SCP (J1850) Invalid or Missing Data for Engine Coolant
The engine computer isn't receiving coolant temperature data over the vehicle's communication network (like a dropped phone call between sensors). Without this info, the engine can't properly adjust fuel and ignition timing.
The ECM expects valid coolant temperature data transmitted via the SCP (J1850) bus every scan cycle. The sensor should report temperatures between -40°C and 125°C. If the ECM doesn't receive this message or receives invalid data, it triggers this code.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Coolant Temp Signal (SCP Bus) | -40 to 125°C with valid message | Missing, delayed, or out-of-range data on bus |
| Message Timeout | Data received every ~100ms | No valid message for >500ms |
Code U1073 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, U1073 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.