AutoCodes – Generic – P305B

P305B Code - DC/DC Converter Ignition On/Start Switch Circuit High Voltage

Quick Answer

The Body Control Module (BCM) controls the ignition main relay through the control circuit by applying voltage to the circuit. Common causes include Faulty Power Supply Transformer, Power Supply Transformer harness is open or shorted, Power Supply Transformer circuit poor electrical connection. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means: P305B indicates DC/DC Converter Ignition On/Start Switch Circuit High Voltage.
Common causes: Common causes include Faulty Power Supply Transformer, Power Supply Transformer harness is open or shorted, Power Supply Transformer circuit poor electrical connection.
Severity: High - diagnose this code as soon as possible.
Can I drive?: Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

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Code Popularity 5,081

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on May 16, 2019

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P305B Description

The Body Control Module (BCM) controls the ignition main relay through the control circuit by applying voltage to the circuit. The power supply transformer samples the system voltage on the Ignition 1 voltage circuit from the ignition main relay. If the Power Supply Transformer detects a fault in the circuit it will request the Engine Control Module (ECM) to set the Diagnostic Trouble Code (DTC) and illuminate the Malfunction Indicator Light/Lamp (MIL).

OBDII Code P305B - DC/DC Converter Ignition On/Start Switch Circuit High Voltage - AutoCodes.com — P305B Code - DC/DC Converter Ignition On/Start Switch Circuit High Voltage

What does this mean?

What are the Possible Causes of the DTC P305B?

Faulty Power Supply Transformer
Power Supply Transformer harness is open or shorted
Power Supply Transformer circuit poor electrical connection

How to Fix the DTC P305B?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P305B code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

Need more information about the P305B code?

Need more information on how to fix the P305B code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the P305B code diagnosed by a professional: Find a repair shop in your area

Information for Specific Makes

P305B Buick — DC/DC Converter Ignition On/Start Switch Circuit High Voltage
P305B Cadillac — DC/DC Converter Ignition On/Start Switch Circuit High Voltage
P305B Chevrolet — DC/DC Converter Ignition On/Start Switch Circuit High Voltage
P305B GMC — DC/DC Converter Ignition On/Start Switch Circuit High Voltage

About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about P305B Code

1. What does the OBDII code P305B mean?

P305B indicates a high voltage issue in the DC/DC converter ignition on/start switch circuit, which is part of the vehicleâ€™s electrical system responsible for regulating voltage.

2. What are the common symptoms of a P305B code?

Symptoms may include difficulty starting the vehicle, illuminated check engine light, electrical system malfunctions, and potential battery charging issues.

3. What causes the P305B code to appear?

Common causes include damaged wiring or connectors in the DC/DC converter circuit, a faulty DC/DC converter, a failing ignition switch, or a malfunctioning powertrain control module (PCM).

4. Can I drive my car with a P305B code?

Driving with this code is not recommended, as voltage irregularities can lead to further electrical or starting system issues and may leave you stranded.

5. How do I diagnose a P305B code?

Start by inspecting the wiring and connectors in the DC/DC converter circuit for damage or corrosion. Then test the DC/DC converter, ignition switch, and related components using a multimeter.

6. How can I fix the P305B code?

Repairs may involve replacing damaged wiring, repairing corroded connectors, replacing the DC/DC converter, or addressing issues with the ignition switch or PCM.

7. Is the P305B code related to the hybrid or electric vehicle system?

Yes, this code is commonly associated with vehicles equipped with hybrid or electric systems where a DC/DC converter plays a critical role in managing voltage for the 12V system.

8. What tools are needed to troubleshoot a P305B code?

Youâ€™ll need an OBDII scanner, a multimeter for testing voltage and continuity, and possibly a wiring diagram for your vehicleâ€™s DC/DC converter circuit.

9. Can a weak battery cause the P305B code?

A weak or failing battery may contribute to voltage irregularities, but it is more likely caused by issues directly within the DC/DC converter circuit.

10. How much does it cost to fix the P305B code?

Repair costs can vary widely depending on the root cause, ranging from $100 for minor wiring repairs to over $1,000 if the DC/DC converter or ignition switch needs replacement.