Fuel & intake
Accelerator pedal stops responding (P2138 / P0123 / P0223)
The 2005 car uses a one-year-only potentiometer-type drive-by-wire pedal. As the resistor tracks wear or the connector lets moisture in, the ECM sees the two pedal signals disagree, sets P2138, and drops into fail-safe with no throttle response until the car is restarted.
Frequency basis: The most frequent safety complaint on the 2005 Outback: 42 of 273 NHTSA complaints describe the gas pedal going dead or sudden loss of throttle (NHTSA files most of them under "vehicle speed control", its second-largest category at 40). The main subaruoutback.org thread has 210 replies from 71 participants, with at least a dozen 2005 and 2006 owners reporting the identical fault on its first page alone.
Symptoms
- Pedal goes dead while driving; engine idles but does not respond. Shutting off and restarting (or waiting a few minutes) restores it
- Check engine light with the cruise light blinking; codes P2138, sometimes P0123/P0223 or P0500
- Often happens first thing in the morning or with the HVAC on the floor setting (condensation)
- Reported at 150k–220k miles on 2005 cars, including a 2005 5MT at 220k and a 2005 OBXT at 188k
Causes found
- Worn resistor traces in the 2005-only rheostat pedal sensor (36010AG021); 2006-on cars moved to Hall-effect sensors
- Pedal connector backed off or its gasket misaligned, letting condensation corrode the pins
- Dirty throttle body or throttle body connector (less often)
- One owner traced an intermittent relay behind the glovebox that powers the throttle assembly
Check in this order
- Pull codes: P2138 points at the pedal, P0123/P0223 at a specific pedal circuit
- Unplug, inspect and reseat the pedal connector; look for green corrosion on the pins and check the orange seal
- Watch the pedal position voltages on a scan tool while moving the pedal slowly; look for dropouts
- Check the throttle body connector and clean the throttle body if it is sooty
What fixed it
- Reseating the pedal connector stopped the fault for weeks to a year or more for several owners, but it tends to return
- Replacing the pedal assembly (36010AG021, about $150–190 for the part, a bolt-on DIY job) fixed it for good in the reports that followed up; one 2006 owner got it under warranty for a $100 deductible
- Cleaning the connectors with alcohol lasted about six months; soldering or quick-disconnect splices on the harness did not hold
References on this site
OEM parts
- 36010AG021Accelerator pedal assembly (2005 potentiometer type)
- 16112AA020Electric throttle chamber (throttle body)
Parts diagrams
Factory manual chapters
Sources
Forum threads are owner reports, not factory findings. Counts are from the threads and complaint records read for this page; read the sources before buying parts.
- 1.Code P2138 / Throttle position sensor
subaruoutback.org · Forum thread · 2010–2024, 210 replies, 71 participants; pedal part numbers and fixes
- 2.gas pedal quits again = 2005
subaruoutback.org · Forum thread · 2016; one-year-only rheostat pedal
- 3.Intermittent lack of throttle response
subaruoutback.org · Forum thread · 2023, 2005 5MT at 220k
- 4.2005 - Electronic Throttle not responding? - SOLVED!
subaruforester.org · Forum thread · relay behind the glovebox
- 5.NHTSA complaints, 2005 Subaru Outback
nhtsa.gov · NHTSA · 42 of 273 complaints describe the pedal going dead; 40 filed under vehicle speed control
- 6.Gas Pedal / Accelerator Failure on 2005 Subaru Outback
kimbriggs.com · Article · owner write-up