Error Code P064D is defined as Internal Control Module O2 Sensor Processor Performance Bank 1. This is a generic trouble code, meaning it applies to all vehicles equipped with the OBD-II system. This includes vehicle models from Dodge, Ford, Land Rover, Mazda, etc. Specifications on the definition, troubleshooting, and repairs, of course, vary from make, model, and powertrain configuration.

When Error Code P064D appears, this means the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) has determined a problem in the internal processor oxygen sensor (HO2S) circuit for the engine bank 1. Other controllers may also detect an internal PCM performance error (with HO2S circuit for bank 1) and can cause this code. Bank 1 simple refers to the engine bank that contains the cylinder number 1.

There’s an internal control module monitor that processors responsible for different controller self-test duties and overall internal control module accountability. HO2S input and output signals are subjected to self-test and monitored constantly by the PCM and other related controllers. The TCM (transmission control module) and other controllers also interact with the HO2S.

Every time the ignition is turned on, and the PCM is energized, the self-test for the HO2S will initiate. Aside from running internal controller self-test, the CAN (controller area network) carries serial data from each individual module to make sure the onboard controllers are interfacing correctly. These tests are simultaneously performed.

If the PCM determines an internal discrepancy in the functionality of the HO2S, then it will store the Error Code P064D and activate the Check Engine light. Also, if the PCM sees a problem in any of the onboard controllers, which indicates an internal error in the HO2S, then this code will be stored as well. In some cases, multiple failure cycles may be necessary before the Check Engine light activates. This usually depends on the perceived severity of the malfunction.

Common Symptoms

This code comes with multiple engine drivability and performance symptoms. For one, it causes the engine to experience a lack of power. It also leads to an increase in fuel consumption.

In some cases, other diagnostic codes may be present as well.

Possible Causes

There are many possible causes for this code, such as:

  • Defective HO2S
  • Defective or programming error in the controller
  • Engine exhaust leaks
  • Rich or lean exhaust conditions
  • Blown fuse
  • Bad controller power relay
  • Broken, burnt, chafed, or disconnected connectors and wirings
  • Open or shorted circuit connectors in CAN harness
  • Inadequate ground in control module

How to Check

This code is quite a challenging problem to diagnose, and many times, it involves reprogramming issues. Thus, without the right tools and reprogramming equipment, it will be impossible to replace a defective controller and complete the repair.

If the PCM power supply codes are present, then obviously, they don’t need to be rectified before attempting to diagnose this code.

There are many preliminary tests that can be performed prior to make sure a controller is defective. A diagnostic scanner, DVOM (digital volt/ohmmeter), and reliable vehicle information is needed for the diagnosis of this code.

The first step is to connect the scanner to the vehicle diagnostic port and retrieve all stored codes, including their freeze frame data. You need to write down this information, just in case the problem proves to be intermittent. After writing down all pertinent information, clear the codes and then take the vehicle for a test drive to see if the code resets, or if the PCM enters readiness mode. If the PCM does the latter, then you have an intermittent problem, which is more difficult to diagnose, as it means you would have to wait for the problem to develop more before you can successfully diagnose.

If the code resets, however, then continue with your preliminary diagnosis.

When trying to diagnose this code, refer to your information source or TSB (technical service bulletin); looks for signs and symptoms parallel to the stored code. Search for the year, make, model, and engine of your vehicle. If you are able to find the right TSB, then you may get the best diagnostic information for your problem.

Use vehicle information source to obtain component locations, connector face views, connector pin-out charts, wiring diagram, and diagnostic flow chart related to your vehicle’s error code.

Then, use the DVOM to the test controller power supply fuses and relays. Next, test and replace any blown fuses as necessary. Fuses must be tested with circuit loaded.

If all fuses and relays are running well, check whether the controller related wiring and harness are in order. You may also want to check chassis and engine ground junctions. Again, use your vehicle information source to obtain ground locations as related circuits. Test ground integrity using the DVOM.

Then, check the system controllers for any signs of water, heat, or collision damage. Any controller that is damaged, especially by water, is considered defective and must be replaced.

If controller power and ground circuits are intact, then there’s a good chance the controller is defective, or there’s a programming error in the controller. Thus, controller replacement requires reprogramming. In some cases, you may want to get aftermarket reprogrammed controllers. Some vehicles and controllers require onboard reprogramming that may be done only through the dealership or a qualified shop.

Testing the HO2S

When testing the HO2S, make sure the engine is running efficiently before diagnosing. Problems like throttle position sensor (TPS) codes, ignition misfire codes, mass airflow sensor, and manifold pressure code must be addressed first before trying to diagnose HO2S or lean/rich exhaust codes.

Some manufacturers use a fused circuit to provide voltage for the HO2S. Use the DVOM to test these fuses.

If all other fuses are in good working condition, then find the HO2S for engine bank one. Vehicle must be raised on this process (jacked up or hoist on a secure and safe stand). Once you get access to the suspected sensor, unplug the harness connector and place the key to the ON position. There must be a battery voltage in the HO2S connector. Check with the wiring diagram to establish which circuit is used to supply battery voltage. Check for system ground too.

If both voltage and ground are present, then reconnect the HO2S. Start the engine and then take the vehicle for a test drive. After a drive, let the engine idle (put the transmission in neutral or park). Then, observe the HO2S input data using the scanner. Narrow your scope to the data stream to include only pertinent data for a faster data response. Assuming the engine is running properly, the upstream HO2S should cycle from rich to lean (or vice versa) regularly, with PCM in a closed loop.

How to Fix

  • Replacement of blown fuses
  • Replacement and reprogramming of defective controller
  • Replacement of HO2S
  • Repair or replacement of exhaust leaks
  • Repair or replacement of faulty connectors or wirings
  • Repair or replacement of damaged CAN harness

Defective controller and controller programming error are the two common causes for this code. Connect the negative test lead of the DVOM to ground, and a positive test lead to the battery to test the integrity of the ground system.