|Trouble Code||Fault Location||Probable Cause|
|P0724||Torque converter/brake switch B -circuit high||Wiring short to positive, torque converter/brake switch, ECM/PCM!TCM|
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What Does Code P0724 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.
Where is the P0724 sensor located?
On almost all applications, the torque converter/brake light switch is located on the brake pedal, as is shown in the image below.
What are the common causes of code P0724 ?
Some common causes of code P0724 could include the following-
- Blown brake light fuse(s)
- Blown brake light bulb(s)
- Corroded electrical connectors/wiring/bulb sockets that cause high resistances
- Short circuited wiring to battery positive
- Poor ground connections
How expensive is it to fix code P0724 ?
In most cases, an aftermarket replacement torque converter lock-up clutch/brake light switch will cost from around $40 to about $100 if it is replaced on a DIY basis. However, since this switch performs a safety-critical function, it is strongly recommended that only OEM parts be used to repair this code, even though an OEM part may cost up to three times more than an aftermarket unit.
Note that most repair shops will levy a minimum one-hour labor charge to replace this switch, which could add another $100 or so (depending on location) to the repair cost.
What are the symptoms of code P0724 ?
Some common symptoms of code P0724 could include the following-
- Stored trouble code and possibly an illuminated warning light
- Failure of the brake lamps to illuminate
- Brake lamps may be illuminated permanently
- Failure of the lock-up mechanism on the torque converter to engage
- Failure of the torque converter lock-up mechanism to disengage, causing the engine to stall when reducing speed or stopping
- Lock-up mechanism (and/or cruise control) may engage/disengage erratically, intermittently, or unpredictably in some applications
- Other codes relating to the torque converter lock-up mechanism may be present, but be aware that some of these codes may be specific to the make and model being worked on
What are common solutions to code P0724 ?
Common solutions to code P0724 could include the following-
- Testing and replacement of the torque converter lock-up clutch/brake light switch
- Repair or replacement of damaged, shorted, disconnected, or corroded wiring and/or connectors
- Re-adjustment of the torque converter lock-up clutch/brake light switch
How serious is code P0724 ?
Code P0724 should be considered as serious, since severe, if not always fatal damage to transmission components could occur if the fault is not resolved in a timely manner.
How safe is it to still drive the car with code P0724 ?
Vehicles on which code P0724 is present should ideally not be driven, given the facts that stopping distances may be significantly increased, or the engine may stall under braking when the torque converter lock-up clutch does not disengage. This poses an obvious safety risk, especially if the vehicle is driven in heavy traffic.
How difficult is it to repair code P0724 ?
Resolving code P0724 should not present the average non-professional mechanic with undue difficulties, since this code can mostly be resolved simply by replacing the torque converter/brake light switch.
What are the common mistakes when repairing code P0724 ?
The most common mistake made when dealing with this code is condemning and replacing the torque converter lock-up clutch solenoid when the real problem is almost always nothing more serious than a defective brake light switch, incorrect adjustment of the switch, or poor electrical connections at the brake light switch connector.
How do you troubleshoot code P0724 ?
WARNING: Regardless of the actual cause of code P0724 turns out to be, it is recommended that the vehicle not be tested on public roads until it has been determined that the problem is resolved reliably. This code has the potential to cause crashes when brake lights don’t function properly, or worse, the engine stalls unexpectedly because the torque converter remains locked.
NOTE: Although design specifics vary between applications, the troubleshooting steps below apply to most vehicles, and should serve to diagnose the cause of code P0724 on almost any vehicle. Note that you will need a repair manual/wiring diagram for the vehicle being worked on, as well as a high quality digital multimeter capable of both voltage, and Ohm readings.
Assuming that all lamp holders/sockets are free of corrosion, and therefore unlikely to be the cause of the problem, inspect the brake light switch for signs of damage, short-circuiting, or incorrect adjustment. All brake light switches, regardless of manufacture, are of the “On/Off” type, and is usually located on, or near the brake pedal. Incorrect adjustment/setting of the switch can cause it not to close its contacts, thus preventing a signal from being generated.
NOTE: Be sure to check all relevant fuses, but DO NOT replace blown fuses until the reason for the fuse failure had been found and repaired.
If the fault persists, correct the brake light switch adjustment if required, and check the input voltage against the specified value. Also, check the wiring leading out of the switch when the brake pedal is depressed to confirm that the correct current passes through the switch. If the input circuit carries the correct voltage but no current passes through the switch, replace the brake light switch.
If the correct current passes through the switch, inspect all visible and accessible wiring and electrical connectors for signs of damage, burning, short-circuiting, corrosion, or looseness-especially between the brake light switch and Powertrain Control Module. Repair as required, clear the code, test the vehicle, and confirm that the code has not returned.
If the fault persists, disconnect all related control modules, and check all relevant wiring for continuity and/or abnormal resistances. Consult the manual or wiring diagram to determine the color-coding, function, and routing of all associated wiring in order to ensure that the entire circuit is checked and tested. Repair any faults found as required, and recheck all wiring to confirm that all voltage and resistance values fall within specifications. Reconnect all disconnected control modules, clear the code, test the vehicle, and rescan the system to confirm that the fault has not returned.
If the voltage/resistance in all circuits fall within specified values, it is possible that the Powertrain Control Module has failed, and must be replaced. Note though that PCM failure is relatively rare, and bear in mind that a PCM replacement requires reprogramming.
Codes Related to P0724
- P0703 – “Torque Converter/Brake Switch B Circuit Malfunction”
- P0719 – “Torque Converter/Brake Switch B Circuit Low”