What does it mean?
Because this is a B2xxx code, this means it is manufacturer-defined, so your vehicle’s actual failure may not be related to this definition. The body controller includes everything not controlled by the engine, transmission, and chassis controllers, such as the headlamps, power windows, and air conditioning system. In this case, we’re looking at the headlamp control system, which typically includes the headlamps and taillamps, headlamp controller, headlamp switches, and light sensors.
If the headlamps or stuck on or off, you may have a problem with the headlamp mode control circuit. The typical headlamp control stalk might include the headlight switch, headlamp mode switch, flash-to-pass switch, foglamp switch, and turn signal switches. After the headlamps have been turned on, using the headlamp switch, the headlamp mode select switch switches between low beams and high beams.
If the body control module (BCM) detects a fault in the headlamp mode select switch or circuit, it will set a DTC (diagnostic trouble code) in memory. For some vehicles, DTC B2586 is defined as “Headlamp Mode Select Circuit Failure.”
Symptoms
- High beams cannot be switched on, or will not switch back to low beam
- Headlamps stay stuck on high, which draws headlight flashes from oncoming traffic
- Flash-to-pass does not work, or works while the normal high beam position does not
- High beam indicator in the cluster lights up while the lamps do not change, or stays on constantly
- Beam function changes when the stalk is jiggled
- Headlamps stay on or refuse to come on at all in some switch positions
Likely causes
- Worn or burnt contacts inside the multifunction stalk that carries the beam select switch
- Liquid spilled into the steering column stalk, or moisture that has crept in and corroded the contacts
- Open or shorted wire between the stalk and the BCM, often at the column connector
- Loose, corroded or pushed-back terminal at the multifunction switch connector
- Damage to the wiring or connector after steering column, airbag or clockspring work
- BCM input circuit fault or a module that has lost its configuration
- Aftermarket lighting or a beam conversion wired into the mode select circuit
How to fix it
- Try each stalk position and note exactly which functions work, since the pattern narrows the fault to switch, wiring or module
- Read the beam select switch state in live data while operating the stalk and see whether the module registers the change
- Unplug the multifunction switch connector and check the pins for corrosion, discolouration and backed-out terminals
- Test the switch itself for continuity in each position and replace it if the contacts are erratic
- Check the wires between the stalk connector and the BCM for opens and shorts to ground or power
- Remove any aftermarket lighting wiring tied into the beam circuit and retest with factory wiring
- Only after the switch and wiring are proven good should the BCM be evaluated or its configuration checked