P0865 TCM Communication Circuit Low

P0865 indicates the TCM communication circuit is low. The network or communication line associated with the transmission module is pulled below range.

Code status

Needs verification

Not yet verified against SAE J2012_202509 / J2012DA. Treat unverified rows as a lookup aid, not repair authority.

System: Transmission
Scope: iso-sae-controlled-p0
Standard: SAE J2012 / ISO 15031-6
Source: legacy-import

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not replace solenoids or sensors while the TCM communication circuit is low or unreliable.

Useful checks before replacing parts

Measure network circuit voltage, check for short-to-ground faults, TCM connector corrosion, water intrusion, and harness damage.
Verify TCM power, ground, wake-up, and scan-tool communication before testing downstream transmission components.
Check whether other modules report matching communication faults or lose transmission data at the same time.

Related OBD-II codes

These nearby transmission entries can help compare wording and fault area. They may share the same verification status as the source database.