AutoCodes – Generic – U0120

U0120 Code - Lost Communication With Starter / Generator Control Module

Quick Answer

A Controller Area Network (CAN) is a vehicle bus standard designed to interconnect automotive devices without a host computer. Common causes include Faulty Starter / Generator Control Module, Starter / Generator Control Module harness is open or shorted, Starter / Generator Control Module 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: U0120 indicates Lost Communication With Starter / Generator Control Module .
Common causes: Common causes include Faulty Starter / Generator Control Module, Starter / Generator Control Module harness is open or shorted, Starter / Generator Control Module 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 28,256

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 30, 2020

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code U0120 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 periodic message from the Starter / Generator Control Module has not been received.

OBDII Code U0120 - Lost Communication With Starter / Generator Control Module - AutoCodes.com — U0120 Code - Lost Communication With Starter / Generator Control Module

What does this mean?

What are the Possible Causes of the DTC U0120?

Faulty Starter / Generator Control Module
Starter / Generator Control Module harness is open or shorted
Starter / Generator Control Module circuit poor electrical connection

How to Fix the DTC U0120?

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 U0120 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 U0120 code?

Need more information on how to fix the U0120 code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the U0120 code diagnosed by a professional: Find a repair shop in your area

Information for Specific Makes

U0120 Ford — Lost Communication With Starter/Generator Control Module
U0120 Lincoln — Lost Communication With Starter/Generator Control Module
U0120 Mercury — Lost Communication With Starter/Generator Control Module

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 U0120 Code

1. What are the common symptoms of OBDII code U0120 (Lost Communication With Starter / Generator Control Module)?

- Common symptoms include difficulty starting the vehicle, stalling, or the inability to start the engine altogether.

2. What are the possible causes of OBDII code U0120?

- The code U0120 can be triggered by issues such as a faulty starter or generator control module, damaged wiring, or a poor electrical connection.

3. How can I diagnose the cause of OBDII code U0120?

- Diagnosing the code may involve checking the wiring harness for any visible damage, inspecting the control module for faults, and testing the electrical connections for proper continuity.

4. Can a DIY enthusiast repair OBDII code U0120 at home?

- While some basic troubleshooting steps can be taken at home, diagnosing and repairing the underlying issue causing code U0120 may require professional diagnostic tools and expertise.

5. Is it safe to continue driving with OBDII code U0120 present?

- It is not recommended to drive with the code U0120 active, as it can lead to potential starting or stalling issues, which may compromise the safety and reliability of the vehicle.

6. How much can I expect to pay to repair OBDII code U0120?

- The cost of repairing code U0120 can vary depending on the root cause of the issue, but it may involve expenses for parts replacement, labor, and diagnostic fees.

7. Can a dead battery trigger OBDII code U0120?

- A dead or weak battery can potentially lead to communication issues with the starter or generator control module, resulting in the activation of code U0120.

8. Are there any preventative measures to avoid OBDII code U0120?

- Regular maintenance checks, including inspecting the electrical system and keeping the battery in good condition, can help prevent issues that may trigger code U0120.

9. Will resetting the OBDII system clear code U0120?

- Resetting the OBDII system may temporarily clear the code, but if the underlying issue causing code U0120 is not addressed, the code is likely to reappear.

10. Can code U0120 affect the overall performance of the vehicle?

- Yes, code U0120 can affect the starting and running of the vehicle, potentially leading to performance issues such as poor acceleration, stalling, or difficulty starting the engine.