U1120 Code: Meaning, Causes, and Symptoms (100% Fixed!)

The U1120 code is an OBD-II diagnostic trouble code that indicates a communication error between the ABS control module and other vehicle modules.

This code can be triggered by various causes, such as faulty wiring connections, damaged sensors, or a malfunctioning ABS control module. Symptoms of the U1120 code may include an illuminated ABS warning light on the dashboard, disabled traction control system, or issues with the stability control system.

In this article, we will explore the meaning behind the U1120 code, its possible causes, and common symptoms associated with it. Understanding these aspects can help diagnose and resolve potential issues with your vehicle’s ABS system efficiently.

What is the U1120 code?

The U1120 code is a diagnostic trouble code (DTC) that refers to a communication problem between the vehicle’s electronic control modules (ECMs). This specific code is often found in Chrysler, Dodge, and Jeep vehicles.

Here are some key points about the U1120 code:

• Definition: The U1120 code indicates that there is a loss of communication with the ABS module.
• Causes: There can be several causes for this code to appear, including wiring issues, faulty sensors or solenoids, problems with the ABS module itself, or software glitches.
• Symptoms: Common symptoms associated with the U1120 code include an illuminated malfunction indicator lamp (MIL), traction control and/or stability control system malfunctions, and possibly even drivability issues.
• Diagnosis: To diagnose this issue accurately, a qualified technician will use an OBD-II scanner to retrieve all stored codes from the ECM. They will also inspect related components for any signs of damage or corrosion.
• Repair Options: Repairing the U1120 code depends on its underlying cause. Some common repair options may involve fixing damaged wiring connections, replacing faulty sensors or solenoids if needed. In more severe cases where there are internal faults within the ABS module itself detected during diagnosis, it might need replacement.
• Preventive Measures: Regular maintenance checks can help prevent potential issues by ensuring proper functioning of all electrical connections and components involved in vehicle communications.

It’s important not to ignore or dismiss DTCs like the U1120 as they could indicate potentially serious problems within your vehicle’s systems.

If you encounter this error code or experience any associated symptoms mentioned above it’s recommended consulting a professional mechanic who can properly diagnose and resolve these issues.

Common Causes of the U1120 Code:

When encountering the U1120 code, there are several common causes that could be triggering this error. These causes include:

1. Faulty ABS Wheel Speed Sensor: A malfunctioning ABS wheel speed sensor is a frequent culprit behind the U1120 code. This sensor plays a crucial role in monitoring the rotational speed of each wheel. If it fails to provide accurate data, it can trigger the U1120 code.
2. Damaged Wiring or Connections: The wiring harness and connectors responsible for transmitting signals from various components may become damaged over time due to wear and tear or environmental factors such as moisture or heat exposure. Faulty connections or frayed wires can result in communication errors between modules and lead to the U1120 code being stored.
3. Defective ABS Control Module: The ABS control module is responsible for interpreting data received from sensors and making decisions accordingly. If this module becomes faulty, it may send incorrect signals or fail to communicate with other modules effectively, resulting in an erroneous U1120 code.
4. Malfunctioning Powertrain Control Module (PCM): In some cases, a malfunctioning PCM can also trigger the U1120 code by failing to establish proper communication with other control modules within the vehicle’s network.
5. Low Battery Voltage: Insufficient voltage supply caused by a weak battery or charging system issues may cause intermittent communication problems between modules, leading to the storage of false trouble codes like U1120.

To diagnose and resolve these common causes effectively, it is recommended to consult a professional automotive technician who has access to diagnostic equipment capable of communicating with relevant vehicle systems.

Symptoms of a U1120 Code:

• Engine may stall or have difficulty starting.
• Reduced engine power and performance.
• Transmission may not shift properly or go into limp mode.
• Check Engine Light (CEL) will be illuminated on the dashboard.
• Vehicle may experience intermittent hesitation or jerking during acceleration.
• ABS, traction control, or stability control warning lights may also be activated.

Engine stalling/starting issues:

The engine might periodically stall while idling or have trouble starting. This can make it difficult to operate the vehicle reliably.

Reduced engine power/performance:

A U1120 code can cause a noticeable decrease in engine power and overall performance. The vehicle may struggle to reach higher speeds or accelerate as expected.

Transmission problems/Limp mode activation|

Miscommunications between various systems due to the U1120 code can affect transmission operation.

The transmission might not shift smoothly or engage gears properly, potentially leading to the activation of limp mode where the vehicle is limited to low speeds and specific gear ratios for protection purposes.

Check Engine Light (CEL) illumination:

When a U1120 code is detected by the onboard diagnostics system, it triggers an alert that illuminates the Check Engine Light on your dashboard.

This serves as an indication that there is a problem with one of these interconnected systems within your vehicle’s network.

It is essential to address this issue promptly and diagnose any underlying problems using appropriate diagnostic equipment such as an OBD-II scanner.

