AutoCodes – Generic – U0018

U0018 Code - Medium Speed CAN Communication Bus (-) Shorted To Bus (+)

Quick Answer

A Controller Area Network (CAN) is a vehicle bus standard designed to interconnect automotive devices without a host computer. Common causes include Diagnosis of this Diagnostic Trouble Code (DTC) is accomplished via the vehicle symptom(s), Check for more codes, Faulty Control Module. 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: U0018 indicates Medium Speed CAN Communication Bus (-) Shorted To Bus (+).
Common causes: Common causes include Diagnosis of this Diagnostic Trouble Code (DTC) is accomplished via the vehicle symptom(s), Check for more codes, Faulty Control Module.
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 13,063

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 Mar 29, 2020

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code U0018 Description

A Controller Area Network (CAN) is a vehicle bus standard designed to interconnect automotive devices without a host computer. Operating information and commands are exchanged among the devices. The devices have programmed information about what messages are needed to be exchanged on the serial data circuits. CAN bus uses two dedicated wires for communication. The wires are called CAN high and CAN low. When the CAN bus is in idle mode, both lines carry 2.5V. When data bits are being transmitted, the CAN high line goes to 3.75V, and the CAN low drops to 1.25V, thereby generating a 2.5V differential between the lines. Since communication relies on a voltage differential between the two bus lines, the CAN bus is NOT sensitive to inductive spikes, electrical fields, or other noise. The Diagnostic Trouble Code (DTC) sets when a supervised periodic message that includes the transmitter device availability has not been received.

OBDII Code U0018 - Medium Speed CAN Communication Bus (-) Shorted To Bus (+) - AutoCodes.com — U0018 Code - Medium Speed CAN Communication Bus (-) Shorted To Bus (+)

What does this mean?

What are the Possible Causes of the DTC U0018?

Diagnosis of this Diagnostic Trouble Code (DTC) is accomplished via the vehicle symptom(s)
Check for more codes
Faulty Control Module
Control Module harness is open or shorted
Control Module circuit poor electrical connection

How to Fix the DTC U0018?

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 U0018 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 U0018 code?

Need more information on how to fix the U0018 code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the U0018 code diagnosed by a professional: Find a repair shop in your area

Information for Specific Makes

U0018 Ford — Medium Speed CAN Communication Bus (-) Shorted To Bus (+)
U0018 Lincoln — Medium Speed CAN Communication Bus (-) Shorted To Bus (+)
U0018 Mercury — Medium Speed CAN Communication Bus (-) Shorted To Bus (+)

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 U0018 Code

What does the OBDII code U0018 mean?

The U0018 code indicates a problem with the medium-speed CAN (Controller Area Network) communication bus, specifically when the negative bus (-) is shorted to the positive bus (+).

What are common symptoms of the U0018 code?

Symptoms may include illuminated warning lights, loss of communication between modules, erratic vehicle behavior, or failure of certain electronic systems like ABS or power steering.

What causes the U0018 code to appear?

Common causes include damaged wiring, corroded connectors, short circuits in the CAN bus system, or a faulty control module.

Can I drive with the U0018 code active?

Driving with the U0018 code may be possible, but it is not recommended as it can lead to malfunction of critical systems like brakes or steering.

How do I diagnose a U0018 code?

Start by inspecting the CAN bus wiring and connectors for damage, corrosion, or shorts. Use a multimeter to check for continuity and resistance, and scan for module communication errors.

What tools are needed to fix the U0018 code?

Youâ€™ll need an OBDII scanner, a multimeter, and possibly a wiring diagram to trace and test the affected CAN bus circuit.

How is the U0018 code repaired?

Repairs may involve replacing or repairing damaged wiring, cleaning or replacing corroded connectors, or replacing a defective module causing the short.

Can a software issue cause the U0018 code?

While rare, a software issue in a control module could potentially cause communication errors, but physical wiring problems are far more common.

How much does it cost to fix the U0018 code?

The cost varies depending on the issue, with minor wiring repairs costing $100-$300, while module replacement can range from $500-$1,500.

What should I do if the U0018 code returns after repairs?

If the code reappears, recheck the wiring and connectors, ensure all modules are functioning properly, and verify the systemâ€™s resistance meets specifications.