P2773 indicates the powertrain control module (PCM) has detected a low voltage signal from the four-wheel-drive low-range switch circuit. The 4WD low switch tells the PCM when the transfer case is engaged in 4-low; a 'low' reading means the signal wire is shorted to ground, the switch is stuck closed, or the circuit has an open/short that pulls the reference voltage down.
The switch itself is the most common failure point. Internal contacts wear, stick, or fail open/closed, producing a persistent low signal to the PCM.
Chafed, pinched, or melted wires in the transfer-case harness can short the signal circuit to ground, which the PCM reads as a low input.
Moisture and road contamination at the transfer-case connector is common and can create a high-resistance or shorted path to ground.
If the switch plunger does not line up with the transfer-case shift rail, it may be held in the low-signal position even when 4-low is not selected.
On some vehicles the 4WD low function is read by a position sensor inside the transfer case; a failed sensor can produce the same low-signal code.
Rare. The control module can only be considered after the switch, wiring, connector, and sensor have all been verified, because circuit-level codes almost never trace to the module itself.
Usually yes for normal 2WD or 4-high driving. The code typically only affects 4-low engagement, but the underlying wiring or switch fault should be repaired soon to avoid being stranded when 4WD is actually needed.
Almost never. P2773 is a circuit code, not a mechanical-range code. The transfer case itself is rarely the cause; the switch, sensor, or wiring is the usual culprit.
No. Despite what some online sources suggest, the PCM is one of the least likely causes of a circuit-low code. Replacing the module without first proving the wiring, connector, switch, and range sensor are good is an expensive mistake. Most P2773 faults are resolved at the switch or harness level.
With the connector disconnected, the switch is checked for continuity between its terminals in each transfer-case position and compared to the manufacturer's spec. With the connector plugged in, the signal wire is back-probed to confirm the PCM is sending a reference voltage and that the voltage changes correctly when 4-low is selected.