Watch this video to fix this issue:

How to Diagnose the U1120 Code?

To diagnose the U1120 code, follow these steps:

1. Check for other trouble codes: Use an OBD-II scanner to check if there are any additional trouble codes stored in the vehicle’s computer system. Addressing other codes may help resolve the U1120 code.
2. Inspect wiring and connectors: Inspect all wiring and connectors related to the ABS control module, wheel speed sensors, and steering angle sensor. Look for any signs of damage, corrosion, or loose connections. Repair or replace as necessary.
3. Test battery voltage: Check the battery voltage using a multimeter while the engine is running. Low voltage can cause communication issues between modules in the vehicle’s network.
4. Perform a visual inspection of components: Visually inspect components such as wheel speed sensors and their reluctor rings for any physical damage or debris that could obstruct proper operation.
5. Test ABS control module power supply: Test the power supply to the ABS control module by checking for proper voltage at its connector pins with a multimeter.
6. Check CAN bus lines: Using a scan tool capable of monitoring live data, check for proper communication on both high-speed (CAN-H) and low-speed (CAN-L) CAN bus lines connected to relevant modules involved in ABS operations.
7. Verify steering angle sensor readings: Ensure that the steering angle sensor is providing accurate readings during straight driving and turning maneuvers using a diagnostic scan tool capable of accessing live data.
8. Perform road test procedures: Take the vehicle on a road test while monitoring live data from various sensors associated with ABS functions to identify any abnormal behavior or inconsistencies.
9. Consult technical service bulletins (TSBs): Check manufacturer-provided TSBs specific to your vehicle make/model regarding known issues related to U1120 code diagnosis and repair recommendations.

Note: The U1120 code can be challenging to diagnose accurately. If you’re unsure or unable to perform these diagnostic steps yourself, it’s recommended to seek assistance from a qualified automotive technician who has experience with ABS systems and diagnostic procedures.

Steps to fix the U1120 code:

To resolve the U1120 code and get your vehicle back on track, follow these steps:

1. Check for loose or damaged wiring: Inspect all wiring harnesses and connectors related to the ABS control module. Look for any signs of wear, corrosion, or loose connections. If you find any issues, repair or replace the affected components.
2. Inspect wheel speed sensors: Examine each wheel speed sensor for damage or debris accumulation that may affect its functionality. Clean the sensors if necessary and ensure they are properly mounted.
3. Verify sensor alignment: Make sure that the wheel speed sensors are aligned correctly with their corresponding tone rings or reluctor wheels. Misalignment can cause inaccurate readings, triggering fault codes like U1120.
4. Check ABS control module power supply: Test the power supply to the ABS control module using a multimeter or similar diagnostic tool. Ensure there is proper voltage reaching the module; otherwise, investigate and address any electrical issues causing inadequate power delivery.
5. Perform an ABS system reset: Use a professional-grade scan tool to perform an ABS system reset procedure according to your vehicle’s manufacturer instructions. This will clear any stored fault codes and reinitialize various system components.
6. Test drive your vehicle: After completing all repairs and resets, take your vehicle for a test drive under normal operating conditions to verify if the U1120 code returns.
7. Seek professional assistance (if needed): If you’ve followed all previous steps without success in resolving the issue yourself, it may be time to consult a professional mechanic who has experience with diagnosing complex automotive electronic systems like ABS modules.

Remember that these steps provide general guidance for fixing a U1120 code but may not cover every possible scenario specific to your vehicle model and year of production

Tips for Preventing the U1120 Code from Reappearing:

To prevent the U1120 code from reappearing in your vehicle, follow these helpful tips:

1. Regular Maintenance: Stay on top of your vehicle’s regular maintenance schedule to ensure all components are functioning properly.
2. Check Transmission Fluid: Regularly inspect and maintain proper transmission fluid levels as recommended by your vehicle’s manufacturer.
3. Inspect Wiring Connections: Routinely check wiring connections related to the ABS module and wheel speed sensors for any signs of damage or corrosion. Repair or replace as necessary.
4. Keep Tires in Good Condition: Maintain proper tire pressure and regularly inspect tires for wear patterns or damage that could affect wheel speed sensor readings.
5. Avoid Harsh Driving Conditions: Try to avoid driving in extreme conditions such as off-roading, excessive heat, or heavy snowfall that can put stress on the ABS system.
6. Be Mindful of Brake Fluid Quality: Regularly check brake fluid levels and keep an eye out for any contamination or degradation issues that may impact ABS performance.
7. Address Other Related Codes Promptly: If you encounter any additional codes associated with the U1120 error, address them promptly to avoid potential complications down the line.
8. Seek Professional Help when Needed: If you’re unable to resolve the issue yourself or if you lack technical expertise, it’s best to consult a qualified mechanic who can diagnose and repair any underlying problems causing the U1120 code.

Remember, taking proactive measures towards preventing recurrence of the U1120 code is essential in maintaining optimal vehicle performance and safety.

