U1021 – OBD-II DTC

OBD-II DTC U1021 – SCP (J1850) Invalid or Missing Data for Air Conditioning Clutch

DTC U1021 meaning

DTC U1021 refers to a communication issue within the vehicle’s onboard diagnostic system, specifically related to the air conditioning clutch. The code indicates that the data from the air conditioning system is either invalid or missing. This can occur due to problems in the communication network, particularly the SCP (Serial Communication Protocol) using the J1850 standard.

DTC U1021 symptoms

Common symptoms associated with DTC U1021 may include:

• Air conditioning system not functioning properly
• Inconsistent or erratic operation of the air conditioning clutch
• Illumination of the check engine light
• Possible loss of other vehicle functions that rely on the same communication network

DTC U1021 causes

Several factors can lead to the triggering of DTC U1021, including:

• Faulty air conditioning clutch relay
• Wiring issues, such as damaged or corroded connectors
• Malfunctioning air conditioning control module
• Problems with the vehicle’s communication network
• Software glitches in the vehicle’s control modules

DTC U1021 seriousness

DTC U1021 is considered a moderate issue. While it may not pose an immediate safety risk, it can lead to discomfort due to a malfunctioning air conditioning system. Additionally, unresolved communication issues can affect other systems in the vehicle, potentially leading to more significant problems if not addressed.

How to diagnose DTC U1021

To diagnose DTC U1021, follow these steps:

1. Use an OBD-II scanner to confirm the presence of the U1021 code.
2. Check for any additional DTCs that may provide more context.
3. Inspect the wiring and connectors related to the air conditioning system for damage or corrosion.
4. Test the air conditioning clutch relay for proper operation.
5. Examine the air conditioning control module for faults or software issues.
6. Verify the integrity of the vehicle’s communication network.

How to fix DTC U1021 step-by-step instructions

To fix DTC U1021, follow these steps:

1. Repair or replace any damaged wiring or connectors found during the diagnosis.
2. Replace the air conditioning clutch relay if it is faulty.
3. Reprogram or replace the air conditioning control module if necessary.
4. Clear any communication issues in the vehicle’s network by checking for shorts or opens.
5. After repairs, use the OBD-II scanner to clear the DTC and test the air conditioning system.
6. Monitor the system to ensure the DTC does not reappear.

How to erase DTC U1021

To erase DTC U1021, follow these steps:

1. Connect an OBD-II scanner to the vehicle’s diagnostic port.
2. Turn the ignition key to the “On” position without starting the engine.
3. Access the DTC menu on the scanner and locate the U1021 code.
4. Select the option to clear or erase the DTC.
5. Turn off the ignition and disconnect the scanner.
6. Start the vehicle and check if the DTC reappears during operation.

Recommended tools for OBD-II diagnostics

Explore our expert picks: The Best OBD2 Scanners for 2025

Easy-to-use Multimeter for reliable diagnostics: AstroAI Auto-ranging Multimeter

Some of the links on this page may be affiliate links, which means we may earn a small commission if you make a purchase. This helps us keep our DTC database up to date and provide valuable content for free. We only recommend products that we have tested and believe to be the best in their class.