Technical Description of OBD-II Trouble Code
The sensor power supply B circuit is experiencing a low voltage condition.
What does that mean?
This is a generic diagnostic trouble code (DTC) that can apply to various OBD-II vehicles (1996-newer), including those from Buick, Chevrolet, Chrysler, Fiat, Ford, GMC, and Mercedes-Benz, among others. The specific repair steps may vary depending on the year, make, model, and powertrain configuration of the vehicle.
When a vehicle equipped with OBD-II has a stored code P06B4, it indicates that the powertrain control module (PCM) has detected a low voltage condition in a particular sensor or group of sensors. The sensor(s) in question may be related to the exhaust gas recirculation system, heated exhaust oxygen sensor system, automatic transmission, or transfer case (for four-wheel drive or all-wheel drive vehicles). The affected sensor circuit is designated as B (A & B may be interchanged as well).
Most OBD-II sensors are activated by a voltage signal provided by the PCM or another on-board controller. The voltage applied, also known as the reference voltage, can range from very low voltage (measured in millivolts) to full battery voltage. The most common sensor voltage signal is 5 volts, followed closely by battery voltage. To determine the specific sensor related to this code, consult a reliable source of vehicle information.
If the PCM or any other on-board controller detects a voltage lower than expected on the power supply circuit designated as B, the code P06B4 may be stored and the service engine soon/malfunction indicator lamp (SES/MIL) may illuminate. Illumination of the SES/MIL may require multiple ignition cycles with a failure.
A typical PCM powertrain control module, opened up:
What is the severity of this DTC?
This code can be categorized as severe. The wide range of sensors involved makes it difficult, if not impossible, to determine the exact severity of the symptoms caused by the condition that led to the storage of the P06B4 code.
What are some of the symptoms of the code?
Symptoms of a P06B4 trouble code may include:
What are some of the common causes of the code?
Possible causes for this code may include:
What are some P06B4 troubleshooting steps?
Prior to diagnosing the stored P06B4 code, address and repair any other sensor-related codes.
To accurately diagnose a code P06B4, you will need a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable source of vehicle information.
If you do not have the means to reprogram controllers, diagnosing the stored P06B4 accurately will be challenging. It may be helpful to search for technical service bulletins (TSB) that match the stored code, vehicle information (year, make, model, and engine), and exhibited symptoms. This information can be found in your vehicle information source. If you find the appropriate TSB, it can provide valuable diagnostic information.
Connect the scanner to the vehicle diagnostic port and retrieve all stored codes and relevant freeze frame data. After recording this information (in case the code is intermittent), clear the codes and test drive the vehicle. One of two outcomes will occur: the code will be restored or the PCM will enter readiness mode.
If the PCM enters readiness mode (indicating an intermittent code), diagnosing the code may be more difficult. The condition that caused the P06B4 to be stored may need to worsen before an accurate diagnosis can be made. However, if the code is restored, continue with the diagnosis.
Obtain connector face views, connector pinout charts, component locators, wiring diagrams, and diagnostic flow charts specific to the code and vehicle in question from your vehicle information source.
Visually inspect all related wiring and connectors. Repair or replace any wiring that is cut, burned, or damaged. It may also be necessary to check chassis and engine grounds and make any necessary repairs before proceeding. Use your vehicle information source to obtain ground junction locations for related circuits.
If no other codes are stored and the P06B4 continues to reset, use the DVOM to test controller power supply fuses and relays. Replace blown fuses, relays, and fusible links as needed. Test fuses with the circuit loaded to avoid misdiagnosis.
If all controller power (input) and ground circuits are intact and there is insufficient sensor power supply voltage output from the PCM or another controller, a defective controller or controller programming error may be suspected. Keep in mind that replacing a controller will require reprogramming. Aftermarket sources may offer reprogrammed controllers for some applications, while other vehicles/controllers may require on-board reprogramming that can only be done through a dealership or qualified source.
Visually inspect system controllers for signs of water, heat, or collision damage. Suspect any controller showing signs of damage to be defective.
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