What does it mean?
OBD II fault code P0724 is a generic code that is defined as “Torque converter/brake switch B -circuit high”, and is set when the PCM (Powertrain Control Module) detects a higher than expected signal voltage from the torque converter/brake switch. Note that on most applications, the torque converter lock-up clutch, and the brake light switch are incorporated into the same switch that is activated when the brake pedal is depressed.
On applications that are fitted with a lock-up torque converter clutch, this clutch locks the engine to the transmission in much the same way that a clutch on a manual transmission forms a positive mechanical link between the engine and the manual transmission. In practice, a lock-up torque converter clutch prevents transmission slippage, which contributes significantly to fuel economy.
However, this clutch is controlled by the TCM (Transmission Control Module) in a way that allows a controlled amount of transmission slippage to occur- both to make gear shifts smoother, and to prevent damage to transmission components when gearshifts take place under hard acceleration.
In terms of operation, the torque converter clutch needs to be released, or disengaged under some circumstances such as when the vehicle decelerates and down shifts take place, or when the vehicle is coming to a stop. If the clutch remained in a locked state, the engine will remain locked to the transmission, which will cause the engine to stall every time the vehicle comes to a stop.
Thus, to disengage the torque converter clutch in a fully functional system, a signal is generated when the brake pedal is depressed, which signal serves as the input signal to disengage the torque converter clutch. When the brake pedal is depressed and a higher than expected input signal passes through the torque converter/brake light switch, the PCM and/or the TCM will recognize the fact as a malfunction, and set code P0724 as a result.
One or both control modules may also illuminate a warning light when the code is set.