U1220

SCP (J1850) Invalid or Missing Data for Interior Lamp Outage

Network / Communication Network/Communication SCP Bus Communication Failure 🟡 Moderate — Fix within a week ⚠️ Drive with Care
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What This Actually Means

In plain language — no jargon

Your vehicle's computer isn't receiving proper communication signals about the interior lights from the body control module, like a radio with missing stations. This is a network communication fault on the SCP bus that monitors lighting systems.

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Symptoms You May Notice

3 known symptoms for this code
Interior lights not functioning or behaving erratically
Dashboard warning lights related to body systems illuminated
Communication errors between engine and body control modules
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How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECU monitors SCP (Standard Corporate Protocol) J1850 bus messages from the body control module regarding interior lamp status. It expects valid data packets at regular intervals containing lamp state information. If frames are missing, corrupted, or delayed beyond timeout thresholds, the fault triggers.

Voltage & Parameter Thresholds

ParameterNormal RangeFault Condition
SCP Message Frame Frequency Valid frames received every 100-500ms No valid frame received within 1000ms timeout
Data Checksum Validity Correct CRC/checksum in each message Invalid or missing checksum detected
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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex
1
OBD-II Scanner
Clear the code and monitor for recurrence over several drive cycles to determine if it's intermittent.
2
SCP Bus Wiring and Connectors
Inspect the J1850 bus harness between engine bay and body control module for corrosion, loose connectors, or damage.
3
Body Control Module (BCM)
If wiring is clean, reprogram or replace the BCM as it may have corrupted communication firmware.
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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code U1220 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.

Safety note: OBD-II codes identify the system or circuit where a fault was detected — they do not always identify the exact failed component. A professional mechanic using live sensor data will diagnose the root cause more accurately than replacing parts based on the code alone.
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How to Clear Code U1220

What happens after you fix the fault

Once the fault is repaired, U1220 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.

The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.

✅ Safe to Clear When
  • Fault has been diagnosed and repaired
  • You want to confirm the repair worked
  • Code appeared after a sensor was cleaned
⚠️ Do Not Clear When
  • Preparing for an emissions/PUC test
  • Root cause is still undiagnosed
  • Check engine light is flashing
Emissions test note: Clearing codes resets OBD readiness monitors. Most vehicles need 50–100 km of mixed driving before monitors complete. Do not clear codes immediately before an emissions or PUC inspection.