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HV-ECU Diagnostic Trouble Codes

HV-ECU Diagnostic Trouble Codes


What are HV-ECU Diagnostic Trouble Codes?

HV ECU stands for Hybrid Vehicle Electronic Control Unit, which is used to administer the hybrid systems, i.e. system that uses gasoline engine with AC electric motor.

HV ECU picks data from sensors to transmit to the vehicles Engine Control Module, or ECM.

An Engine Control Unit (ECU) is a vehicle’s Onboard Diagnostics (OBD) which acts as a notifier for the engine performance and helps minimize the possibility of any unforeseen trouble. Unlike their older models, the modern ECUs process the input parameters from the vehicle’s engine and produce results in real-time using microprocessors. And the language that the ECU uses is the Diagnostic Trouble Codes, where each code stands for specific trouble your car may face. These codes keep the driver informed on the engine’s performance.The HV ECU displays 3-digit “information codes,” along with the letter-plus-4-digit DTC. Such as the DTC, B2799 stands for Immobilizer Malfunction. Meanwhile, the 3-digit code, 101 provides more detailed information that “No input of signal from transponder key ECU.”

Where are ECUs Used?

Modern vehicles such as cars and trucks use ECUs as the engine computer to keep a tab on their performance. They are generally located near the engine of the vehicle; however, their precise location differs from vehicle model to model. Besides the engine, different ECUs are used for different vehicle components, such as AC, traction control, body function, lights, etc.

So it depends on what ECU you’re looking for to determine its placement. For instance, in hybrid systems that employe both the gasoline and AC electric motor, the HV ECUs are located under the carpet on the floor panel, next to the passenger-side instrument panel.

How Do HV-ECU Diagnostic Trouble Codes Work?

The HV-ECU Diagnostic Trouble Codes are warning signs based on a hybrid system vehicle’s engine performance. ECUs display error codes for trouble prevention and optimum security.Whenever a component of your vehicle underperforms, the camshaft and crankshaft sensors, and different ECUs send input to the HV-ECUs where it determines the torque and output power. Other functions that ECUs control are Idle, Variable valve timing (VVT), Fuel injection Emissions systems, and Cruise control. The microprocessor on the HV-ECU’s programmable memory chip receives and processes these inputs. It detects the problem based on the input and determines a Diagnostic Trouble Code representing the problem. These error codes will then be transmitted to your vehicle’s display, warning you about the potential trouble your vehicle may run into. This will help you take preemptive measures in time.

Types of HV-ECUs

  • Engine Control Module: The ECM monitors the fuel consumption and ignition timing using its sensors to obtain the best power and economy out of the engine. 
  • Brake Control Module: The BCM is found in vehicles equipped with ABS (Anti-lock Braking System). It determines when to initiate braking and when to release the brake to prevent the wheels from locking up.
  • Transmission Control Module: When used on an automatic vehicle, the TCM provides smooth shifts by analyzing the engine RPM (Revolutions Per Minute) and acceleration.
  • Telematic Control Module: TCU assures that the vehicle’s onboard services are operational. It manages the vehicle’s satellite navigation, Internet, and phone communication.
  • Suspension Control ModuleThe SCM, which is found in vehicles with active suspension systems, includes optimum ride height and ideal suspension changes based on driving conditions.

Interpreting HV-ECUs DTCs

It can be overwhelming for starters to grasp the concept of DTC codes, let alone remembering each and every one of them. However, learning to interpret these warning codes can come in handy. The latest Onboard Diagnostics system, OBD-II, generates DTCs of up to five characters, with each one providing a specific information about your vehicle. The first one is a letter and tells you about the part of your vehicle with issue.

P (Powertrain)

Engine, fuel system, transmission, and linked accessories.

C (Chassis)

Mechanical systems like steering, suspension, and brakes.

B (Body)

Components found primarily in the region of the passenger compartment.

U (Network)

Vehicle’s onboard computers and related systems.

The second character is a number and represents the status of the code. It’s usually 0, or 1.


Standardized SAE (Society of Automotive Engineers) code.



2 or 3 (rare)

Meaning depends on the letter before. Means Manufacturer specific.

The third character is a number, between 1 and 8, signifying the fault in subsystem.


The fuel or air metering system.


The fuel or air metering injection system.


The ignition system.


The emissions system.


The vehicle’s idle control system and speed controls.


The computer output circuit.

7 and 8

The issue is transmission-related.

You vehicle’s manual or website will explain to you the specific meaning of the last two digits that come together. These two-digit specific fault index numbers lie between 0 and 99.

Common HV-ECU DTCs

There are thousands of warning codes that your car can potentially show you. Here are some of the most common ones:

Essential Hybrid Cars in 2022!

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HV-ECU Diagnostic Trouble Codes


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