What Does U1177 Mean?
Fourth SCP communication error indicating widespread network issues. The presence of four consecutive Primary ID communication codes (U1174-U1177) points to complete or intermittent network bus failure rather than isolated module problems.
Common Causes
50%
Complete SCP bus circuit failure due to open or short circuit
25%
Central body control or gateway module total failure
15%
Blown fuse or fusible link supplying power to multiple network modules
7%
Main ground strap or battery cable failure affecting all modules
3%
Electrical system damage from jump start or charging system failure
Diagnostic Steps
1
Step 1: Verify all fuses and fusible links related to body control and communication modules
2
Step 2: Test battery cables and main ground straps for high resistance (should be less than 0.2 ohms)
3
Step 3: Access SCP bus at central location and verify bus voltage present (should idle at 2.5-5V bias voltage)
4
Step 4: Disconnect all modules from network and measure bus resistance to identify short circuit if present
5
Step 5: Check for recent jump start, battery replacement, or charging system issues that may have caused voltage spike
Estimated Repair Cost
$150 - $1,500
Parts + labor, varies by vehicle and location
Fourth SCP communication error indicating widespread network issues. The presence of four consecutive Primary ID communication codes (U1174-U1177) points to complete or intermittent network bus failure rather than isolated module problems.
The most common cause of U1177 (SCP (J1850) Invalid or Missing Data for Primary Id) is: Complete SCP bus circuit failure due to open or short circuit
Typical repair costs for U1177 range from $150 to $1,500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Significant loss of vehicle functions likely including possible no-start, inoperative accessories, and warning lights. Vehicle may be unsafe to drive if critical systems are affected.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to U1177 to identify the root cause.
OBDHut Mobile App
Scan codes directly from your car with the OBDHut app.
Coming Soon
Quick Info
Category
Network
System
Vehicle Communication Network
Difficulty
Type
Manufacturer
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
