U1118 – OBD-II DTC

OBD-II DTC U1118 – SCP (J1850) Invalid or Missing Data for Primary Id

DTC U1118 meaning

DTC U1118 refers to a diagnostic trouble code indicating “Invalid or Missing Data for Primary Id” in vehicles using the SCP (J1850) communication protocol. This code suggests that the vehicle’s onboard diagnostic system has detected an issue with the data being transmitted from one of the modules, specifically related to the primary identifier. This can hinder communication between modules, affecting various vehicle functions.

DTC U1118 symptoms

Common symptoms associated with DTC U1118 may include:

• Illumination of the check engine light
• Loss of communication with certain vehicle modules
• Erratic behavior of vehicle systems (e.g., ABS, traction control)
• Inconsistent readings on the dashboard
• Potential performance issues, such as reduced power or acceleration

DTC U1118 causes

Several factors can lead to the occurrence of DTC U1118, including:

• Faulty or damaged wiring and connectors in the SCP network
• Malfunctioning control modules
• Software glitches or outdated firmware in the vehicle’s modules
• Corrosion or poor connections at the module terminals
• Interference from aftermarket devices or modifications

DTC U1118 seriousness

The seriousness of DTC U1118 can vary based on the symptoms and the specific vehicle. While it may not immediately affect drivability, it can lead to more significant issues if left unaddressed. Communication failures between modules can result in the malfunction of critical systems, potentially compromising safety and performance.

How to diagnose DTC U1118

To diagnose DTC U1118, follow these steps:

1. Use an OBD-II scanner to confirm the presence of DTC U1118.
2. Check for any additional trouble codes that may provide more context.
3. Inspect the wiring and connectors related to the SCP network for damage or corrosion.
4. Test the affected control modules for proper operation.
5. Verify the integrity of the vehicle’s ground connections.
6. Check for software updates or reprogramming needs for the modules.

How to fix DTC U1118 step-by-step instructions

To fix DTC U1118, follow these steps:

1. Address any wiring or connector issues found during diagnosis.
2. Replace or repair any faulty control modules as needed.
3. Update or reprogram the software in the affected modules.
4. Ensure all ground connections are secure and free of corrosion.
5. Clear the DTC using an OBD-II scanner and test drive the vehicle.
6. Monitor for the reoccurrence of the code or related symptoms.

How to erase DTC U1118

To erase DTC U1118, 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 trouble codes menu on the scanner.
4. Select the option to clear or erase trouble codes.
5. Confirm the action and wait for the scanner to complete the process.
6. Disconnect the scanner and start the vehicle to ensure the code does not return.

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.