AutoCodes – Generic – P159F

P159F 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 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 17,739

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

What does this mean?

What are the Possible Causes of the DTC P159F?

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?

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 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 code?

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

Need Help with the Code?

Get the P159F code diagnosed by a professional: Find a repair shop in your area

Information for Specific Makes

P159F Buick — Fuel Economy Mode Switch Circuit Low Voltage
P159F Cadillac — Fuel Economy Mode Switch Circuit Low Voltage
P159F Chevrolet — Fuel Economy Mode Switch Circuit Low Voltage
P159F GMC — Fuel Economy Mode Switch Circuit Low 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 P159F Code

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

- Common symptoms include poor fuel economy, decreased engine performance, and potential issues with the vehicle's Eco mode functionality.

2. What are the possible causes of OBDII code P159F indicating Fuel Economy Mode Switch Circuit Low Voltage?

- The code P159F can be triggered by a faulty fuel economy mode switch, damaged wiring or connectors in the circuit, or issues with the vehicle's PCM (powertrain control module).

3. How can I diagnose the Fuel Economy Mode Switch Circuit Low Voltage issue causing OBDII code P159F?

- Diagnosis typically involves inspecting the fuel economy mode switch, checking the wiring and connectors for damage, and using a diagnostic scanner to read the code and related data.

4. Can a DIY enthusiast repair the OBDII code P159F related to Fuel Economy Mode Switch Circuit Low Voltage?

- While some DIY enthusiasts may be able to address this issue by replacing the fuel economy mode switch or repairing damaged wiring, it is recommended to consult a professional mechanic for accurate diagnosis and repair.

5. Will driving with OBDII code P159F present any risks to the vehicle or its components?

- Continuing to drive with code P159F may result in reduced fuel efficiency and potential strain on the engine due to improper activation of the Eco mode. It is advisable to address the issue promptly.

6. How much does it typically cost to repair OBDII code P159F associated with Fuel Economy Mode Switch Circuit Low Voltage?

- The cost of repairing this code can vary depending on the root cause of the issue, but it may involve expenses for parts replacement, labor charges, and diagnostic fees.

7. Are there any preventive measures to avoid triggering OBDII code P159F related to Fuel Economy Mode Switch Circuit Low Voltage?

- Regularly inspecting the fuel economy mode switch, ensuring proper wiring connections, and promptly addressing any related issues can help prevent the occurrence of code P159F.

8. Can OBDII code P159F be intermittent, or is it typically a persistent issue?

- The code P159F can occur intermittently if the underlying problem with the fuel economy mode switch circuit is sporadic. However, it is essential to address the root cause to prevent further occurrences.

9. Will resetting the vehicle's ECU (engine control unit) clear OBDII code P159F associated with Fuel Economy Mode Switch Circuit Low Voltage?

- Resetting the ECU may temporarily clear the code, but if the underlying issue with the fuel economy mode switch circuit persists, the code is likely to reappear upon driving.

10. Is it safe to drive the vehicle if OBDII code P159F for Fuel Economy Mode Switch Circuit Low Voltage is pending?

- It is generally safe to drive the vehicle with a pending code P159F, but it is recommended to address the issue promptly to prevent potential fuel efficiency and performance issues.