Code
U1147
Other
U — Network/User
SCP (J1850) Invalid or Missing Data for Vehicle Security
AI status
Completed
Completed
100%
Causes
- Faulty or intermittent SCP/J1850 physical layer wiring or connectors
- Damaged or poorly grounded module (BCM/ICM/PCM or security module)
- Failed or reprogrammed security/immobilizer module
- Bus short, open, or excessive noise on the J1850/SCP network
- Incorrect module programming or software version mismatch
- Low battery voltage or power supply faults to security module
Symptoms
- Key not recognized, engine immobilized or no-crank/no-start
- Security light illuminated, flashing, or stuck on
- Intermittent or permanent loss of remote lock/unlock or alarm functions
- Other modules reporting related communication errors
- Stored additional U-codes or B-codes related to body/security
What to check
- Read freeze frame and full DTC list from all modules to find related codes
- Inspect battery voltage and ground connections; verify stable supply (12V) during tests
- Visually inspect connectors and wiring for BCM/security module and along SCP/J1850 harness
- Check for aftermarket alarm/remote devices and disconnect for test
- Use a scan tool to monitor security-related messages on the J1850/SCP bus
- Compare module part numbers and software levels if modules were recently replaced
Signal parameters
- Message ID: SCP/J1850 security message frames (manufacturer-specific IDs)
- Expected message frequency: periodic security/state frames (varies by manufacturer)
- Payload contents: immobilizer status, key ID/authorization flags, alarm status (manufacturer-defined bytes)
- Voltage on bus wires: near battery voltage levels referenced to ground (no large transients)
- Bus idle/active levels and waveform integrity (no excessive noise or stuck dominant)
Diagnostic algorithm
- Confirm U1147 present and note any additional codes (document freeze frame and occurrence).
- Verify vehicle battery health and proper charging; ensure voltage ≥12.0V with key off and stable during cranking and testing.
- Inspect physical connectors and wiring at the security module/BCM and along SCP/J1850 network for corrosion, pin damage, or loose terminals; repair as needed.
- With a scan tool, monitor live SCP/J1850 messages for the security frame. Note missing frames, corrupt payloads, or timing anomalies.
- If bus traffic is absent or noisy, probe the bus with an oscilloscope or lab-grade scope capable of J1850 waveform analysis to check signal integrity and timing.
- Disconnect or isolate aftermarket security/remote devices and re-test; remove splices or non-factory taps on the data wiring.
- Swap in a known-good module only if supported by diagnostic procedure (or bench-tested) and re-check communications; follow manufacturer procedures for module coding/immobilizer pairing.
- If module replacement is required, ensure correct software calibration and perform any required programming/initialization per service information.
- Clear codes and test drive/operate accessories to confirm code does not return and normal security functions are restored.
- If problem persists, escalate to manufacturer-specific diagnostic resources or wiring-level repair procedures.
Likely causes
- Loose or corroded connector at the body control/security module
- Failed security/immobilizer module or BCM input conditioning
- Damaged SCP/J1850 wiring (chafed, pinched, or short to power/ground)
- Aftermarket device tied into the data/bus causing invalid frames
- Module with incorrect or incomplete programming after replacement
Fault status
Status
SCP (J1850) Invalid or Missing Data — Vehicle Security message not valid or not received
Repair difficulty: Medium
Diagnostic time: 1-3 hours
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