P0AFC Hybrid Battery Sensor Module

OBD-II DTC Datasheet

Hybrid Battery Sensor Module

What does this mean?

This is a generic Diagnostic Trouble Code (DTC) applicable to many OBD-II vehicles (1996 and newer). This may include, but is not limited to, Toyota, Honda, Ford, Subaru, etc. Despite the general nature, the exact repair steps may vary depending on the model year, make, model and transmission configuration.

If your OBD II equipped Hybrid Vehicle (HV) has stored the P0AFC code, it means that the powertrain control module (PCM) has detected a malfunction in the HV battery sensor module. The HV battery sensor module is more commonly referred to as the hybrid vehicle battery control module (HVBCM). This code should only be displayed on hybrid vehicles.

The primary responsibility of the HVBCM (which interacts with the PCM and other controllers) is to monitor and control the high voltage battery pack. Twenty-eight (Nickel-Metal Hydride) battery packs, consisting of eight separate 1.2 V cells in series, constitute the HV battery pack. The high voltage hybrid battery packs are connected in series with bus connectors and high voltage copper cable sections.

Battery temperature, individual cell resistance, battery charge levels, and overall battery health are included among the features monitored and calculated by the HVBMS.

The HVBMS receives input from each individual cell to monitor the individual battery / cell temperature and resistance levels in the battery pack. This information is used to regulate the battery charge rate and the operation of the battery cooling fans (among others). Each individual cell (or battery, depending on the type of system) is equipped with a built-in ammeter / temperature sensor.

If the HVBMS provides an input signal to the PCM indicating a malfunction of the HVBCM (Hybrid Battery Sensor Module), the P0AFC code will be stored and the malfunction indicator lamp may illuminate. Most vehicles will require several failure cycles before the warning light comes on.

Typical Hybrid Battery:

What is the severity of this DTC?

Failure of the Hybrid Battery / HVBCM sensor module (and stored code P0AFC) may result in electrical powertrain shutdown. The P0AFC problem must be resolved urgently.

What are some of the symptoms of the code?

Symptoms of a P0AFC trouble code may include:

Decreased vehicle performance
Reduced fuel efficiency
Other codes related to high voltage battery
Disconnection of the electric motor installation

What are some of the common causes for the code?

Reasons for this code may include:

Defective high voltage battery, cell or battery pack
Loose, broken or corroded busbar connectors or cables
HVBMS sensor malfunction
Controller failure due to programming error

What are some P0AFC troubleshooting steps?

The HV battery system should only be serviced by qualified personnel.

Before attempting to diagnose the P0AFC code, you will need access to the diagnostic scanner, digital volt / ohm meter (DVOM), and HV battery system diagnostic information source.

I like to start my diagnosis by visually inspecting the HV battery and all Controller Area Network (CAN) harnesses. I would focus on signs of corrosion, damage, or other obviously open circuits. Remove corrosion and repair (or replace) faulty circuit as necessary. Before performing any load test on the battery, ensure that the battery pack is free of corrosion problems, that all connections are secure, and that the battery pack is fully charged.

Then connect the scanner to the vehicle's diagnostic socket and retrieve all stored codes and corresponding freeze frame data. Make a note of this information before clearing the codes and test driving the vehicle until the PCM enters ready mode or the code is cleared.

If at this moment the PCM goes into standby mode (codes are not stored); the code is intermittent and can be much more difficult to diagnose.

You may suspect a defective HVBCM / PCM or a controller programming error if all controller power (input) and ground circuits are intact and there is no supply voltage (output) to the sensor from the HVBCM / PCM. Replacing the controller will require reprogramming.

If the HVBCM supply voltage is not present, check all appropriate fuses and relays of the controller power supply. Replace defective components if necessary.

Any controller showing signs of water ingress, heat, or collision should be considered defective.

Although a stored P0AFC code cannot automatically deactivate the HV battery charging system, the conditions that caused the code to be stored may disable it.

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