AutoCodes – Cadillac – P159F Cadillac

P159F Cadillac 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 Cadillac 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 5,830

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

What does this mean?

What are the Possible Causes of the DTC P159F Cadillac?

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 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 P159F 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.

Need more information about the P159F Cadillac code?

Need more information on how to fix the P159F Cadillac 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 Cadillac Code

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

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

2. What are the potential causes of the OBDII code P159F in a Cadillac?

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

3. How can I diagnose the OBDII code P159F in a Cadillac?

Diagnosis typically involves inspecting the fuel economy mode switch, checking for damaged wiring or connectors, and using a scan tool to communicate with the PCM for further troubleshooting.

4. Is it safe to continue driving with the OBDII code P159F in a Cadillac?

It is generally not recommended to drive with this code present, as it can lead to decreased fuel efficiency and potential engine performance issues. It is best to address the problem promptly.

5. Can I repair the Fuel Economy Mode Switch Circuit Low Voltage issue in my Cadillac myself?

If you have experience with automotive electrical systems and access to the necessary tools, you may be able to repair the issue yourself. However, consulting a professional mechanic is recommended for accurate diagnosis and repair.

6. How much does it typically cost to repair the OBDII code P159F in a Cadillac?

The cost of repair can vary depending on the specific cause of the issue. It may range from a simple fix like replacing a faulty switch or connector to more complex repairs involving the PCM. It is best to get a professional estimate.

7. Are there any temporary fixes I can try for the Fuel Economy Mode Switch Circuit Low Voltage problem in my Cadillac?

Temporary fixes are generally not recommended for OBDII codes, as they may not address the underlying issue and could lead to further complications. It's best to address the problem properly.

8. Will resetting the OBDII code P159F in a Cadillac make it go away permanently?

Resetting the code may temporarily turn off the check engine light, but if the underlying issue is not fixed, the code is likely to reappear. It's important to diagnose and repair the problem to prevent it from coming back.

9. Can the Fuel Economy Mode Switch Circuit Low Voltage issue affect other systems in my Cadillac?

While the primary impact of this issue is on fuel economy and engine performance, unresolved electrical issues can potentially affect other systems in the vehicle. It's best to address the problem promptly.

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

The repair time can vary depending on the exact cause of the issue and the complexity of the repair. It could range from a quick fix to a more involved troubleshooting process. Consulting a mechanic for an estimate is advisable.