U1233

Code

Other U — Network/User

SCP (J1850) Invalid or Missing Data for Navigation

Brand: Other

Type: U — Network/User

Views: UK: 21 EN: 40 RU: 22

AI status

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Page language: EN

Scan all modules and record U-codes and freeze frame data
Check vehicle battery voltage and charging system under load
Verify fuses and power/ground at the navigation/head unit
Check for SCP/J1850 bus activity with a capable scan tool or oscilloscope
Inspect connectors and wiring to the navigation module for corrosion, pin damage, or poor contacts
Look for recent work or aftermarket devices installed on the data bus

SCP (J1850) bus voltage levels: nominal ~ battery voltage pulses; check for >2 V swing when active
Expected message frequency: periodic navigation/status frames (varies by vehicle, typically multiple messages per second to once per second)
Message presence: navigation module should transmit specific navigation NMEA-like or proprietary frames (module-specific IDs)
Bus idle behavior: no excessive noise, no constant low/high indicating short
Module power: steady 12 V (key on/run) and a good ground

Retrieve and record all stored U-codes and pending codes from all modules. Note any related modules showing comms errors.
Verify vehicle battery state-of-charge and charging system. Poor voltage can cause intermittent comms; correct if outside spec.
Check fuses and supply/ground at the navigation unit. Repair any open circuits and retest.
Inspect physical connectors and wiring harness at the navigation module and at gateway/ junction connectors. Repair corrosion, damaged pins or open/shorted wires.
Use a scan tool to attempt to communicate with the navigation module. If the tool cannot communicate but other modules respond, suspect module power/wiring or module failure.
Monitor the SCP/J1850 bus with a scope or advanced scan tool to confirm expected message activity and identify noise or missing frames. Compare to known-good data if available.
If wiring and power are good but communication is missing, check for module configuration/programming issues. Verify part and software level against OEM information and reflash/update if required.
Disconnect aftermarket devices that attach to the bus (alarms, stereos, telematics) and retest to rule out interference.
As a last step, replace the navigation module or gateway module only after confirming wiring, power, and software are correct. Reprogram and clear codes, then verify repair by road test and rescanning.