DTC P1121 (N_SWON): Neutral Position Switch Circuit Low Input (A/T)

1. If DTC P0705 is present, diagnose DTC P0705 first. If DTC P1121 is only code set, turn ignition on. Using voltmeter connected to ground, backprobe PCM connector terminal No. 82 (White/Black wire on Forester and Impreza, or Blue/Red wire on Legacy). If voltage reading is 4.5-5.5 volts, in other positions (not neutral), circuit is normal. Check all connections. If voltage reading is not 4.5-5.5 volts, go to next step.
2. Turn ignition off. Disconnect PCM and transmission harness connector. Check resistance between ground and PCM connector terminal No. 82 (White/Black wire on Forester and Impreza, or Blue/Red wire on Legacy). If resistance is 10 ohms or less, repair short to ground in harness. If resistance is more than 10 ohms, go to next step.
3. Disconnect inhibitor switch connector. Check resistance between transmission connector terminal No. 12 and ground. See Fig 1. If resistance is 10 ohms or less, repair short to ground in harness. If resistance is more than 10 ohms, go to next step.
4. Measure resistance of inhibitor switch between terminals No. 1 and 2 in all gear positions except Park and Neutral. See Figure. If resistance is one megohm or less, replace switch. If resistance is more than one megohm, check selector cable and connection to inhibitor switch. Repair or replace as needed.

Fig 1: Testing Transmission Harness

Courtesy of SUBARU OF AMERICA, INC.