TORQDEX // ELECTRICAL DIAGNOSTIC
CAN Bus / Module Communication Problem
Diagnose module communication faults by checking battery voltage, network codes, module power and grounds, CAN wiring, termination, shorts, and individual modules.
01 // WHAT IT MEANS
Understanding the symptom
Modern vehicle modules communicate over shared data networks such as CAN.
A network problem can be caused by low system voltage, a module without power, damaged twisted-pair wiring, incorrect termination, water intrusion, or a module that is electrically disrupting the bus.
02 // QUICK CHECKS
Check these first
Start with simple observations and scan data before moving into deeper testing.
Scan every available module
Determine which modules communicate, which do not, and which network codes are stored.
Check battery voltage first
Low system voltage can create widespread communication faults.
Identify the missing module
A single offline module suggests a different problem than an entire network that is down.
Inspect for water intrusion
Fuse boxes, body modules, connectors, floor harnesses, and network junctions are common moisture-sensitive areas.
03 // SYSTEMS TO CHECK
Common systems involved
Module power and ground
A module cannot communicate if it does not have proper power, ignition feed, or ground.
CAN wiring
CAN networks typically use paired data wires that must remain electrically intact and properly terminated.
Network resistance
Termination resistors help maintain correct signal characteristics on the network.
Bus-disrupting module
An internally failed module can sometimes pull the communication network down.
04 // DIAGNOSTIC ORDER
Diagnose it in this order
Perform a complete network scan
Record every responding and non-responding module before clearing codes.
Verify system voltage
Correct battery and charging issues before diagnosing network communication.
Check power and grounds at missing modules
Do not diagnose network wiring until basic module supply circuits are verified.
Inspect network wiring
Look for damaged twisted pairs, corrosion, aftermarket taps, water intrusion, and poor repairs.
Check network resistance where appropriate
With the system safely powered down, compare bus resistance with the expected network configuration.
Isolate branches or modules
When necessary, disconnect network sections methodically to determine whether one branch or module is disrupting communication.
05 // TEST RESULTS
What the results may indicate
Check its local power, ground, and network branch
A single missing module commonly has a local circuit or module problem.
Check shared network faults
Battery voltage, main bus wiring, gateways, termination, or a bus-disrupting module become stronger suspects.
Inspect that module and branch
A shorted module or wiring branch may be disrupting the bus.
06 // COMMON MISTAKE
Don't replace a module just because the scan tool cannot communicate with it
A module with missing power, ground, ignition feed, or network wiring will appear dead even when the module itself is healthy.
07 // RELATED OBD-II CODES
Related trouble codes
08 // RELATED TORQDEX TOOLS