Quote:
Originally Posted by ogakor
I understand the outside/battery temperature and charging issue, but I'm still getting the brake warning light, ABS warning light, and "check brake system" message on some cold weather starts. It happened again this weekend, a few days after my Ford dealer service shop searched for, but was unable to find, any problem or current error code during a 70k service. Outside temperature was 17 degrees. The warnings came on and stayed on upon ignition start. After a minute, I turned the ignition off, waited briefly, then restarted, as was suggested here to reboot the vehicle computer. This time, all three warnings stayed on for about 10 seconds then went off. Hydraulic brakes appeared to function normally, though no regen braking due to the cold. This issue occurs only in cold weather at Lake Tahoe and never in warmer weather off the hill.
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The ABS brake warning and the check brake system message should go out in around 3 seconds after start-up if the system is working properly. When you open the door or the dome light comes on, 12MM of brake fluid is pulled from the master cylinder to pressurize the brake system. After the system is shut down, in 4min the fluid is returned to the master cylinder.
Does anyone think the cold weather may be lowering the volume of brake fluid enough to activate a low brake fluid warning if it is close to needing fluid already? After the fluid is heated and expanded from the pressure pump and engine compartment, some fluid is then returned to the master cylinder to an exceptable level to turn off the warning lights. This would explain no codes and the check brake system and ABS warning lights going out. The manual does say that low fluid would cause a ABS warning. If you have an ABS deactivation, regen braking is also shut down.
Bottom line, try adding a little more brake fluid and post in the morning.
GaryG