What Does U1221 Mean?
Secondary communication error for interior lamp outage monitoring on the SCP network. Represents a redundant or additional data parameter for interior lighting fault detection that is missing or corrupted.
Common Causes
35%
Body control module internal circuit failure specific to interior lighting
30%
Instrument cluster not receiving interior lamp status data
20%
Door modules losing communication with central body control
15%
Network wiring damage in door jamb or pillar area from repeated flexing
Diagnostic Steps
1
Step 1: Compare freeze frame data between U1220 and U1221 to identify specific affected circuit
2
Step 2: Check for proper operation of courtesy lights in all doors
3
Step 3: Inspect door harness connectors and wiring for damage at flex points
4
Step 4: Use scan tool to command interior lights on/off and observe network response
5
Step 5: Check for loose or corroded ground connections at body control module
Estimated Repair Cost
$90 - $450
Parts + labor, varies by vehicle and location
Secondary communication error for interior lamp outage monitoring on the SCP network. Represents a redundant or additional data parameter for interior lighting fault detection that is missing or corrupted.
The most common cause of U1221 (SCP (J1850) Invalid or Missing Data for Interior Lamp Outage) is: Body control module internal circuit failure specific to interior lighting
Typical repair costs for U1221 range from $90 to $450, depending on the vehicle, location, and whether you do it yourself or go to a shop.
No significant safety concerns. Interior lighting warning system may not function, requiring manual inspection of interior bulbs.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to U1221 to identify the root cause.
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Quick Info
Category
Network
System
Vehicle Communication Network / Interior Lighting System
Difficulty
Type
Manufacturer
Recommended Tools
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