P2299

Brake Pedal Pos / Accelerator Pedal Pos Incompatible

Indicator

This code indicates that the PCM (or one of the other supporting control modules) has detected a discrepancy between the accelerator pedal position sensor and the brake pedal sensor or circuit. These control modules may include (but are not limited to) the PCM, the transmission control module, the body control module, the antilock brake control module, the instrument panel control module, the fuel injection control module, the turbo control module, the anti-theft module, the cruise control module, the traction control module, proximity alert module, and the climate control module. Some models initiate a forced idle condition, a forced engine shutdown, or a forced reduction in power, if the PCM recognizes this type of malfunction.

Code Set Parameters

In the event of an accelerator pedal position/brake pedal position discrepancy, a trouble code will be stored and a service engine soon lamp may be illuminated. Some models require multiple drive cycles (as many as 8) with a failure in order for the service engine soon lamp to be illuminated and others will activate it on the initial failure. The brake pedal switch controls brake light activation, cruise control deactivation, and shift interlock functions. If brake lamp circuit voltage is abnormal, the PCM will recognize the failure, store a code, and illuminate the service engine soon light.

Symptoms

Symptoms may include black smoke at startup, poor or no acceleration, a no start condition, misfire at idle, start and stall If this code is stored, and a service engine soon lamp has not yet been illuminated, the code may be shown as a pending code. The cruise control system may fail to engage or disengage when the brake pedal is depressed, the brake lamps (on the rear of the vehicle) may either remain illuminated or fail to illuminate, the shift interlock system may fail to operate properly, or the engine may stall when the brakes are depressed at highway speeds.

Common Causes

The most likely cause of this code being stored is a defective throttle actuator control motor, throttle position actuator, throttle position sensor, or pedal position sensor. Other causes may include corroded, open, or shorted wiring or connectors in the throttle actuator motor or CAN Bus harness, a loose control module ground strap or broken ground wire. This may also be caused by a faulty brake lamp switch or an improperly connected trailer harness. Other possibilities may include open or shorted electrical wiring or connectors, faulty brake lamp bulbs, or faulty bulb sockets in the tail lamp assemblies.

Common Misdiagnosis

Symptoms and stored codes that are present as a reaction to a communication failure are often misdiagnosed and repaired as the cause of the problem. Obviously, this leads to an unsuccessful repair. Engine misfire codes, lean exhaust codes, fuel injector codes, and virtually any other drivability or transmission code that is accompanied by a controller communication code can potentially be a pitfall for misdiagnosis. Follow the rule that says to diagnose codes in the order in which they are stored and you will improve you chances for a successful diagnosis. Utilize freeze frame data to help you determine which codes were stored first. Brake lamp bulbs are often replaced in an unsuccessful attempt to repair this condition. Technicians also report that fuse replacement is only a temporary fix as a faulty brake lamp switch or wiring malfunction is at the root of the problem.

