SCP (J1850) Invalid or Missing Data for Non-Legislated Diagnostics
Your vehicle's communication network (J1850 bus) is missing or corrupted data needed for non-critical diagnostics. Think of it like a radio station losing its signal—the main broadcast still works, but some secondary information isn't getting through.
The ECM monitors the J1850 serial data bus for valid messages from other modules (body control, transmission, ABS). When expected diagnostic data packets fail to arrive or contain invalid checksums for a threshold time, the fault triggers. This is non-legislated data (not emissions-critical), so the engine still runs normally.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| J1850 Message Validity | Valid CRC and data arrival every 100–500 ms | Missing or corrupted frames for >2 seconds |
| Module Response Time | <200 ms response to diagnostic queries | >500 ms or no response |
Code U1090 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.
Once the fault is repaired, U1090 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.