Error Code P06B4 is defined as Sensor Power Supply B Circuit Low. This is a generic trouble code, meaning it applies to all vehicles equipped with the OBD-II system, especially those made since 1996 up to present. This includes vehicle models from but not limited to, Buick, Chevrolet, Chrysler, Fiat, Ford, GMC, Mercedes Benz, etc. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make and model, and powertrain configuration.

Most OBD-II sensors are activated by the signal from the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) or other onboard controllers. The degree of voltage applied (regularly called reference voltage) may vary from low voltage (typically measured in millivolts) up to full battery voltage. The most common voltage for the sensor is 5V, followed closely by battery voltage. However, you need to determine exactly which sensor is related to the code. Thus, you need a reliable source of vehicle information.

When vehicles store the Error Code P06B4, this means the PCM detects a low voltage condition for a specific sensor or ground of sensors. Depending on the manufacturer, the sensor (or sensors) in question, the problem could be related to the exhaust gas recirculation system, heated exhaust oxygen sensor system, automatic transmission, or the transfer case (applicable to all-wheel or four-wheel drive vehicles only). The affected sensor circuit has been given the designation B (A and B may be interchanged as well).

If the PCM (or other onboard controllers) detect voltage lower than expected on power supply circuit, then Error Code P06B4 will be stored, simultaneously activating the Service Engine Soon or Check Engine lamp.

Common Symptoms

  • No start condition for the engine
  • Serious engine drivability problems
  • Engine hesitation, missing, stumbling, or sagging
  • Inoperative transfer case
  • Increase in fuel consumption
  • Erratic or harsh transmission shifting

Possible Causes

The causes for this code include:

  • Blown fuse or fusible link
  • Defective engine, transmission, or transfer case engine
  • Open or shorted wiring/connectors around ground
  • Failed or programming error in the PCM

How to Check

When addressing this code, it’s important to diagnose and repair other related codes first.

As with most codes, you will need a diagnostic scanner, digital volt/ohmmeter (DVOM), and a reliable source for vehicle information to accurately diagnose this code.

Without the means to reprogramming, it can be tricky to diagnose this code accurately. You can, however, search for the TSB (technical service bulletins) that replicates the code, vehicle (year, make, model, and engine), and symptoms for the problem. You can find this information from the vehicle information source.

Then, connect the scanner to the vehicle’s diagnostic port to retrieve all stored codes, including their freeze frame data. Take note of this information in case the problem is proven to be intermittent. Clear the codes then take the vehicle for a test drive. One of the two things can happen; either the code is restored, or the PCM enters readiness mode.

If the code enters readiness mode, then the problem is intermittent. Meaning, you would have to wait for the problem to worsen before you can accurately diagnose it. If the code is restored, however, then you can continue on your diagnosis.

Then, get the face views, connector pinout charts, wiring diagrams, component locators, and diagnostic flow charts of the code for the vehicle in question.

Next, check all related wirings and connectors. Burned, cut, or damaged wirings must be repaired, if not replaced. You can also check chassis and engine grounds and make the necessary repairs. Then, locate the power and ground (use your vehicle information source) to get the ground junction locations for related circuits.

If there are no other codes stored, but the code continues to reset, then test the controller power supply fuses and relays using the DVOM. Replace any blown fuses, fusible links, and relays as necessary. To avoid misdiagnosis, fuses must be tested with the circuit loaded.

If all controller power (input) and ground circuits are intact, and there is no sensor power (output) supply voltage being output from the PCM (or other controllers), then you can suspect a failed or programming error in the PCM. Remember that replacing the PCM requires reprogramming as well. Reprogrammed controllers are usually available through aftermarket sources. Others may require on-board reprogramming, which is available from your dealership or other qualified shops.

Make sure you inspect the system controllers for signs of water damage, heat, or collision damage. Any controllers with signs of damage must be considered defective and must be replaced.

How to Fix

Depending on the diagnosis, common repairs for this code include:

  • Repair or replacement of burnt, or damaged wirings or connectors
  • Repair or defective transfer case
  • Replacement of blown fuses, relays, or fusible links
  • Replacement and reprogramming of PCM

This code is considered severe, since its cope is usually wide, making it difficult to pinpoint precisely how the symptoms has contributed to the code.

The term open could be referred to as disconnected, broken, cut, or unplugged.

Excessive sensor power supply voltage is likely the result of short to battery voltage.