Diagnostics · System playbook

Network Communication

U-codes: find the module that stopped answering the phone.

Modern cars are a network of modules on shared buses. U-codes mean modules stopped hearing each other — and the cause splits into three: a dead module, a damaged bus wire, or (most commonly) a power/ground problem making a healthy module go silent. The scariest-looking codes on the scanner are often a blown fuse.

What the symptoms mean

Multiple U-codes across modules
Bus-level problem: shorted wire or one module poisoning the network
One module not responding + its functions dead
That module's power/ground/fuse before the module itself
Gauges dead, no-start, U-codes everywhere
Main bus down — check the star/splice points and OBD port voltages
Codes set only in rain or car wash
Water in a connector on the bus run

The diagnostic order

Work top to bottom — the order is the point. Each step rules out the cheapest, most common causes before anything expensive gets blamed.

  1. Map the complaint: which modules are missing? All missing = bus problem; one missing = that module's supplies.
  2. Check the simple stuff first: fuses for the silent module, and battery/ignition feeds AT the module connector.
  3. Measure the bus at the OBD port: CAN high ~2.6V, CAN low ~2.4V at rest. Both pinned at 0V or 12V, or exactly equal = short on the bus.
  4. Unplug suspects one at a time (or pull the bus fuse segments) — a poisoning module releases the network the moment it is disconnected.
  5. Wiring last: bus wires run in twisted pairs; chafe points at harness brackets and connector water intrusion are the usual suspects.

Tools that matter here

Scan tool that shows module response statusMultimeterWiring diagram — bus topology matters here

The classic mistakes

  • Replacing a module for a communication code caused by its blown fuse.
  • Probing bus wires by piercing insulation and creating tomorrow's corrosion fault.
  • Disconnecting the battery as a "fix" — sleep-mode resets hide the fault until the customer is far away.
Pro tip: The map is the diagnosis: write down which modules answer and which do not, then look at a topology diagram. The break sits between the answering group and the silent group — every time.

Network Communication trouble codes (160)

