SCP (J1850) Invalid or Missing Data for Transmission / Transaxle / PRNDL
Your car's computer isn't receiving shift position data from the transmission, like a driver not telling the engine what gear they're in. The SCP bus (a communication network) is either disconnected or sending garbage information.
The ECM monitors the SCP (J1850) data bus for valid PRNDL (Park-Reverse-Neutral-Drive-Low) position signals from the transmission range sensor. The ECU expects periodic, valid messages within a specific timeframe; if data is missing, corrupted, or fails checksum validation for longer than a threshold period, the fault is triggered.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| SCP Message Frequency | Valid PRNDL data every 100-200 ms | No valid message for >500 ms or checksum failure |
| PRNDL Signal Validity | Single, valid gear position state | Invalid state, multiple simultaneous positions, or out-of-range value |
Code U1059 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, U1059 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.