U1099

SCP (J1850) Invalid or Missing Data for Vehicle Speed Control

Network / Communication Network/Communication SCP Bus Speed Data Loss 🟡 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 speed data from the transmission control network, like a GPS losing signal. This breaks cruise control and transmission shift logic because the ECU can't see how fast you're actually going.

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Symptoms You May Notice

3 known symptoms for this code
Cruise control disabled or malfunctioning
Transmission shifting erratically or holding gears too long
Check Engine Light illuminated
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How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECU monitors the J1850 SCP bus for real-time vehicle speed data from the transmission module. It validates this signal's presence and continuity within expected thresholds. Missing or corrupted data frames prevent proper speed-dependent control strategies.

Voltage & Parameter Thresholds

ParameterNormal RangeFault Condition
SCP Bus Signal Presence Continuous valid frames at 10.4 kbps Missing frames or no signal for >500 ms
Vehicle Speed Data Range 0-255 km/h valid transmission reporting Data dropout or implausible values
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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex
1
OBD-II Scanner
Scan for live data to confirm speed sensor dropout and check transmission module communication status.
2
Vehicle Speed Sensor (VSS) or Wiring Harness
Inspect connectors and wiring between transmission and ECU for corrosion, loose pins, or damaged insulation.
3
Transmission Control Module (TCM) Software Update or TCM Replacement
Contact dealer for TCM reflash; if unsuccessful, TCM replacement may be required.
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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code U1099 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 U1099

What happens after you fix the fault

Once the fault is repaired, U1099 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.