Other Related Trouble Codes to Consider:

When diagnosing the U1120 code, it can be helpful to consider other related trouble codes that may provide additional insights into the underlying issue. Here are some codes worth considering:

1. U1110 – SCP (J1850) Invalid or Missing Data for Primary Id: This code indicates a communication problem between various control modules in the vehicle. It is advisable to check for any loose connections, damaged wiring, or faulty control modules.
2. P0404 – Exhaust Gas Recirculation Circuit Range/Performance: This code points towards an issue with the EGR (Exhaust Gas Recirculation) system. It could be caused by a malfunctioning EGR valve, clogged passages, or an electrical problem within the circuit.
3. P0605 – Internal Control Module Read Only Memory (ROM) Error: This code suggests an internal error within one of the vehicle’s control modules. Possible causes include a faulty module, power supply issues, or software glitches.
4. C121C – Torque Request Signal Denied: This code relates to transmission-related problems and typically occurs when there is a discrepancy between torque requested by the engine and actual torque delivered by the transmission.
5. B2205 – Front Wiper Relay Coil Open Circuit : This code signifies an open circuit in the front wiper relay coil circuitry which may prevent proper operation of windshield wipers during adverse weather conditions.

It is important to note that while these codes are related to U1120 in some way, they may not directly address its specific causes or symptoms.

However, considering these additional trouble codes can provide valuable clues and help streamline diagnosis efforts.

Please consult your vehicle’s service manual or seek professional assistance if you encounter any of these trouble codes alongside U1120 as they require specialized knowledge and equipment for accurate diagnosis and repair.

Understanding Vehicle Communication Networks:

In modern vehicles, communication networks play a crucial role in the overall functionality of various systems.

These networks allow different components and modules within a vehicle to exchange information and work together seamlessly.

Here’s a breakdown of some key points to help you understand vehicle communication networks:

1. Purpose of Communication Networks: The primary purpose of these networks is to facilitate data transfer between different electronic control units (ECUs) present in the vehicle. ECUs are responsible for controlling various functions like engine management, transmission, braking system, airbags, infotainment systems, and more.
2. CAN Bus System: One commonly used communication network is the Controller Area Network (CAN). It allows high-speed data transmission between ECUs using two-wire serial communication. CAN bus provides reliable and efficient communication while reducing wiring complexity.
3. LIN Bus System: Another type of network found in vehicles is the Local Interconnect Network (LIN). This low-cost bus system enables slower speed communications primarily used for non-critical functions such as interior lighting controls or window operations.
4. MOST Bus System: The Media Oriented Systems Transport (MOST) bus is utilized mainly for multimedia applications like audio and video streaming in modern cars with advanced entertainment systems.
5. Diagnostic Protocols: Onboard Diagnostics II (OBD-II) protocol enables standard diagnostic capabilities by providing access to real-time sensor data and trouble codes stored within ECUs via standardized connectors under the dashboard.
6. Symptoms of Communication Issues: When there are problems with the vehicle’s communication network or individual ECUs fail to communicate effectively, it can lead to symptoms like intermittent loss of functionality or erratic behavior across multiple systems.
7. Causes of Communication Failures: Common causes include damaged or loose wiring connections, faulty connectors, water ingress into electrical components, software glitches within ECUs, or even physical damage due to accidents or extreme conditions.

Understanding vehicle communication networks is crucial for diagnosing and resolving issues effectively. By having a basic understanding of these networks, both technicians and car owners can better comprehend the complexities involved in troubleshooting modern vehicles.

Frequently Asked Questions about the U1120 Code:

What does the U1120 code mean?

The U1120 code is a generic powertrain code that indicates a communication problem between the transmission control module (TCM) and the engine control module (ECM). It usually means there is an issue with the TCM not receiving or transmitting data properly.

What are some common causes of the U1120 code?

The most common causes of the U1120 code include:

• Faulty wiring connections or harnesses.
• Malfunctioning TCM or ECM.
• Poor electrical connections.

What are some symptoms of the U1120 code?

When your vehicle experiences a U1120 code, you may notice one or more of these symptoms:

• Transmission shifting problems.
• Engine stalling or hesitation.
• Reduced fuel efficiency.
• Illuminated Check Engine Light.

Can I drive my vehicle with a U1120 code?

It is generally not recommended to drive your vehicle when it has a stored trouble code like U1120.

Continuing to drive can potentially cause further damage to your transmission system and other related components.

It’s advisable to have your vehicle inspected by a qualified mechanic as soon as possible.

How much does it cost to fix a U1120 error?

The cost of fixing a U1120 error can vary depending on several factors, including labor rates in your area, parts needed for repair/replacement, and any additional diagnostic work required.

It’s best to consult with an experienced mechanic who can provide you with an accurate estimate based on your specific situation.

Remember, if you encounter a trouble code like U1120, it’s important to address it promptly and seek professional help from trained technicians to ensure proper diagnosis and repair.