$mith

iTrader: (2)

Leon,
I think you are on to something. I just went out to look at the resistor and touched it with the car on and it's cold, not hot at all. How long should it take to be hot if working since there is a warning message about it being hot? I'm hoping the resistor is causing my battery light to be on too, positive thinking so I knock two birds with one stone.

lyonkster

Well I hope so, but I'm not sure this is telling you enough yet. The fact that the resistor is cold only means that there is no current flowing through it, it doesn't tell you if current is being supplied to the resistor but the resistor is open-circuit, or if current is not being supplied to the resistor due to an upstream problem. Check for voltage at the resistor, that will tell you if it's the resistor or something upstream.

Agent$mith

iTrader: (2)

Leon. I just checked the continuity at the socket and it looked good. I'm a newbie at checking voltage at plugs and not sure how to do that though.

lyonkster

Check if you are getting 12V at the wire coming to the resistor, red with blue stripe.

Agent$mith

iTrader: (2)

With the car on, I turned the multi meter to VDC 20 and pushed the red pin into the side of the socket with the red and blue stripe and let the black pin touch bare metal and got 0 as a reading. :/

lyonkster

Well that rules out the resistor, since it's not even getting power. Let's start from the supply end then - are you getting 12V at the DRL NO. 2 fuse output, red wire with white stripe?

Better yet, follow this description of DRL operation and see how far the 12V signal is getting in the "The current flows from the battery..." description:

lyonkster

Just to confirm, when you say "with the car on", it has to be engine running, and parking brake off - did you do that?

Agent$mith

iTrader: (2)

With the car on, the wires showed 0, but when I turned on the highbeams, the red/blue read 14.34v and the red/white stripe read 8.88v on the wire plugging into the left part of the drl relay harness on the driver side of the vehicle. Not sure if that was what you meant. Thanks.

lyonkster

DRL's only work with the parking brake off and the engine running. So I just wanted to make sure you are getting 0V at resistor with the engine running and parking brake off. The high beams bypass the resistor, so that's a different part of the circuit.

Agent$mith

iTrader: (2)

Leon. I had the car engine on with the parking brake off. I checked the flow of current by the pic and got power at the drl no. 2 fuse, but no power at the H-LP L UPR fuse. I was thinking it was the drl no. 2 relay and bought a new one, but no success. I'm debating if it's the drl module or the drl relay with the two wire harness plugs behind the driver's side headlight. I checked the power at both plugs and got 0 volts. What do you think? Thanks for the pic and patience.

lyonkster

OK, go to the Dimmer DRL NO 2 Relay (the one you just replaced?) and check to see if you are getting12V at the coil side, the red wire with yellow stripe. That'll tell you if the coil is energizing the relay. If it's not, you probably will have to look at the Main DRL Relay.