AutoCodes – Mercury – P1780 Mercury

P1780 Mercury Code - Transmission Control Switch Circuit is Out of Self-Test Range

Quick Answer

The Transmission Control Switch (TCS) is a momentary contact switch that is located on the end of the transmission control selector lever. Common causes include Transmission Control Switch (TCS) not cycled during the self-test, Faulty Transmission Control Switch, Transmission Control Switch harness is open or shorted. 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: P1780 Mercury indicates Transmission Control Switch Circuit is Out of Self-Test Range.
Common causes: Common causes include Transmission Control Switch (TCS) not cycled during the self-test, Faulty Transmission Control Switch, Transmission Control Switch harness is open or shorted.
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 3,783

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 Aug 01, 2020

Description
Step-by-Step Diagnostic Guide
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P1780 Mercury Description

The Transmission Control Switch (TCS) is a momentary contact switch that is located on the end of the transmission control selector lever. Pushing the TCS will either disengage or engage the overdrive function of the transmission. During Key ON Engine Running (KOER) self-test the TCS must be cycled, the Diagnostic Trouble Code (DTC) will set anytime Powertrain Control Module (PCM) detects a TCS out of self-test range.

OBDII Code P1780 Mercury - Transmission Control Switch Circuit is Out of Self-Test Range - AutoCodes.com — P1780 Mercury Code - Transmission Control Switch Circuit is Out of Self-Test Range

What does this mean?

What are the Possible Causes of the DTC P1780 Mercury?

Transmission Control Switch (TCS) not cycled during the self-test
Faulty Transmission Control Switch
Transmission Control Switch harness is open or shorted
Transmission Control Switch circuit poor electrical connection

How to Fix the DTC P1780 Mercury?

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 P1780 Mercury 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 P1780 Mercury Code

1. What does the OBDII code P1780 mean for a Mercury vehicle?

P1780 indicates that the Transmission Control Switch (TCS) circuit is out of the expected self-test range, meaning there may be an issue with the overdrive control system.

2. What are common symptoms of code P1780 in a Mercury?

Symptoms may include the overdrive function not working, the overdrive light blinking, transmission staying in overdrive when it shouldn’t, or reduced fuel efficiency.

3. What causes the P1780 code to appear in a Mercury?

Common causes include a faulty transmission control switch, damaged or corroded wiring, a poor electrical connection, or a malfunctioning Powertrain Control Module (PCM).

4. Can I drive my Mercury with the P1780 code?

While the vehicle may still be drivable, ignoring this code could lead to reduced fuel efficiency or potential transmission issues if the overdrive system isn’t functioning properly.

5. How do you diagnose code P1780 in a Mercury?

A technician will inspect the transmission control switch, check for damaged wiring or connectors, use a scan tool to monitor the switch operation, and verify the signal to the PCM.

6. How can I fix the P1780 code in my Mercury?

Repairs may include replacing the transmission control switch, repairing or replacing damaged wiring or connectors, or reprogramming or replacing the PCM if necessary.

7. Is the P1780 code related to the transmission itself?

P1780 primarily refers to the electrical circuit controlling the transmission’s overdrive function and not the transmission’s mechanical components.

8. What is the transmission control switch in a Mercury?

The transmission control switch, often located on the gear shifter, allows the driver to enable or disable the overdrive function in the transmission.

9. How much does it cost to repair the P1780 code in a Mercury?

The cost varies depending on the exact issue but can range from $50–$200 for a switch replacement and up to several hundred dollars if PCM replacement or reprogramming is needed.

10. Can a weak battery or alternator cause the P1780 code?

While unlikely, voltage issues from a weak battery or faulty alternator can sometimes cause electrical faults that trigger this code, so checking the charging system is recommended.