P0719 – Torque converter/brake switch B -circuit low

Reinier

By Reinier (Contact Me)
Last Updated 2016-04-04
Automobile Repair Shop Owner

Trouble CodeFault LocationProbable Cause
P0719 Torque converter/brake switch B -circuit low Wiring short to earth, torque converter/brake switch, ECM/PCM!TCM

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What Does Code P0719 Mean?

OBD II fault code P0719 is defined as “Torque Converter/Brake Switch B Circuit Low” (circuit current lower than expected/required], and is set when the Powertrain Control Module detects an abnormal voltage or resistance in the “B” circuit of the brake light switch. The “B” refers to the circuit that controls the brake lamps, which is also the circuit that deactivates the cruise control system (where fitted), and the torque converter lock-up mechanism on vehicles with lockable torque converters.

When the brake controller, such as the ABS system receives a signal from the brake lamp circuit, but the Powertrain Control Module detects a current or resistance that does not correspond to a specified value, code P0719 is stored, and the Check Engine warning light may, or may not be illuminated. The code-setting parameters, as well as the number of fault cycles required to illuminate warning lights may vary from vehicle to vehicle. Data between the various control modules involved in generating, and storing code P0719 is transmitted via the CAN Bus system.

The image below shows the typical location of a brake light switch, which is more often than not the root cause of code P0719 when it fails, or works itself out of optimal adjustment. Note that there are considerable differences in the design, location, operation, and appearance of brake light switches between vehicles.

brake-light-switch

What are the common causes of code P0719 ?

By far the most common cause of code P0719 is the failure, or incorrect adjustment of the brake light switch, which prevents correct functioning of the switch. Other possible causes include-

  • Blown brake light fuse(s)

  • Blown bulb(s)

  • Corroded electrical connectors/wiring/bulb sockets that cause high resistances

  • Short circuited wiring due to wiring chafing, or rubbing against body work

  • Open circuits due to damaged wiring/electrical connectors

  • Poor ground connections

What are the symptoms of code P0719 ?

While the symptoms of code P0719 may vary from vehicle to vehicle, there are some general symptoms that are common to most applications. These symptoms include, but may not necessarily be limited to:

  • 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.

  • Possible illuminated Check Engine (Service Engine Soon) warning light.

  • Other OBD II 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.

How do you troubleshoot code P0719 ?

TIP: Given the fact that bulbs, bulb holders/sockets, and the internal connections in tail light assemblies form part of the “B” circuit, you can save a lot of time and trouble by checking bulb holders/sockets for poor connections due to corrosion first. Repair/replace corroded parts as required.

NOTE #1: It is a common mistake to assume that the torque converter lock-up solenoid has failed, when in fact it is far more likely that the problem involves the brake light switch, electrical wiring/connectors, or even low battery voltages.

NOTE #2: Given the potential of code P0719 to cause crashes, it should never be assumed that the problem has been reliably resolved after making repairs. It is imperative that the system be retested, (and the vehicle is test driven) after each step in the repair procedure to eliminate the possibility of an intermittent fault resurfacing unexpectedly.

NOTE #3: Code P0719 could be accompanied by make and model-specific fault codes, especially body and chassis-related codes, but not always. If no other codes show up, specifically check for “B” (Body), and “C” (Chassis) codes to make sure all bases are covered, since in some applications, “B” and “C” codes, such ABS-related codes for instance, could cause power train issues.

In short, code P0719 means different things in different applications, which means that this code should never be diagnosed and repaired in isolation, so always check for related codes even if none show up automatically.

    • Step 1

Although design specifics vary, the troubleshooting steps below apply to most vehicles, and should serve to diagnose the cause of code P0719 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 also check all relevant fuses, and replace blown fuses as required. Fuses do not necessarily need a reason to blow, so replace blown fuses, clear the code, and test the vehicle to confirm that the system is working. A simple fuse replacement often cures the problem.

    • Step 2

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.

    • Step 3

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.

    • Step 4

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 with regards to color-coding and routing of 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.

    • Step 5

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. PCM failures are relatively rare, but bear in mind that a PCM replacement requires reprogramming.

WARNING: Whatever the actual cause of code P0719 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.

Codes Related to P0719

P0703: Indicates a malfunction in the Torque Converter/Brake Switch B Circuit, which malfunction is related to the absence of a signal, as opposed to a low-voltage signal being present.

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