OBD2 Car ScannerWhat does U1806 mean?
U1806 stands for SCP (J1850) Lack of Acknowledgment for Primary Id. Two or more of the car's computer modules are not communicating properly over the vehicle network (CAN bus).
Network codes cover the communication between the car's computer modules. When the car's computer sees a reading outside its normal range, it stores this code and may turn on a warning light on the dashboard.
Common causes
- Low or weak battery
- Damaged network wiring or connector
- A module that has lost power or failed
- Aftermarket accessories interfering with the network
What to do
- Read all stored and pending codes with a scanner. Several codes together often point to one cause.
- Note the freeze frame data (speed, temperature, load) recorded when the code was set.
- Inspect the wiring and connectors of the part named in the code for damage, corrosion or looseness.
- Fix the most likely and cheapest cause first, then clear the code and drive to see if it comes back.
Read this code from your own car
Plug in a cheap ELM327 adapter and the app shows every fault code, what it means and how to fix it.
Frequently asked questions
What does U1806 mean?
U1806 means “SCP (J1850) Lack of Acknowledgment for Primary Id”. It belongs to the network communication group: Two or more of the car's computer modules are not communicating properly over the vehicle network (CAN bus).
Is it safe to drive with U1806?
You can usually drive carefully for a short time, but fix it soon to avoid further damage or higher fuel use.
How do I clear U1806?
Fix the cause, then clear the code with an OBD2 scanner or app. If the fault is still there, the code will come back.
Related codes
- U1750SCP (J1850) Lack of Acknowledgment for Audible Warnings
- U1794SCP (J1850) Lack of Acknowledgment for Mirrors
- U1797SCP (J1850) Lack of Acknowledgment for Door Locks
- U1798SCP (J1850) Lack of Acknowledgment for External Access (Doors)
- U1900CAN Communication Bus Fault
- U1950UPB Communication Bus Fault
- U2000Audio Rear Control Unit is Not Responding
- U2001Audio Tape Deck Unit is Not Responding
Code meanings can vary by manufacturer. This page is general guidance, not a repair manual. Always confirm the cause before replacing parts.