Diagnosis

  • Several tools will be instrumental in attempting to successfully diagnose this code
  • A suitable OBD-II scanner (or code reader), a digital volt/ohmmeter, and a oscilloscope will be most helpful in trying to perform a successful diagnosis
  • A manufacturer’s service manual (or the equivalent) will also be necessary
  • Begin with a visual inspection of all wiring and connectors
  • Repair or replace damaged, disconnected, shorted, or corroded wiring, connectors, and components as necessary
  • Always retest the system after repairs are completed to ensure success. If all system wiring, connectors, and components (Including fuses) appear to be in normal working order, connect the scanner (or code reader) to the diagnostic connector and record all stored codes and freeze frame data
  • This information can be extremely helpful in diagnosing intermittent conditions that may have contributed to this code being stored
  • Continue by clearing the code and operating the vehicle to see if it returns
  • This will help to determine whether or not the malfunction is intermittent. After the codes are cleared, test drive the vehicle to see if the code returns
  • If the code fails to immediately return, you may have an intermittent condition
  • Intermittent conditions can prove to be quite a challenge to diagnose and in extreme cases may have to be allowed to worsen before a correct diagnosis can even be attempted
  • This type of code is only applicable to vehicles with an electronically controlled throttle body
  • These types of systems are often referred to as “drive by wire” throttle bodies
  • A sensor on the accelerator pedal arm inputs a voltage signal to the PCM (or other related controller) which commands the throttle body opened or closed, depending upon conditions
  • Voltage signals from the PCM activate the throttle actuator motor in the direction required by changing voltage levels and polarity
  • As the throttle actuator motor turns, it turns a gear in the throttle body that is meshed with a larger gear
  • This change in ratio allows the throttle plate to be opened quickly and suddenly or slowly and gradually, depending upon the controller’s commands. Begin testing at the throttle position sensor electrical connector
  • Disconnect the connector from the sensor and use the digital volt/ohmmeter to check for voltage and ground signals
  • Typically, a 5-volt reference signal and a battery ground should be present
  • Consult the manufacturer’s service manual for exact wiring diagrams and connector views
  • If no reference voltage and/or ground are detected, disconnect the PCM connector and all related controller connectors and perform a resistance and continuity test on all circuits
  • Repair or replace shorted or open circuits as required
  • Clear codes and test drive the vehicle to ensure that a successful repair has been performed
  • If the voltage and ground signals at the throttle position sensor coincide with the manufacturer’s specifications, use the oscilloscope to monitor pedal sensor operation
  • Look for abnormal spikes in voltage, glitches, or other abnormalities
  • Replace the throttle pedal position sensor as required
  • Clear the codes and test drive the vehicle to ensure that you have completed a successful repair. If the throttle pedal position sensor and related circuits comply with the manufacturer’s specifications, consider that the PCM (or other controller, if applicable) may be defective
  • Controller replacement will require reprograming by a qualified professional
  • Test voltage and ground signals at the throttle actuator control motor connector, when the motor is activated using the scanner
  • If voltage and ground signals are not present, disconnect the connector from the PCM and all related controllers and test individual circuits for resistance and continuity
  • Repair or replace open, shorted, or disconnected circuits as required
  • Clear the codes and test drive the vehicle to ensure a successful repair
  • If voltage and ground signals are present at the throttle actuator motor connector, when activated by the scanner, replace the motor, clear the codes, and drive the vehicle to ensure that your repair has been successful
  • Most automakers do provide service parts for “drive by wire” throttle bodies
  • It is likely that you will need to replace the entire throttle body, which typically includes the actuator motor and the throttle position sensor
  • Pedal sensor replacement may also be recommended with throttle body replacement
  • Consult the vehicle service manual (or equivalent) for the specific manufacturer’s recommendations. The most common type of brake lamp switch is a contact switch that is activated by the movement of the brake pedal mechanism
  • As the pedal is depressed, a push pin in the switch acts as a cam
  • This releases a set of spring loaded contacts, allowing them to touch and complete the circuit
  • Another design utilizes a rocker switch, with a metal plate that moves slightly back and forth as the brake pedal is depressed, to complete the circuit. Typical failures involve worn or broken brake lamp switches in high mileage vehicles
  • After the brake lamp switch is replaced, some models require adjustment
  • If the brake lamp switch is not properly adjusted, a code can possibly be set. Several tools will be instrumental in successfully diagnosing this code
  • A suitable OBD-II scanner (or code reader) and a digital volt/ohmmeter will be most helpful in performing a successful diagnosis
  • Begin with a visual inspection of all wiring and connectors
  • Repair or replace damaged, disconnected, shorted, or corroded wiring, connectors, and components as necessary
  • Always retest the system after repairs are completed to ensure success. If all system wiring, connectors, and components (Including fuses) appear to be in normal working order, connect the scanner (or code reader) to the diagnostic connector and record all stored codes and freeze frame data
  • This information can be extremely helpful in diagnosing intermittent conditions that may have contributed to this code being stored
  • Continue by clearing the code and operating the vehicle to see if it returns
  • This will help to determine whether or not the malfunction is intermittent
  • After the codes are cleared, test drive the vehicle to see if the code returns
  • If the code fails to immediately return, you may have an intermittent condition
  • Intermittent conditions can prove to be quite a challenge to diagnose and in extreme cases may have to be allowed to worsen before a correct diagnosis can be made
  • Continue your diagnosis by depressing the brake pedal with a “dead-man” tool or prybar
  • Move to the rear of the vehicle and observe brake lamp operation
  • If any of the brake lamps are illuminated, you have a brake lamp bulb problem
  • Replace bulbs as required, reset the code, and retest brake lamp operation
  • If no brake lamps are illuminated, check the brake lamp (may be labeled “stop lamps”) fuse and replace as needed
  • If the fuse is blown, reset the code and retest brake lamp operation to see if the fuse blows again
  • If the fuse does not blow immediately, the vehicle may need to be test driven over a period or hours or even days
  • Moisture inside of the tail lamp housings may result in a blown fuse or blown bulb
  • If the fuse immediately blows, you may utilize a short finder to locate shorted or open circuits
  • If a short finder is not available, carefully inspect brake lamp circuit wiring and connectors for signs of damage or corrosion and replace components as required
  • You may also replace the fuse and disconnect sections of the brake lamp switch circuit individually in order to eliminate specific sections and isolate the short
  • Should you find the fuse in good working order, you will want to continue your diagnosis with the brake lamp switch, itself
  • Gain access to the switch, located underneath the driver’s side instrument panel and find the brake lamp switch electrical connector
  • Using the digital volt/ohmmeter, check for input voltage to the brake lamp switch
  • If voltage is detected, depress the brake pedal and check for output voltage from the brake lamp switch
  • If the switch is operating properly from a mechanical standpoint and there is no output voltage signal but there is input voltage, replace the brake lamp switch, reset the code, and retest the system
  • If brake lamps remain illuminated constantly, you may test brake lamp switch operation in a similar manner, only reversed
  • If there is a voltage output signal from the brake lamp switch, but no brake lamps are illuminated, continue your diagnosis by testing for voltage through the turn signal switch
  • If output voltage is present from the turn signal switch, trace system wiring to the rear of the vehicle
  • Use the digital volt/ohmmeter to check continuity in the circuit and replace wiring, connectors, or components as required.