What Does It Mean?
This generic powertrain diagnostic trouble code (DTC) generally applies to many OBD-II vehicles. This may include, but is not limited to, vehicles from Chevrolet, Subaru, Ford, Mazda, BMW, Peugeot, etc.
When a P06B6 code is stored, it means the Powertrain Control Module (PCM) has detected an internal processor performance error with a specific knock sensor circuit (designated 1). Other controllers may also detect an internal PCM performance error (with the knock sensor circuit) and cause a P06B6 to be stored.
The knock sensor is typically screwed directly into the engine block. It is a piezoelectric sensor. The location of the knock sensor varies by manufacturer, but most are found on the sides of the block (between the cylinder liner coolant drain plugs) or in the valley beneath the intake manifold. Knock sensors located on the sides of the engine block are often screwed directly into the engine’s coolant passages. When the engine is hot and the engine cooling system is pressurized, removing these sensors can result in serious burns from hot coolant. Before removing any knock sensor, allow the engine to cool and always dispose of coolant properly.
A piezoelectric sensing crystal is at the heart of the knock sensor. When shaken or vibrated, the piezoelectric crystal produces a small amount of voltage. Since the knock sensor control circuit is normally a single-wire circuit, the voltage generated by vibration is recognized by the PCM as engine noise or vibration. The severity of the vibration encountered by the piezoelectric crystal (inside the knock sensor) determines the level of voltage produced in the circuit.
If the PCM detects a degree of voltage from the knock sensor indicating engine knock or severe spark detonation; it may retard the ignition timing and a knock sensor control code may be recorded.
A very small voltage is always produced by the knock sensor when the engine is running. This is because slight vibration is inevitable, no matter how smoothly the engine runs.
The internal control module monitoring processors are responsible for various controller self-test tasks and the overall responsibility of the internal control module. The knock sensor input and output signals are self-tested and are constantly monitored by the PCM and other associated controllers. The Transmission Control Module (TCM), the Traction Control System Module (TCSM), and other controllers also interact with the knock sensor system.
Whenever the ignition is turned on and the PCM is powered up, self-tests of the knock sensor system are initiated. In addition to performing internal controller self-tests, the Controller Area Network (CAN) also compares the signals from each individual module to ensure each controller is functioning correctly. These tests are performed simultaneously.
If the PCM detects an internal anomaly in the knock sensor processor, a P06B6 code will be recorded and a Malfunction Indicator Lamp (MIL) may be illuminated. Additionally, if the PCM detects a problem between any of the onboard controllers, which would indicate an internal knock sensor system error, a P06B6 code will be recorded and a Malfunction Indicator Lamp (MIL) may be illuminated. Multiple failure cycles may be required for MIL illumination, depending on the perceived severity of the malfunction.
How severe is this DTC?
Internal control module processor codes should be classified as severe. A stored P06B6 code could lead to various driving problems.
What are some of the symptoms of the code?
Symptoms of a P06B6 trouble code may include:
Loud noises from the engine area
Reduced fuel efficiency
A variety of engine driving symptoms
Other stored diagnostic trouble codes
What are some of the common causes of the code?
Causes
of this code may include:
Faulty PCM or PCM programming error
Defective knock sensor
Faulty knock sensor control wiring and/or connectors
A faulty controller power relay or blown fuse
Open or shorted circuit or connectors in the CAN bus
Insufficient control module ground
What are the P06B6 troubleshooting steps?
Even for the most experienced and well-equipped professional technician, diagnosing a P06B6 code can be very challenging. There is also the issue of reprogramming. Without the necessary reprogramming equipment, it will be impossible to replace a faulty controller and perform a successful repair.
If ECM/PCM power codes are present, they will obviously need to be corrected before attempting to diagnose a P06B6.
There are several preliminary tests that can be performed before declaring a controller faulty. A diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable source of vehicle information will be required.
Connect the scanner to the vehicle’s 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 intermittent. After recording all relevant information, clear the codes and test drive the vehicle until the code resets 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 that caused the P06B6 to be stored may even need to worsen before a diagnosis can be made. If the code resets, continue with this short list of preliminary tests.
When trying to diagnose a P06B6, information can be your best tool. Search your vehicle information source for Technical Service Bulletins (TSBs) that match the stored code, the vehicle (year, make, model, and engine), and the symptoms presented. If you find the right TSB, it can provide diagnostic information that will help you significantly.
Use your vehicle information source to obtain connector face views, connector pinout diagrams, component locators, wiring schematics, and diagnostic flowcharts related to the specific code and vehicle.
Use the DVOM to test the controller power fuses and relays. Test and replace blown fuses as needed. Fuses should be tested under load.
If all fuses and relays appear to be functioning as expected, a visual inspection of the wiring and harnesses related to the controller is necessary. You will also want to check the chassis and engine ground junctions. Use your vehicle information source to obtain ground locations for the related circuits. Use the DVOM to test ground integrity.
Visually inspect the system controllers for signs of water, heat, or collision damage. Any damaged controller, especially by water, should be considered faulty.
If the controller power and ground circuits are intact, suspect a faulty controller or a controller programming error. Replacing the controller will require reprogramming. In some cases, you can purchase pre-programmed controllers through aftermarket sources. Other vehicles/controllers will require onboard reprogramming that can only be performed by a dealership or another qualified source.
Unlike most other codes, P06B6 is likely caused by a faulty controller or a controller programming error
Test the system ground integrity by connecting the DVOM’s negative test lead to ground and the positive test lead to battery voltage