U1806 – SCP (J1850) Lack of Acknowledgment for Primary Id

The ODBII code U1806 indicates a communication issue where the vehicle’s network is not receiving an acknowledgment from a module that is expected to respond, specifically related to the SCP (J1850) protocol.

The severity of OBDII code U1806 is moderate.

Common Causes For: U1805 U1805: Transmission Control Module Communication Error

• Faulty communication between modules
• Damaged or corroded wiring or connectors
• Malfunctioning or incompatible control modules
• Software issues or bugs in the control modules
• Low battery voltage or power supply issues
• Interference from aftermarket devices or modifications
• Poor ground connections or grounding issues

Common misdiagnosis for U1806 SCP (J1850) Lack of Acknowledgment for Primary Id

• Faulty wiring or connectors
• Defective control modules
• Incorrectly configured or programmed modules
• Communication issues with other modules
• Battery or power supply problems
• Software glitches or updates needed
• Faulty diagnostic tools or equipment

Common Troubleshooting Steps

The OBD-II code U1806 indicates a communication issue on the SCP (Serial Communication Protocol) bus, specifically related to a lack of acknowledgment for a primary ID. This can occur in vehicles that use the J1850 protocol, which is common in some Ford and Lincoln vehicles. Here are some common troubleshooting steps to diagnose and resolve the U1806 code:

• Check for Other Codes: Use an OBD-II scanner to check for any additional trouble codes. Addressing other codes may resolve the communication issue.
• Inspect the Wiring and Connectors: **Visual Inspection: Check the wiring harness and connectors related to the SCP bus for any signs of damage, corrosion, or loose connections.
• **Connector Pins: Ensure that the pins in the connectors are not bent, corroded, or pushed back.
• Test the SCP Bus: **Multimeter Testing: Use a multimeter to check the voltage levels on the SCP bus. Compare the readings to the specifications in the vehicle’s service manual.
• **Scope Testing: If available, use an oscilloscope to monitor the communication signals on the SCP bus for proper waveform patterns.
• Check for Short Circuits or Open Circuits: Inspect the wiring for any shorts to ground or power, as well as any open circuits that could disrupt communication.
• Inspect Modules on the SCP Bus: Identify all modules connected to the SCP bus (e.g., PCM, ABS, Instrument Cluster) and check for proper operation.
• If a specific module is suspected to be faulty, consider disconnecting it to see if the communication issue resolves.
• Check Power and Ground to Modules: Ensure that all modules on the SCP bus have proper power and ground connections. A lack of power or ground can prevent modules from communicating.
• Perform a Network Test: If available, use a scan tool with network testing capabilities to check the communication between modules on the SCP bus.
• Update or Reprogram Modules: In some cases, a software update or reprogramming of the affected modules may be necessary to resolve communication issues.
• Clear Codes and Test Drive: After performing repairs, clear the trouble codes and take the vehicle for a test drive to see if the code returns.
• Consult Technical Service Bulletins (TSBs): Check for any TSBs related to the U1806 code or communication issues for your specific vehicle make and model. There may be known fixes or recalls.1
• Seek Professional Help: If the issue persists after performing the above steps, consider seeking assistance from a qualified technician or dealership with experience in diagnosing communication issues. By following these troubleshooting steps, you should be able to identify and resolve the underlying issue causing the U1806 code.