P0A94 – DC/DC Converter Performance

By Reinier (Contact Me)
Last Updated 2016-10-09
Automobile Repair Shop Owner

Table of Contents

1. What Does Code P0A94 Mean?
2. What are the common causes of code P0A94?
3. What are the symptoms of code P0A94?
4. How do you troubleshoot code P0A94?
5. Codes Related to P0A94
6. Get Help with P0A94

What Does Code P0A94 Mean?

SPECIAL NOTES: Diagnosing and repairing this code requires professional-grade diagnostic equipment, as well as above average knowledge of hybrid systems in general, and expert-level knowledge of the application being worked on in particular. Therefore, attempting to diagnose and repair this code along with any of its sub-codes is NOT recommended for DIY mechanics or non-dealership technicians who either do not have access to all relevant technical information on hybrid control systems, or who do not possess the required skills and knowledge to diagnose and repair trouble codes related to hybrid propulsion systems successfully.   

Due to both the highly technical and complex nature of hybrid power control systems, and the extremely high voltages (that typically range between 200 to 800 volts to thousands of volts) that  are generated and stored by these systems, there exists a real possibility that serious personal injury or even death can result from incorrect diagnostic/repair procedures. In addition, fire and/or fatal damage to the application’s electrical system could occur.

Also, note that due to the large number of possible causes of code P0A94 and its sub-codes, this guide cannot provide detailed diagnostic/repair information for all, or even most applications. Therefore, the information presented here is for general informational purposes only. Always refer to the relevant manual for the application being worked on for detailed diagnostic and /or repair information, or refer the vehicle for professional diagnosis and repair. END OF SPECIAL NOTES.   

OBD II fault code P0A94 is a generic code that is defined by manufacturers of hybrid vehicles as “DC/DC Converter Performance”, to indicate failures/malfunctions in the electrical side of a hybrid propulsion system. This code is set and a warning light is illuminated when the PCM (Powertrain Control Module) detects an abnormality in the functioning of the DC/DC converter. Note that this code and its various sub-codes relate to both electric vehicles and vehicles with hybrid propulsion systems.

A full description of DC/DC converters and their application in hybrid/electrical vehicles falls outside the scope of this guide, but in simple terms, a DC/DC converter is a device that changes a DC current from one level to another. For instance, on electric vehicles the battery pack voltage is stepped up by several orders of magnitude to provide power for the traction motor that propels the vehicle. However, on some hybrid applications that use internal combustion engines to generate power through a generator, the 12-volt battery current is typically retained to power accessories, and the power from an auxiliary battery pack is stepped up by a DC/DC converter to supply power to the traction motor.

Depending on the design of the system, the DC/DC converter is sometimes used to convert high currents back into lower currents to recharge the battery pack during regenerative braking through complex switching and control circuits. Irrespective of design specifics however, the conversion process to both higher and lower levels requires that some energy be stored temporarily by using various configurations of transformers, super capacitors, and semiconductors, all of which generate enormous quantities of heat during the storage/release process.

To manage this heat, all applications are fitted with dedicated cooling systems that in the case of hybrid vehicles, are entirely separate from the cooling system of the engine. Like the engine cooling system, the cooling systems of electric/hybrid electrical systems use liquid coolant and pumps, radiators and radiator fans, thermostats, heat sensors, and dedicated hoses.

The image below shows a simplified schematic of the layout of the propulsion system components on a typical hybrid vehicle. Note the location of the DC/DC converter relative to other major components.

What are the common causes of code P0A94?

While the basic definition of “DC / DC Converter Performance” is valid for all P0A94 codes, be aware that the meaning of some sub-codes (the three numerals following the main code), may differ between applications. However, the meanings listed below are the most commonly used, but despite this, always refer to the manual for the application being worked on for detailed information.

NOTE: “Service plug” in this context refers to the safety device that must be removed before performing some procedures, “IGCT No. 3 fuse” refers to a particular fuse in the Ignition Circuit of hybrid applications, and “Hybrid vehicle transaxle assembly” often means that replacing the transaxle assembly is the only known cure for that particular sub-code.

