P0864

Code

Generic P — Powertrain

TCM Communication Circuit Range/Performance

Brand: Generic

Type: P — Powertrain

Views: UK: 23 EN: 55 RU: 49

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Page language: EN

Read and record all stored codes and freeze frame data from all modules
Verify battery voltage and inspect primary power and ground circuits to TCM
Visually inspect TCM connector and wiring for corrosion, damage, or moisture
Attempt communication with TCM using a scan tool; note if intermittent or absent
Backprobe CAN/LIN/serial pins to confirm signal voltage and activity
Measure bus termination resistance (typically ~60 ohms across CAN H and L)

CAN bus idle voltages: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (nominal)
CAN dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential active)
Bus differential voltage (dominant) ≈ 1.5–2.0 V
Typical CAN bus termination: one 120 Ω resistor at each end (combined ≈ 60 Ω)
LIN/serial lines may be near battery voltage when idle and pulled low to communicate—refer to vehicle-specific values
Module supply: battery voltage present at key-on/run (within ~0.5 V of battery)

Record codes from TCM and other modules; note freeze frame and occurrence conditions.
Verify battery voltage (should be ~12.4–12.8 V at rest, ~13.5–14.8 V while running). Repair charging/battery issues first.
Visually inspect the TCM connector and harness for damage, corrosion, bent pins, or water intrusion. Repair or reseal as needed.
Using a scan tool, attempt to communicate with the TCM. If no communication, check power and ground pins at the TCM connector for proper voltage and continuity to chassis ground.
Backprobe CAN (or other communication) pins with a lab scope or multimeter. Confirm idle voltages and that bus traffic is present. If no activity, isolate upstream modules or bus segments.
Measure resistance across CAN_H and CAN_L with power off; expect near vehicle-specific termination (≈60 Ω). If open or shorted, inspect wiring and modules on the bus.
If voltages are abnormal, trace wiring for short to battery, short to ground, or open circuit and repair damaged wiring/connector.
If bus signals are correct but the TCM still faults, swap with a known-good TCM (if available) or bench-test the TCM per manufacturer procedure. Reflash or update TCM software if TSBs apply.
After repairs, clear codes and perform functional test / road test to confirm the fault does not return.
If intermittent and difficult to reproduce, perform wiggle tests and road test with a scope or a data logger to capture the event.