U1797

SCP (J1850) Lack of Acknowledgment for Door Locks

Network / Communication Chassis/Safety Body Control Network 🟡 Moderate — Fix within a week ⚠️ Drive with Care
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What This Actually Means

In plain language — no jargon

Your vehicle's door lock system isn't communicating properly with the main computer over the SCP bus network. Think of it like sending a text message but never getting a delivery confirmation—the computer sent the command but got no response back.

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Symptoms You May Notice

3 known symptoms for this code
Door locks not responding to remote key fob commands
Door locks unresponsive to interior lock/unlock switches
Warning light or message displayed on dashboard
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How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECU sends commands to the door lock module via the J1850 SCP (Standard Corporate Protocol) bus and waits for an acknowledgment signal within a specific timeout window. If no acknowledgment is received within the expected time frame, the ECU logs a U1797 fault code indicating a communication failure.

Voltage & Parameter Thresholds

ParameterNormal RangeFault Condition
SCP Bus Acknowledgment Timeout ACK received within 100-200ms No ACK received after timeout expires
SCP Bus Voltage 0-5V signaling present No signal or intermittent dropout
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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex
1
Battery terminals and connections
Clean corrosion from battery terminals and tighten connections to restore full electrical voltage to modules.
2
SCP bus wiring harness
Inspect wiring between door lock module and body control module for damage, pinches, or loose connectors.
3
Door lock module
Replace the door lock control module if wiring and connections test good and communication remains absent.
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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code U1797 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 U1797

What happens after you fix the fault

Once the fault is repaired, U1797 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.