Code P0A94-127 – “DC / DC Converter Performance”

• Wiring harness or connector
• Hybrid vehicle transaxle assembly
• Service plug
• Frame wire
• Hybrid battery junction block
• Inverter / converter assembly

Code P0A94-172 – “DC / DC Converter Performance”

• Fuel level
• Engine assembly
• Hybrid vehicle transaxle
• Wiring harness
• Inverter / converter assembly

Code: P0A94-442 – “DC / DC Converter Performance”

• Inverter / converter assembly

Code: P0A94-547 – “DC / DC Converter Performance”

• Wiring harness or connector
• Inverter with converter assembly
• Hybrid vehicle transaxle assembly

Code: P0A94-548 – “DC / DC Converter Performance”

• Inverter with converter assembly

Code: P0A94-549 – “DC / DC Converter Performance”

• Wiring harness or connector
• Inverter with converter assembly
• Hybrid vehicle transaxle assembly

Code: P0A94-550 – “DC / DC Converter Performance”

• Inverter with converter assembly

Code: P0A94-553 – “DC / DC Converter Performance”

• Fuel level
• Engine assembly
• Hybrid vehicle transaxle assembly
• Inverter cooling system
• Cooling fan system
• Wiring harness or connector
• Inverter with converter assembly
• Water pump with motor assembly
• Hybrid vehicle control ECU
• IGCT No. 3 fuse

Code: P0A94-554 – “DC / DC Converter Performance”

• Wiring harness or connector
• Inverter with converter assembly
• Hybrid vehicle transaxle assembly

Code: P0A94-555 – “DC / DC Converter Performance”

• Inverter with converter assembly

Code: P0A94-556 – “DC / DC Converter Performance”

• Wiring harness or connector
• Inverter with converter assembly
• Hybrid vehicle transaxle assembly

Code: P0A94-557 – “DC / DC Converter Performance”

• Fuel level
• Engine assembly
• Hybrid vehicle transaxle assembly
• Inverter cooling system
• Cooling fan system
• Wiring harness or connector
• Inverter with converter assembly
• Water pump with motor assembly
• Hybrid vehicle control ECU
• IGCT No. 3 fuse

Code: P0A94-585 – “DC / DC Converter Performance”

• Inverter with converter assembly

Code: P0A94-587 – “DC / DC Converter Performance”

• Inverter with converter assembly
• Battery smart unit

Code: P0A94-589 – “DC / DC Converter Performance”

• Inverter with converter assembly

Code: P0A94-590 – “DC / DC Converter Performance”

• Inverter with converter assembly

What are the symptoms of code P0A94?

Apart from a stored trouble code and an illuminated warning light, symptoms are mostly make and model specific. Nonetheless, one symptom shared by almost all applications when this code is present is that the vehicle can suddenly shut off when power delivery to the traction motor fails.

Note however that this symptom may manifest in different ways on different applications. Depending on the exact nature of the problem, the vehicle may be immobilized, or it may shut off unexpectedly while traveling, and even then, it may happen only under certain conditions. Consult the manual for the application being worked on for detailed information on possible symptoms of code P0A94.

How do you troubleshoot code P0A94?

WARNING: All applications are equipped with a safety device that needs to be removed before some diagnostic and/or repair procedures can be carried out. These devices work much like isolating switches that when removed, renders the high voltage side of the system safe to work on. Therefore, DO NOT perform any action on a hybrid propulsion system unless you have a full understanding of where this device is located, and how it works. Also, be aware that on most applications, a minimum waiting time of at least five minutes is required for residual current to drain from super capacitors and other devices before the system can be considered safe enough to work on.      

NOTE #1: Almost all manufacturers have assigned additional sub-codes (consisting of three numerals that follow the main code) to this and other codes, to make it easier to trace faults in the propulsion system. One typical example of a sub-code is P0A94–547: while the main definition is still “DC/DC Converter Performance”, the possible causes of this sub-code specifically include failure of the transaxle, which is a relatively common occurrence on some Toyota products. Note however, that sub-codes may not indicate the same sub-system on all applications, and that most generic code readers cannot display the sub-codes. Also, be aware that the “definitions” of sub-codes may differ between applications.

