2003 GMC sierra 1500HD with battery drain. Found fuses HVAC/ECAS PCM B and TBC BATT to have amperage draw when engine is off (about 5 amps each). Disconnected alternator....no help. Disconnected all fuses and relays no help. Appears healdight "high beam" idiot light is dimly lit at times....even with engine off. Seem to now have a low idle problem...not sure if its tied together or not. Battery was replaced a few weeks ago.
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Do you have The Automatic or Manual HVAC system ? Doesn't matter fuse's are the same ! Out in the under hood fuse / relay box are two fuse's for heater HVAC BATT fuse #39 10 amp an # 70 40 amp . HVAC BLWR . HVAC = heater ventilation an air conditioning ! So Tom what problem are you having ? Heater fan not working ? There is also a blower motor control module involved !
You can start by trying an actuator recalication.(w/o scan tool)
1. clear all DTCs by disconnecting the battery.
2. remove the HVAC/ECAS fuse for a minmum of 10 seconds.
3. install the HVAC/ECAS fuse.
4. start the vehicle.
5. Wait 40 seconds for the HVAC control module to self-calibrate.
If this doesnot work, probably the right actuator is defective. You
will have to replace it. In the center of the HVAC module, there are two actuators, one is on the top part of the module and the other one is Under. The right actuator is the top one.
cud--but test alternator and make sure batt is holden 12.6v at all times--also inspect wiring and chec fuses and maxi fuses under hood--with older cars components wear and gain resistence too causing blacout until vehicle cools down
This fuse is for the body control module, so your draw is probably something controled by the bcm. Get a manusl, get a list, and eliminate them one by one until your draw is gone! Good luck, let me know if you need any more help!
what fuses were blown and replaced? Theres a TBC fuse under the hood, along with a Headlamp Relay. Theres a R HDLP and LT HDLP fuses, make sure they are getting power, and are good. If the LT HDLP and RT HDLP fuses are good AND getting power, then the TBC fuse and the relay is good. then I would suspect the Hi-Lo dimmer switch bad. The LOW beam ground wire is YELLOW, the high beam ground is PURPLE. see if high beams work, if they do, then I suspect the dimmer switch is bad.