Mike Pyne

Which module is bad or could be effected by high engine compartment temps, Fuse/Relay PCB, BCM, ECM ? When we use a leaf blower and cool down the engine compartment below 90F, the horn works fine again! OBDLINK MX+ DTC: Currently there are (0) none! OBDLINK MX+ DTC Historical Data: (note: the license plate lights and all lights inside/outside the vehicle work!) B3883-01 License Plate Lamp Circuit Short to Battery B3883-04 License Plate Lamp Circuit Open

FYI: I found the information below in a post from member “tbarn”. Low beams are wired direct from bcm. High beam control relay is in the underhood fuse/relay box which are "non-serviceable Printed Circuit Board (PCB) relays and are internal to the block". The headlamps may be turned ON in 3 different ways: •When the headlamp switch is placed in the ON position, for normal operation •When the headlamp switch is placed in the AUTO position, for automatic lamp control •When the headlamp switch is placed in the AUTO position, with the windshield wipers ON in daylight conditions, after a 6 second delay The BCM will also command the low beam headlamps ON during daylight conditions when the following conditions are met: •Headlamp switch in the AUTO position •Windshield wipers ON •Vehicle in any gear but PARK When the BCM commands the low beam headlamps ON, the vehicle operator will notice the interior backlighting for the instrument cluster and the various switches with backlighting control will dim to the level of brightness selected by the instrument panel dimmer switch. The body control module (BCM) monitors three signal circuits from the headlamp switch. When the headlamp switch is in the AUTO position, all three signal circuits are open. When placed in the AUTO position, the BCM monitors inputs from the ambient light sensor to determine if headlamps are required or if daytime running lamps will be activated based on outside lighting conditions. When the headlamp switch is placed in the OFF position, the headlamp switch headlamps OFF signal circuit is grounded, indicating to the BCM that the exterior lamps should be turned OFF. With the headlamp switch in the PARK position, the headlamp switch park lamps ON signal circuit is grounded, indicating that the park lamps have been requested. When the headlamp switch is placed in the HEADLAMP position, both the headlamp switch park lamps ON signal circuit and the headlamp switch headlamps ON signal circuit are grounded. The BCM responds to the inputs by illuminating the park lamps and headlamps. When the low beam headlamps are requested, the BCM applies B+ to both low beam headlamp control circuits illuminating the low beam headlamp.

The horn always work when the vehicle is first started regardless if the outside temp is +100 degrees or not. Horn also works fine in 100+ degree heat while driving the vehicle. However once we stop for a while (15 minutes) and the engine compartment heats up past 110 degrees (Milwaukee infrared gun reading) the horn and only the horn stops working. Everything else works fine, lights, trailer, trailer brake, etc, all good. We replaced both Hi & Lo horns, cleaned & lubed the horn connectors and the 5 large connectors under the fuse/relay block. We read +12.8vdc at the horn. I suspect that the non-replaceable horn relay imbedded on the fuse/relay pcb board may be failing when hot. Or perhaps it is a body control module issue. Any help would be appreciated. Best regards, Mike