|Trouble Code||Fault Location||Probable Cause|
|B2586||Headlamp Mode Select Circuit Failure|
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What Does Code B2586 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.
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.”
What are the common causes of code B2586?
Depending on year, make, and model, DTC B2586 may have number of causes. Here are some of the most common.
Ford – On Ford Windstar and other models, fuse #10 feeds a number of systems, including the headlamps, air conditioning, and anti-lock brake system, to name a few. In some cases, over a dozen DTCs may be set in these systems, all traced to a single blown fuse. In the case of this vehicle, the blown fuse was caused by brake fluid entry into the brake fluid pressure sensor, causing a short circuit. The sensor may require replacement, but some have noted simply cleaning out the connector was enough to eliminate the short circuit. Of course, make sure you fix the source of the leak before it causes the same problem again in the future.
What are the symptoms of code B2586?
You will probably not experience any drivability symptoms with this fault (see common causes below for exception). With a mode control circuit failure, though, you may not be able to control the high-beams or low-beams. Depending on the nature of the failure, the headlights may or may not turn on, or the high-beams may not turn on or off.
How do you troubleshoot code B2586?
As far as I can tell, Ford and Chrysler products use this definition, including Ford, Mazda, Chrysler, Plymouth, Jeep, Fiat, and perhaps others. You may need to check with your dealer to be sure before proceeding with troubleshooting. Regarding troubleshooting the Headlamp Mode Select Circuit, you will need an EWD and DMM (electrical wiring diagram and digital multimeter) to continue diagnosis.
Check all fuses and connectors related to the headlight control system. Repair short circuits, which cause blown fuses, then replace fuses. Never replace a fuse with a higher-rated one, that is, don’t replace a 10 A fuse with a 20 A fuse, as you could possibly ruin the circuit that the fuse is designed to protect. A blown fuse means there is a problem with the circuit, not with the fuse.
Make sure that all connectors are firmly seated and there are no bent or broken pins, corrosion, or evidence of water entry. Repair as needed.
Swap the headlamp high-beam relay for a known-good relay, such as from the low-beams. If the high-beams now work properly, replace the defective relay. Of course, make sure you mark the relays’ original locations so you don’t accidentally disable some other system!
Test the headlamp mode select switch. Using the EWD and DMM, check for inputs and outputs to the mode select switch. These may be continuity or resistance checks, depending on the vehicle. If the switch fails these checks, then you might need to replace the mode select switch.
Codes Related to B2586
B1470 Lamp Headlamp Input Circuit Failure
B2472 Fog Lamp Switch Failure
B2501 LF Lamp Low Beam Circuit Failure
B2503 RF Lamp Low Beam Circuit Failure
B2598 Headlamp Relay Circuit Failure