Sensitive headlight voltage monitoring

[JPM]

Sensitive headlight voltage monitoring ,I installed a set of driving lights on my truck. Used the high beam's hot wire as a trip for the relay. Now the high beams are resetting, like a circuit breaker. Is the circuit that sensitive? Did I mess something up?

 

[Badunit]

I wouldn't think so. The current to the "trip" side of the relay should draw an insiginificant amount of current as compared to the headlights. I'd check your relay connections and/or check for a short.

 

[JPM]

I was wondering , I bought a cheap relay and maybe its coil draws more than a quality unit like a Hella.

 

[DF5152]

you should be able to get a bosch relay for about 5 buck? sound like something may be wired wrong or a defective relay

 

[CIverson]

I thought these were wired differently than normal. Something like a varying or pulsating signal to tell if the bulb had done out or something.

 

[JPM]

Hi, I unplugged the relay, it still does the same thing. Just now, as I drove home the chime rang and the highbeams momentarily went out and came back on. I wonder if the plug is loose or I did something to mess it up. Maybe a warranty issue with the headlight switch? This was interesting, I was installing the driving lights a couple of days ago,when I checked the plug removed from the headlight bulb with my volt meter it would not show 12 volts just a slight pulse with the highbeams on.

 

[Evan A. Beck]

WHere exactly did you tie into the high beam circuit, and what sort of connection did you use?

 

[JPM]

I used a Scotch-lock, I know ,I don't like them either . I tapped the highbeam wire three inches out of the drivers side socket. Do you think I damaged the wire?

 

[sag2]

The headlamps are not on or off, the FCM pulses the voltage to control them. They call it pulse width modulation. I have the daytime running lights turned on and the FCM controls the pulse width to have the headlamps at about 60% of their output.

 

[Briman]

Sag2, would it be possible to increase the pulse width to improve the headlights?

 

[JPM]

Originally posted by sag2

The headlamps are not on or off, the FCM pulses the voltage to control them. They call it pulse width modulation. I have the daytime running lights turned on and the FCM controls the pulse width to have the headlamps at about 60% of their output.

I'm not sure about that. I probed the highbeam wire as the plug was on the bulb. It read 12 volts, no pulsing. With the plug pulled it pulsed when metered.

 

[sag2]

The only time the headlamps should be less than battery voltage is when you have daytime running lamps. At any other time, the FCM high side driver should have 100% duty cycle, or battery voltage. You probably can not see the pulses with a meter, but would with a lab scope. The meter is usually just too slow to pick it up. There is no fuse on the headlamp circuit. The high side driver in the FCM can sense short to ground, and turn itself off for protection. The lamp outage module senses the resistance in the headlamp circuit, and that might turn on the lamp outage light, but should not cause the headlamps to go off.

If you unplugged the relay from the running lamps, the FCM should just see a standard system. Sounds like you might have a problem in the FCM. An easy way to test the system past the headlamp switch is to disconnect the switch. The headlamps should default to on. If they don't, most likely have FCM or wiring from FCM to lamps problem. If they do, problem is in the switch or the wiring to the instrument cluster, or a bus problem between the cluster and FCM. The headlamp switch is just a variable resister. When the cluster sees a certain voltage from the switch (say 1. 5 volts) it knows you want the headlamps on. The cluster then sends a message over the bus to the FCM that says "he wants the headlamps on". The FCM then powers up the high side driver (an integrated circuit) and sends voltage to the headlight.

Also do not overlook a good ground. Bad grounds can cause all sorts of strange problems.

What ever happened to just turning on a lamp???

 

[JPM]

"What ever happened to just turning on a lamp???"



No s***!

It might have been a pre-existing problem. I just got the truck, I don't think I ran the highbeams that much when we brought it home. I'm going to look it over, remove the Scotchlock and inspect the wire. I used the ground above the drivers side battery, maybe disturbing that caused a problem. Then its off to the dealer.

JPM

 

[JPM]

OK, I removed the ground wires going to the relay . They were under the original wires on the drivers side above the battery. I removed the Scotchlock. The Highbeam wire did not look damaged as far as the wire strands go. So tonight I'll see if I fixed it. I called Geno's by the way ,they are having problems with a "Brite Box" fitted to the 03's+. Imagine that So they are not selling them ,yet.

 

[radar doctor]

Good Article

Sag 2 had a good explanation. . Did i read in the Manual (Not to Tap into the Head Lights)????? What do you think SAG ????

 

[DF5152]

from the manual



FRONT CONTROL MODULE

DESCRIPTION

The Front Control Module (FCM) is a micro con-troller

based module located in the left front corner

of the engine compartment. On this model the inte-grated

power module must be positioned aside in

order to access the front control module. The front

control module mates to the power distribution cen-ter

to form the Integrated Power Module (IPM). The

integrated power module connects directly to the bat-tery

and provides the primary means of circuit pro-tection

and power distribution for all vehicle

electrical systems. The front control module controls

power to some of these vehicle systems electrical and

electromechanical loads based on inputs received

from hard wired switch inputs and data received on

the PCI bus circuit (J1850).

For information on the Integrated Power Mod-ule

Refer to the Power Distribution Section of

the service manual.

OPERATION

As messages are sent over the PCI bus circuit, the

front control module reads these messages and con-trols

power to some of the vehicles electrical systems

by completing the circuit to ground (low side driver)

or completing the circuit to 12 volt power (high side

driver). The following functions are Controlled by

the Front Control Module:

² Headlamp Power with Voltage Regulation

² Windshield Wiper “ON/OFF” Relay Actuation

² Windshield Wiper “HI/LO” Relay Actuation

² Windshield Washer Pump Motor

² Fog Lamp Relay Actuation

² Park Lamp Relay Actuation

² Horn Relay Actuation

The following inputs are Received/Monitored by

the Front Control Module:

² B+ Connection Detection

² Power Ground

² Ambient Temperature Sensing

² Ignition Switch Run

² Washer Fluid Level Switch

² Windshield Wiper Park Switch

² PCI Bus Circuit

I could not find anything in the manual that said not to tap into the light sytem

 

[LRoy]

Anecodotal data point - I have about 20K miles of use (and more night driving then most people do) with a PIAA light setup exactly the way you described. A relay is triggered by the high beam power to automatically bring on the driving lights. No problems at all with this setup.



Leonard

 

[sag2]

It might not say to not tap in, but it would be a good idea not to. A quality relay should not pull much current, but you would not want to hook up a lamp directly.

 

[JPM]

Originally posted by LRoy

Anecodotal data point - I have about 20K miles of use (and more night driving then most people do) with a PIAA light setup exactly the way you described. A relay is triggered by the high beam power to automatically bring on the driving lights. No problems at all with this setup.



Leonard

Leonard, I'm home from work ,tonight I had no highbeam interruptions. I think where I installed the grounds for the driving lights caused a problem, I installed the trip and the power side relay grounds under the factory ground wires above the drivers side battery. I think I should separate the factory and driving light's grounds , maybe the computer sees a ground problem the way I had it. I can't see the Scotchlocked wire causing a problem.

 

[JPM]

OK, Now its been two days, no highbeam disconnects. So I believe it was not a preexisting problem. I'm going reconnect the relay to the highbeam hot wire, , use a different ground path. Has anyone used Silverstars for headlight bulbs? Will they set a code in the computer?