Hesitation when pressing the gas pedal on your 2020 Subaru Outback, combined with code P2138, indicates the ECM is detecting a voltage correlation error between the two accelerator pedal position sensors. This safety system problem causes the noticeable delay in throttle response.
Subaru's Throttle Safety System
The 2020 Outback, whether equipped with the 2.5L naturally aspirated or 2.4L turbocharged engine, uses dual APP sensors for redundancy. These sensors must provide signals that correlate within a specific relationship. P2138 sets when Sensor D and Sensor E readings don't match the expected correlation, suggesting one sensor may be failing.
Causes of Hesitation with P2138
Common causes include: internal failure of the accelerator pedal sensor assembly, moisture intrusion from floor mat cleaning or water leaks, corroded connector terminals, damaged wiring in the pedal harness, or aftermarket remote start systems improperly connected. Subaru's all-wheel drive vehicles can also experience related issues from transfer case loads affecting electrical systems.
Hesitation Symptoms Explained
The hesitation occurs because the ECM, unsure of true pedal position, delays throttle response while it processes conflicting sensor data. You may notice: a pause of one to two seconds before acceleration begins, jerky response once the car does accelerate, intermittent normal operation, and cruise control that may not engage properly.
Diagnostic Steps
Subaru technicians use the SSM diagnostic system to monitor APP1 and APP2 voltages. They should increase proportionally and within specification as the pedal moves. The voltage relationship is mathematically defined—Sensor D operates at approximately twice the voltage of Sensor E at any given position. Deviation from this relationship triggers P2138.
Fixing the Hesitation
The accelerator pedal assembly replacement resolves internal sensor failures. After installing the new pedal, Subaru's ECM typically self-calibrates during normal driving. Clearing codes and performing a short drive confirms the repair. If hesitation was caused by wiring or connector issues, those repairs are less expensive alternatives.