OBD-II Trouble Code Technical Description
Article by
Stephen Darby
ASE Certified Technician
Internal Control Module Non-Volatile Random Access Memory (NVRAM) Error
What does that mean?
This generic powertrain diagnostic trouble code (DTC) typically applies to many OBD-II vehicles. That may include but is not limited to vehicles from Ford, Mazda, etc.
When a code P06B8 is stored, it means that the powertrain control module (PCM) has detected an internal processor performance error with non-volatile access memory (NVRAM). Other controllers may also detect an internal PCM performance error (with NVRAM) and cause a P06B8 to be stored.
Internal control module monitoring processors are responsible for various controller self-test duties and overall internal control module accountability. NVRAM input and output signals are subject to self-test and are monitored constantly by the PCM and other related controllers. The transmission control module (TCM), traction control module (TCSM), and other controllers also interact with NVRAM.
In automotive applications, NVRAM is used to help retain data memory when power is shut off to the PCM. NVRAM is integrated into the PCM. Even though the NVRAM is capable of more than 1-million programming changes, and is designed to last for hundreds-of-years, it can be sensitive to excessive heat and moisture.
Whenever the ignition is on and the PCM is energized, NVRAM self-tests are initiated. In addition to running internal controller self-tests, the controller area network (CAN) also compares signals from each individual module to ensure that each controller is functioning properly. These tests are performed simultaneously.
If the PCM detects an internal discrepancy in the NVRAM processor, a code P06B8 will be stored and a malfunction indicator lamp (MIL) may be illuminated. Additionally, if the PCM detects a problem between any of the on-board controllers, which would indicate an internal knock sensor system error, a code P06B8 will be stored and a malfunction indicator lamp (MIL) may be illuminated. Multiple failure cycles may be necessary for MIL illumination, depending upon the perceived severity of the malfunction.
Example photo of a PCM:
What is the severity of this DTC?
Internal control module processor codes should be categorized as severe. A stored code P06B8 could result in a variety of drivability concerns.
What are some of the symptoms of the code?
Symptoms of a P06B8 trouble code may include:
- A variety of engine drivability symptoms
- Other stored diagnostic trouble codes
What are some of the common causes of the code?
Causes for this code may include:
- Bad PCM or a PCM programming error
- Open or shorted circuit or connectors in the CAN harness
- Insufficient control module ground
What are some P06B8 troubleshooting steps?
Even to the most experienced and well-equipped professional technician, diagnosing a code P06B8 can prove to be quite a challenge. There is also the issue of reprogramming. Without the necessary reprogramming equipment, it will be impossible to replace a defective controller and complete a successful repair.
If there are ECM/PCM power supply codes present, they will obviously need to be rectified before attempting to diagnose a P06B8.
There are several preliminary tests that can be performed prior to declaring any controller defective. A diagnostic scanner, a digital volt/ohmmeter (DVOM), and a source of reliable vehicle information will be required.
Connect the scanner to the vehicle diagnostic port and retrieve all stored codes and freeze frame data. You will want to write this information down, just in case the code proves to be an intermittent one. After recording all pertinent information, clear the codes and test drive the vehicle until the code is reset or the PCM enters readiness mode. If the PCM enters readiness mode, the code is intermittent and will be more difficult to diagnose. The condition, which caused the P06B8 to be stored, may even need to worsen before a diagnosis can be made. If the code is reset, continue with this short list of preliminary tests.
When attempting to diagnose a P06B8, information may be your greatest tool. Search you vehicle information source for technical service bulletins (TSB) that parallel the code stored, vehicle (year, make, model, and engine), and symptoms exhibited. If you find the right TSB, it may yield diagnostic information that will aid you in a major way.
Use your source of vehicle information to obtain connector face views, connector pin-out charts, component locators, wiring diagrams, and diagnostic flow charts related to the code and vehicle in question.
Use the DVOM to test controller power supply fuses and relays. Test and replace blown fuses as required. Fuses should be tested with the circuit loaded.
If all fuses and relays appear to be functioning as intended, a visual inspection of controller related wiring and harnesses is in order. You will also want to check chassis and engine ground junctions. Use your vehicle information source to obtain ground locations for related circuits. Use the DVOM to test ground integrity.
Visually inspect system controllers for signs of water, heat, or collision damage. Any controller that is damaged, especially by water, should be considered defective.
If controller power and ground circuits are intact, suspect a defective controller or a controller programming error. Controller replacement will require reprogramming. In some cases, you may purchase reprogrammed controllers through aftermarket sources. Other vehicles/controllers will require on-board reprogramming that may only be done through a dealership or other qualified source.
- Unlike most other codes, the P06B8 is likely caused by a defective controller or a controller programming error
- Test system ground integrity by connecting the negative test lead of the DVOM to ground and the positive test lead to battery voltage
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