P1656 — CAN Link PCM PCM Circuit Network

Diagnostic algorithm

1. Record all DTCs and freeze frame, then disconnect scanner and attempt to communicate again to confirm persistence.
2. Verify battery/charging system condition. Low voltage can cause network faults—repair as needed.
3. Inspect PCM power and ground circuits. Verify fuses and relay(s) feeding the PCM and gateway are intact and supplying proper voltage/ground.
4. Visually inspect PCM connector and harness for damage, corrosion, bent pins or water intrusion. Repair or replace damaged connectors/wiring.
5. With ignition ON (engine off), measure CANH and CANL voltages at the PCM connector and at other accessible modules. Compare to expected values in signal_params.
6. With ignition off, measure resistance between CANH and CANL at one end of the bus to check termination (should be ~54–70 Ω). If out of range, inspect for missing/shorted termination or disconnected module.
7. Use a professional scan tool to poll modules on the bus to identify which modules respond. Note any modules that do not communicate or report errors.
8. If physical inspection and basic electrical checks pass, use an oscilloscope to view CAN signals while attempting communication. Look for noise, missing frames, dominant stuck states, or distortions indicating bus faults.
9. Isolate the fault by disconnecting suspected modules (one at a time) or splicing points and rechecking bus voltages/resistance until the fault disappears; repair the wiring or replace the faulty module discovered.
10. After repair, clear codes, cycle ignition, and verify normal communication with all modules, and road test to confirm the fault does not return.
11. Safety note: Before disconnecting modules, follow OEM procedures (ignition off, key removal) and be aware that disconnecting certain modules may disable vehicle systems.