controller area network (CAN) communication

**jick.cejoco** · December 20th, 2022 05:16 PM

i'm working on a 2020 nissan sentra tijuana special

v.i.n 3N1AB8CV9LYXXXXXX. customer states he replaced the headlight lamps to a higher intensity. the BCM (body control computer) did not recognize the new higher amperage light bulbs. the car lost communication on the CAN protocol. hazard lights, turn signal, third brake light (CHMSL) now inoperative. folks, if you have to replace/customize your car's electrical system, check for safety warnings posted by the manufacturer. terminals 6 and 14 (high and low speed CAN does not have any signal, no communication therefore the turn signal input from the switch is not heard or seen by the bcm. today's cars' switches more often than not, are request inputs and not commands.

**yapoy86** · December 21st, 2022 11:18 AM

Why do they need to make it that complicated noh? It should be just a simple switch eh..

**oj88** · December 21st, 2022 11:26 AM

Likely a blown fuse somewhere? Comms shouldn't stop on account of a wrong bulb. In fact, it should still communicate the problem with the bulb to the other relevant systems. Unless the high-wattage bulb overloaded and popped something which then caused the computer(s) to not receive power.

I agree on the two points raised:

1. Don't change anything unless you've done the research and know exactly what you're doing, and
2. Installing a wrong bulb should just simply pop a fuse and raise a fault condition. It shouldn't kill the computer(s). If it did, it wasn't designed as well to be fault-tolerant. The computers can apparently dish it out, but not take it. lol

**jick.cejoco** · December 21st, 2022 12:14 PM

how i wish it's as simple from the combination switch to the flasher and the lamps. the lights on this car are controlled by transistor drivers inside of the body control computer. the lamps are wired straight to the bcm

**yapoy86** · December 21st, 2022 01:04 PM

Well. That would be a problem.. its just a simple bulb eh to be driven by transistors pa.. like a digital amplifier.. very efficient yet very sensitive in shorts or speaker load.. one wrong connection and its fried chicken

**jick.cejoco** · December 21st, 2022 01:10 PM

Originally Posted by yapoy86

Well. That would be a problem.. its just a simple bulb eh to be driven by transistors pa.. like a digital amplifier.. very efficient yet very sensitive in shorts or speaker load.. one wrong connection and its fried chicken

that's why it's not the time for the untrained "mechanic". things you learned in high school like geometry, chemistry, physics and math are now put to use more on car service procedures. the difference between the "mechanic" and the technician are more pronounced on these newer cars

**oj88** · December 21st, 2022 02:29 PM

They do this to make it modular, universal, and programmable (which does a lot of things we take for granted). This also makes it cheaper for designers to repurpose said modules for other car models.

For example: Instead of discrete circuits for the lights, horn, etc., the lights and horn connects to a module. And then, the light switches and horn button in the cabin connects to another module. There can be dozens of these small modules/controllers inside a car that use the CAN bus to communicate with each other.

This way, everything is software-controlled.... Example use cases: When the ABS/EBD is triggered or heavy braking is applied, it communicates with another module to flash the brake lights or hazard lights. If the airbags/SRS deploys, it sends a similar signal to flash the hazard lights. If the engine is still cold, it tells the transmission to hold the lower gear and retard shifting up.... things of that nature. It's an oversimplification but that's the general idea.

If you had discrete wires for everything and try to emulate the features above, you'll undoubtedly have a mess of wires going everywhere.

**jick.cejoco** · December 21st, 2022 03:05 PM

with the corporate average fuel economy standards, nhtsa and epa standards made things complicated. and to reduce the vehicle weight having miles and mile of wires connecting the control modules, the vehicle control network uses the least amount of wires. some communication protocols are of bluetooth, some fiber optic, some single wire (class 2) and of course the most common high speed CAN. imagine how much wires in the cars now specially if the controller network was non existent