NOTE #2: If you have sufficient confidence in your diagnostic abilities to attempt a diagnosis of this code, DO NOT do so without having access to a repair manual for the application. At a minimum, the manual must include relevant wiring diagrams, comprehensive reference data for purposes of comparing obtained readings to the manufacturer’s specifications, comprehensive information on what exactly each sub-code means for that application, as well as clear, easy to follow diagnostic trees and procedures. If this information is not available, the wisest course of action is to refer the vehicle for professional diagnosis and repair.

NOTE #3: Always observe basic safety procedures when working with high voltages. Always wear suitable gloves, full-face protection to prevent facial burns in case of short circuits occurring, and never use tools that are not properly insulated and rated for their purpose. Be aware that failure to follow these basic rules can result in serious personal injury, or death.  

Step 1

Refer to the “Common Causes” section below.

Step 2

While it may seem that some possible causes are repeated several times for some sub-codes, there is a very good reason for this. Code readers, and in particular cheap generic code readers, cannot pinpoint the exact area in which a fault is present, meaning that if a particular possible cause is listed for more than one sub-code, the root causes of the problem are different from one sub-code to the next. Therefore, from this exhaustive list of possible causes of code P0A94, it should be abundantly clear why uninformed, untrained, or DIY mechanics should NOT attempt a diagnosis and repair of this code, with the possible exception of the DC/DC converter cooling system.

Step 3

Overheating of the converter cooling system is a common cause of P0A94; so if sub-codes 553 and/or 557 are present, the PCM has detected a failure of, or malfunction in the converter/inverter cooling system, which generally does not involve high voltages. If these sub-codes are present, record all codes (and sub-codes) present, as well as all available freeze frame data. This information can be useful if an intermittent fault is diagnosed later on.

Step 4

Since the converter cooling system operates almost exactly like a normal engine cooling system, care must be taken NOT to work on it unless the entire system has cooled down, and the residual pressure in the system has dissipated.

However, do not attempt a diagnosis of the cooling system if you do not have a repair manual (or access to a repair manual) for the application being worked on ready at hand. Also, take a few minutes to read the section on the cooling system carefully as a precaution against both damaging other components/systems, and sustaining personal injury.

Step 5

Once you have a complete understanding of how the cooling system works and know where all its components are located, check the coolant level to verify that the system has not lost coolant. Top off the coolant as required, or make repairs as required to fix coolant leaks.

NOTE: If coolant leaks are found and repaired, be sure the follow the instructions in the manual with regard to filling the system with the correct amount and type of coolant to prevent problems and issues with circulation of the coolant.

Step 6

If the system has not lost coolant, prepare to test the pump and associated sensors. However, since this guide cannot provide detailed repair information for all applications, be sure to follow the instructions in the manual exactly to avoid a misdiagnosis.

Nonetheless, this step will generally involve testing the reference (or input) voltage, ground, resistance, and continuity of all associated components, wiring, fuses, and circuits. Make repairs, or replace components as required to ensure that all electrical values fall within the manufacturer’s specifications.

If the scanner has control functions, command the cooling fan(s) “ON” multiple times to ensure that there are no intermittent faults present that can prevent the fan(s) from operating correctly. Be aware though that as on conventional applications, intermittent faults can sometimes be extremely challenging to find and repair, and in some cases, the fault may have to be allowed to worsen before an accurate diagnosis and definitive repair can be made.

If the scanner cannot control the cooling fan(s), follow the instructions in the manual to test the cooling fan control circuit using a good quality digital multimeter. Compare all obtained readings with those stated in the manual, and make repairs or replace defective components, wiring, sensors, and/or control units to ensure that all electrical values fall within specified ranges.

Step 7

Clear all codes when repairs are complete, and rescan the system to see if the code returns. Note that some applications may require the completion of one or more drive cycles before the code can be cleared.

If the code does not return after several drive cycles, the repair of the converter cooling system can be regarded as having been successful.

Step 8

Apart from the cooling system, there is not much non-professional mechanics can do to diagnose and repair any other sub-codes of P0A94. All other hybrid propulsion related codes require expert level knowledge of the application and its systems; if this knowledge is lacking, refer the vehicle for professional diagnosis and repair.

Codes Related to P0A94

Apart from its sub-codes, there are no known codes related to P0A94.

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