2002 Subaru Legacy L P0137 and P0138 O2 Sensor Codes: Fix Without Breaking the Bank
I own a 2002 Subaru Legacy L and have been experiencing intermittent check engine light activation, primarily during summer months. The issue only occurs sporadically at first, but recently it has stayed on continuously. After having the code read, I received both P0137 (Rear O2 Sensor Circuit Low Voltage) and P0138 (Rear O2 Sensor Circuit High Voltage). I'm confused about how a single oxygen sensor can show both low and high voltage readings — is this normal? Given my budget as a college student, I want to avoid expensive repairs. The car still maintains decent fuel efficiency at around 400 miles per tank (approximately 14.5 gallons). Any affordable troubleshooting tips or DIY solutions would be greatly appreciated before I consider professional help.
These codes often point to a loose wiring connection — check the area under the vehicle on the left side, near the rear of the transmission. Alternatively, inspect the ECM connector located beneath the passenger floor carpet. To access it, you'll need to remove the carpet and lift off a metal shield secured with four 10mm bolts. Sometimes simply unplugging and re-plugging the connection resolves the issue. This is a low-cost fix worth trying first.