P0600Serial Communication LinkP0601Internal Control Module Memory Che…P0602Control Module Programming ErrorP0606PCM Processor FaultP0607Control Module PerformanceU0047Control Module Communication Bus D…U0048Control Module Communication Bus D…U0049Control Module Communication Bus D…U0050Control Module Communication Bus E…U0051Control Module Communication Bus E…U0052Control Module Communication Bus E…U0053Control Module Communication Bus E…U0054Control Module Communication Bus E…U0055Control Module Communication Bus E…U0057Control Module Communication Bus E…U0058Control Module Communication Bus E…U0059Control Module Communication Bus E…U0060Control Module Communication Bus F…U0061Control Module Communication Bus F…U0062Control Module Communication Bus F…U0063Control Module Communication Bus F…U0065Control Module Communication Bus F…U0066Control Module Communication Bus F…U0067Control Module Communication Bus F…U0068Control Module Communication Bus F…U0069Control Module Communication Bus F…U0070Control Module Communication Bus G…U0071Control Module Communication Bus G…U0072Control Module Communication Bus G…U0074Control Module Communication Bus G…U0075Control Module Communication Bus H…U0076Control Module Communication Bus H…U0077Control Module Communication Bus H…U0078Control Module Communication Bus H…U0079Control Module Communication Bus H…U0100Lost Communication with ECM/PCMU0101Lost Communication with TCMU0102Lost Communication with Transfer C…U0103Lost Communication with Gear Shift…U0104Lost Communication with Cruise Con…U0105Lost Communication with Fuel Injec…U0106Lost Communication with Glow Plug …U0107Lost Communication with Throttle A…U0108Lost Communication with Exhaust Ga…U0109Lost Communication with Fuel Pump …U0110Lost Communication with Drive Moto…U0111Lost Communication with Battery En…U0112Lost Communication With ECM/PCM AU0114Lost Communication with 4WD Clutch…U0115Lost Communication with ECM/PCM BU0117Lost Communication With GPS Contro…U0118Lost Communication with Alternator…U0119Lost Communication with Battery En…U0120Lost Communication with Starter/Ge…U0121Lost Communication with ABS ModuleU0122Lost Communication with Vehicle Dy…U0123Lost Communication with Yaw Rate S…U0124Lost Communication with Lateral Ac…U0125Lost Communication with Multi-axis…U0126Lost Communication with Steering A…U0127Lost Communication with Parking Br…U0128Lost Communication with Brake Boos…U0129Lost Communication with Brake Syst…U0130Lost Communication with Trailer Br…U0131Lost Communication with Power Stee…U0132Lost Communication with Ride Level…U0133Lost Communication with Suspension…U0134Lost Communication with Active Ste…U0135Lost Communication with TPMS Contr…U0136Lost Communication with Leveling C…U0138Lost Communication with All Terrai…U0140Lost Communication with Body Contr…U0141Lost Communication with Front ECM …U0142Lost Communication with Body Contr…U0143Lost Communication with Body Contr…U0144Lost Communication with A/C Compre…U0145Lost Communication With Body Contr…U0146Lost Communication with Gateway Mo…U0147Lost Communication with Seat Contr…U0148Lost Communication with Seat Contr…U0149Lost Communication with Seat Contr…U0150Lost Communication with Audio Ampl…U0151Lost Communication with Restraint …U0152Lost Communication with Parking As…U0153Lost Communication with Hands-Free…U0154Lost Communication with Gateway Mo…U0155Lost Communication with Instrument…U0156Lost Communication with Electronic…U0157Lost Communication with Digital Co…U0158Lost Communication with Head-Up Di…U0159Lost Communication with Navigation…U0160Lost Communication with Sunroof Co…U0161Lost Communication with Convenienc…U0162Lost Communication with Convertibl…U0163Lost Communication with Navigation…U0164Lost Communication with HVAC Contr…U0165Lost Communication with Rear HVAC …U0166Lost Communication with Auxiliary …U0167Lost Communication with Immobilize…U0168Lost Communication with Passive Re…U0169Lost Communication with Fuel Level…U0170Lost Communication with Blind Spot…U0171Lost Communication with Lane Depar…U0172Lost Communication with Heads-Up D…U0173Lost Communication With Compass Mo…U0176Lost Communication with Forward Ca…U0178Lost Communication with Rain Senso…U0184Lost Communication with Radio Modu…U0195Lost Communication with 4WD Contro…U0196Lost Communication with Rear Camer…U0197Lost Communication with Surround C…U0198Lost Communication With Telematic …U0199Lost Communication with Door Contr…U0200Lost Communication with Headlamp L…U0201Lost Communication with Headlamp C…U0202Lost Communication with Wiper Cont…U0203Lost Communication with Trunk/Lift…U0204Lost Communication with Mirror Con…U0205Lost Communication with Horn Contr…U0206Lost Communication With Chime/Buzz…U0210Lost Communication With Door Switc…U0211Lost Communication With Door Switc…U0212Lost Communication With Steering C…U0213Lost Communication With Overhead C…U0214Lost Communication with Remote Sta…U0215Lost Communication With Door Contr…U0216Lost Communication With Door Contr…U0217Lost Communication With Door Contr…U0218Lost Communication With Door Contr…U0219Lost Communication With Door Contr…U0220Lost Communication With Zone Modul…U0221Lost Communication With Zone Modul…U0222Lost Communication With Zone Modul…U0223Lost Communication With Zone Modul…U0224Lost Communication With Zone Modul…U0225Lost Communication With Zone Modul…U0226Lost Communication With Zone Modul…U0227Lost Communication With Zone Modul…U0228Lost Communication With Zone Modul…U0230Lost Communication with Adaptive S…U0235Lost Communication with Cruise Con…U0236Lost Communication With Cargo Area…U0237Lost Communication With EC/Auto Di…U0242Lost Communication With Instrument…U0243Lost Communication with Trailer Hi…U0244Lost Communication With Instrument…U0245Lost Communication With Instrument…U0246Lost Communication With Instrument…U0247Lost Communication With Instrument…U0253Lost Communication with Collision …U0259Lost Communication With Fuel Fired…U0407Invalid Data Received From GPS Con…U0408Invalid Data Received From Body Co…U0409Invalid Data Received From Body Co…U0410Invalid Data Received From Body Co…U0411Invalid Data Received From Body Co…U0412Invalid Data Received From Body Co…U0427Invalid Data Received From Fuel Fi…U0430Invalid Data Received From Steerin…U0431Invalid Data Received From Body Co…
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