What Does U1191 Mean?
A fourth unique module on the SCP network is not providing valid data or is missing from network communication. Multiple U-codes suggest a widespread network issue rather than isolated module failures.
Common Causes
40%
Main network bus open circuit or severe corrosion affecting multiple modules
25%
Failed PCM or BCM causing network master/arbiter problems
20%
Multiple module power supply failure from failed fuse or relay
15%
Individual module failure coinciding with network issues
Diagnostic Steps
1
Step 1: Since multiple U-codes are present, focus on common network infrastructure first
2
Step 2: Check main network bus continuity from DLC to all major junction points
3
Step 3: Inspect central junction box or smart junction box for corrosion or damage
4
Step 4: Test all major module power supply fuses and relays with test light and DVOM
5
Step 5: Disconnect modules one at a time to identify if one module is pulling down the network
Estimated Repair Cost
$200 - $1,500
Parts + labor, varies by vehicle and location
A fourth unique module on the SCP network is not providing valid data or is missing from network communication. Multiple U-codes suggest a widespread network issue rather than isolated module failures.
The most common cause of U1191 (SCP (J1850) Invalid or Missing Data for Primary Id) is: Main network bus open circuit or severe corrosion affecting multiple modules
Typical repair costs for U1191 range from $200 to $1,500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Widespread communication loss may disable critical safety systems including ABS, airbags, or traction control. Vehicle may enter limp mode.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to U1191 to identify the root cause.
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Quick Info
Category
Network
System
Network Communication
Difficulty
Type
Manufacturer
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