What is an OBD2 code?

An OBD2 (On-Board Diagnostics) code is a diagnostic trouble code (DTC) generated by your vehicle's computer system when it detects a problem. These codes help identify specific issues with your vehicle's engine, transmission, emissions, or other systems.

How do I read OBD2 codes?

To read OBD2 codes, you'll need an OBD2 scanner. Plug it into your vehicle's OBD2 port (usually located under the dashboard), turn your key to the 'ON' position, and follow your scanner's instructions to retrieve the codes. Each code starts with a letter (P, B, C, or U) followed by four numbers.

What do the different types of OBD2 codes mean?

OBD2 codes are categorized by their first letter: P (Powertrain) for engine and transmission issues, B (Body) for interior systems like airbags, C (Chassis) for mechanical systems like brakes, and U (Network) for computer and module communication problems.

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Home » OBD2 Codes » P1748

Code P1748

Symptoms

• Check Engine Light is on

• Transmission may not shift properly

• Reduced fuel efficiency

Common Causes

• Faulty Transmission Control Module

• Software glitch in the TCM

• Poor electrical connections or wiring issues

Glossary

TCM: Transmission Control Module

OBD-II: On-Board Diagnostics, Second Generation

Related Codes

• P1747

• P1749

Official description

Transmission Control Module Self Test

Laymans terms

This code means that the car's computer for the transmission is having trouble checking itself to make sure everything is working right.

Explanation

The Transmission Control Module (TCM) performs a self-test to ensure it is functioning correctly. If it detects an error during this self-test, it triggers the P1748 code.

Technical description

The P1748 code indicates that the Transmission Control Module (TCM) has detected a fault during its self-test routine. This could be due to internal TCM issues, software glitches, or communication errors with other modules.

Diagnosis steps

• Use an OBD-II scanner to confirm the code.

• Inspect the TCM and related wiring for damage or corrosion.

• Check for any software updates for the TCM.

Repair procedures

• Repair or replace damaged wiring or connectors.

• Reprogram or update the TCM software.

• Replace the TCM if necessary.

Tools required

• OBD-II scanner

• Multimeter

• Basic hand tools

Estimated repair cost

$200 - $1000

Difficulty level

Moderate

Commonly affected vehicles

• Ford Explorer

• Lincoln Navigator

• Mercury Mountaineer

Preventive measures

• Regular maintenance and inspection of the transmission system.

• Ensure software updates are applied to the TCM.

• Maintain clean and secure electrical connections.

Error code type

Transmission Control System Issue

User experience recommendations

• Do not ignore the Check Engine Light.

• Have the vehicle diagnosed by a professional if unsure.

• Regularly check for software updates from the manufacturer.

Warranty information

Check with the vehicle manufacturer for warranty coverage on transmission components.

Historical data

This code has been commonly associated with Ford and Lincoln vehicles, particularly in models from the early 2000s.

Urgency level

Moderate – It is important to address this issue to avoid potential transmission damage.

Legal and safety notice

Driving with a malfunctioning transmission can lead to safety issues. Ensure repairs are made promptly.

Testing conditions

• Vehicle must be in a safe and stable condition.

• Transmission fluid should be at the correct level.

Component location

The Transmission Control Module is typically located near the transmission or under the dashboard.

FAQs

Q: Can I drive with a P1748 code?
A: It's not recommended to drive for extended periods with this code as it may lead to transmission issues.

Q: How do I reset the TCM?
A: Resetting the TCM often requires a professional OBD-II scanner or a visit to a dealership.

Last updated: Jan 16, 2026 • Source: internal database

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