AutoCodes – Generic – P0AF9

P0AF9 Code - Hybrid Battery System Voltage Unstable

Quick Answer

The Engine Control Module (ECM) monitors the correlation of the generator battery disconnect control module battery voltage and the Starter Generator Control Module (SGCM) output voltage to detect a 36 volt cable open or fuse/relay failure. Common causes include 36 volt battery cable open, Hybrid Battery Pack fuse open, Hybrid Battery Pack contactor open. 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: P0AF9 indicates Hybrid Battery System Voltage Unstable.
Common causes: Common causes include 36 volt battery cable open, Hybrid Battery Pack fuse open, Hybrid Battery Pack contactor open.
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 2,052

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 11, 2019

Description
Possible Causes
How To Fix
Cost to Diagnose
Comments
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Code P0AF9 Description

The Engine Control Module (ECM) monitors the correlation of the generator battery disconnect control module battery voltage and the Starter Generator Control Module (SGCM) output voltage to detect a 36 volt cable open or fuse/relay failure. The ECM also monitors to detect an over voltage condition and protect the MOSFET (load dump). If either one of these conditions is detected, the appropriate Diagnostic Trouble Code (DTC) will set.

OBDII Code P0AF9 - Hybrid Battery System Voltage Unstable - AutoCodes.com — P0AF9 Code - Hybrid Battery System Voltage Unstable

What does this mean?

What are the Possible Causes of the DTC P0AF9?

36 volt battery cable open
Hybrid Battery Pack fuse open
Hybrid Battery Pack contactor open
Hybrid Battery Pack ground cable or connection

How to Fix the DTC P0AF9?

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 P0AF9 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 P0AF9 code?

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Information for Specific Makes

P0AF9 Chevrolet — Hybrid Battery System Voltage Unstable
P0AF9 GMC — Hybrid Battery System Voltage Unstable
P0AF9 Saturn — Hybrid Battery System Voltage Unstable

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.