OBD-II Fault Code

P1668: PCM - IDM Communications Error

Meaning, symptoms, likely causes, diagnostic checks and repair guidance for P1668.

System family

Powertrain

Manufacturer-specific

Repair category

Network / communication

Use this category to narrow your checks before replacing parts.

Severity

High

Severity is a general guide. Confirm with scan-tool data and vehicle symptoms.

What P1668 usually means

PCM - IDM Communications Error.

Common symptoms

Check Engine light; Poor drivability or reduced fuel economy depending on fault

Likely causes

Low battery voltage; Blown module fuse; Poor ground; Open/short on communication bus; Module offline

Diagnostic checks

Scan all modules and record freeze-frame data before clearing codes; Check battery voltage and related fuses; Run a full system scan to identify modules not responding; Inspect CAN/SCP wiring, connectors and grounds

Repair guidance

Repair power/ground or network wiring fault first; Only consider module replacement after wiring and power supply checks pass

Verification after repair

Clear code, road-test through the same drive condition, then rescan

Note: Confirm vehicle make/model/year because manufacturer-specific codes can vary; Manufacturer-specific: confirm definition and test steps in the vehicle service manual. A DTC identifies a circuit or system condition, not always the failed part.