SCP Bus Communication Failure U1806
The U1806 code indicates that a control module on the SCP (Standard Corporate Protocol) network, based on SAE J1850 VPW, transmitted a message with a Primary Identifier but did not receive an acknowledgment (ACK) from any other module on the bus. This points to a loss of communication on the low-speed data bus, preventing verification of message integrity.
1. Commonly Affected Makes
2. Most Common Causes
- icon icon-cause">🔧Open or short circuit in the SCP bus wires (SCP+ / SCP-)
- Faulty transmitting or receiving module (PCM, IC, GEM, EATC, etc.)
- Damaged or missing bus termination resistors
- Corrosion or loose connections in data bus connectors
- Excessive electromagnetic interference (EMI) in the wiring harness
3. Symptoms You Will Notice
- Check Engine Light or other warning lights illuminated
- Intermittent or complete loss of communication with certain modules
4. Step-by-Step Diagnosis
Scan for all stored codes and note which modules are not communicating
Inspect SCP bus wiring for opens, shorts, or damage
Check bus termination resistors (typically 120 ohms each) at the end modules
Test module connectors for corrosion or loose pins
Use an oscilloscope to check bus voltage and signal patterns
5. Frequently Asked Questions
Is it safe to drive?▼
The vehicle may still be drivable, but loss of communication can cause erratic behavior or failure of critical systems. It is recommended to diagnose and repair promptly.
How much does it cost to fix?▼
Repair costs vary widely depending on the cause, ranging from $50 for a loose connection to $500 or more for a faulty module.