AutoCodes – Cadillac – P305B Cadillac

P305B Cadillac 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 Cadillac 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 1,097

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

What does this mean?

What are the Possible Causes of the DTC P305B Cadillac?

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 Cadillac?

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 Cadillac 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.

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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 Cadillac Code

1. What does the OBDII code P305B mean on a Cadillac?

P305B indicates an issue with the DC/DC Converter Ignition On/Start Switch Circuit, specifically that the circuit is experiencing high voltage.

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

Symptoms may include a check engine light, issues with starting the vehicle, reduced electrical system performance, or warning messages related to the hybrid or electrical system.

3. What causes the P305B code to appear on a Cadillac?

The code can be triggered by a faulty DC/DC converter, damaged wiring or connectors in the ignition circuit, a failing ignition switch, or a problem in the vehicle's hybrid or electrical control module.

4. Can a bad battery cause the P305B code?

Yes, a failing 12V battery or improper voltage levels can contribute to this code, as the DC/DC converter relies on proper battery voltage for operation.

5. How do you diagnose the P305B code on a Cadillac?

Diagnosis involves scanning the vehicle with an OBDII tool, checking the DC/DC converter and ignition circuit for proper voltage, inspecting wiring and connectors for damage, and testing the ignition switch.

6. Is it safe to drive with the P305B code on a Cadillac?

It may not be safe, as this issue can affect the vehicleâ€™s electrical systems or starting ability. Itâ€™s recommended to address the problem promptly.

7. How do you fix the P305B code in a Cadillac?

Repairs may include replacing the DC/DC converter, repairing or replacing damaged wiring or connectors, replacing a faulty ignition switch, or reprogramming the control module if necessary.

8. Does the P305B code mean the DC/DC converter is failing?

Not necessarily. While the DC/DC converter could be the problem, the issue could also stem from wiring, connectors, or other circuit components.

9. How much does it cost to fix the P305B code on a Cadillac?

Repair costs vary depending on the exact issue but could range from $200 to $1,500, depending on whether the DC/DC converter or other components need replacement.

10. Can the P305B code be cleared without repairs?

Clearing the code without addressing the underlying issue may result in the code returning. Proper diagnosis and repair are necessary to resolve it permanently.