AutoCodes – Buick – P159F Buick

P159F Buick Code - Fuel Economy Mode Switch Circuit Low Voltage

Quick Answer

The Engine Control Module (ECM) supplies 5 V reference voltage, through the 5 V reference voltage circuit, to the S87 fuel economy mode switch. Common causes include Faulty Fuel Economy Mode Switch, Fuel Economy Mode Switch harness is open or shorted, Fuel Economy Mode Switch 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: P159F Buick indicates Fuel Economy Mode Switch Circuit Low Voltage.
Common causes: Common causes include Faulty Fuel Economy Mode Switch, Fuel Economy Mode Switch harness is open or shorted, Fuel Economy Mode Switch 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 1,454

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 Jan 02, 2020

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P159F Buick Description

The Engine Control Module (ECM) supplies 5 V reference voltage, through the 5 V reference voltage circuit, to the S87 fuel economy mode switch. The 5 V reference voltage causes current to flow through a series of resistors in the switch to the switch ground circuit. The ECM monitors the reference voltage through a discrete fuel economy mode switch signal circuit. When the switch button is momentarily pressed, the switch contacts allow the 5 V reference voltage to by-pass one of the resistors. The ECM detects the resulting voltage drop as a fuel economy mode request and sends a GMLAN message to the Transmission Control Module (TCM) indicating the request. When the TCM receives the request, throttle progressions and transmission shift points are modified to optimize fuel efficiency. The Instrument Panel Cluster (IPC) also receives the fuel economy mode request message from the ECM and illuminates the fuel economy mode indicator lamp. The fuel economy mode switch must be pressed for between 0.094-1.5 s to activate the fuel economy mode.

OBDII Code P159F Buick - Fuel Economy Mode Switch Circuit Low Voltage - AutoCodes.com — P159F Buick Code - Fuel Economy Mode Switch Circuit Low Voltage

What does this mean?

What are the Possible Causes of the DTC P159F Buick?

Faulty Fuel Economy Mode Switch
Fuel Economy Mode Switch harness is open or shorted
Fuel Economy Mode Switch circuit poor electrical connection

How to Fix the DTC P159F Buick?

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 P159F Buick 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 P159F Buick code?

Need more information on how to fix the P159F Buick code? Get Access to Factory Service Manuals

Need Help with the Code?

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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 P159F Buick Code

1. What are the common symptoms of OBDII code P159F in a Buick related to the Fuel Economy Mode Switch Circuit Low Voltage?

The common symptoms include poor fuel economy, reduced engine performance, and the vehicle may not enter fuel economy mode.

2. What are the possible causes of OBDII code P159F in a Buick?

Potential causes of this code include a faulty fuel economy mode switch, damaged wiring or connectors in the circuit, or a malfunctioning powertrain control module (PCM).

3. How can I diagnose the Fuel Economy Mode Switch Circuit Low Voltage issue in my Buick?

Diagnosis involves inspecting the fuel economy mode switch, checking for damaged wiring or connectors, and using a diagnostic scanner to read the code and identify the specific problem.

4. Can I drive my Buick with the P159F code present?

While the vehicle may still be operable with this code, it is recommended to address the issue promptly to prevent further damage and ensure optimal fuel efficiency.

5. How can I repair the Fuel Economy Mode Switch Circuit Low Voltage problem in my Buick?

Repair options may include replacing the fuel economy mode switch, repairing or replacing damaged wiring or connectors, and resetting the PCM to clear the code.

6. Will resetting the PCM clear the P159F code in my Buick?

Resetting the PCM may clear the code temporarily, but if the underlying issue causing the code is not addressed, it is likely to reappear.

7. Is the Fuel Economy Mode Switch Circuit Low Voltage problem a common issue in Buick vehicles?

While not extremely common, some Buick models may experience this issue due to the complexity of the fuel economy system.

8. Can a DIY enthusiast fix the P159F code in a Buick?

Depending on their skill level and access to tools, a DIY enthusiast may be able to address this code by following repair guides and being cautious when handling electrical components.

9. Are there any preventative measures to avoid the Fuel Economy Mode Switch Circuit Low Voltage issue in my Buick?

Regular maintenance checks, such as inspecting wiring integrity and ensuring the fuel economy mode switch is functioning properly, can help prevent this issue from occurring.

10. How long does it typically take to repair the P159F code in a Buick?

The repair time can vary depending on the specific cause of the code and the availability of parts, but it may take a few hours to a day to diagnose and fix the issue.