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2001 Subaru Forester P0500, P1540, P1590, P1591: Green OBD2 Connector Issue & Code Behavior Explained

Model: 2001 SUBARU FORESTER Fault Code: P0500 Posted: 2008-07-27 07:47

While inspecting the under-dash OBD2 port on my 2001 Subaru Forester, I discovered a male and female two-prong green electrical connector that was unplugged. After reconnecting it, the engine check light begins flashing, and the OBD2 reader displays four persistent fault codes: P0500, P1540, P1590, and P1591. These codes remain active even after attempting to clear them via the OBD2 system. However, when I disconnect the green connector, the check engine light turns off and no codes appear upon restarting the engine. The question is: Are these fault codes legitimate or are they triggered by connecting this green harness? What is the function of this green connector in relation to the OBD2 diagnostic circuitry on the 2001 Forester? Mike

Related fault codes
P0500P1540P1590P1591
Comments (3)
Anonymous 2008-07-27 10:58

The green connector may serve as a diagnostic jumper for auxiliary systems within the vehicle. It could be designed for optional features or equipment not installed in your model. Connecting it might interfere with communication between modules, leading to false or transient error codes. If everything operates normally when disconnected, it's safest to leave the connector unplugged. A Subaru dealership may provide more specific insight into its purpose.

Anonymous 2010-01-11 23:23

I recommend disconnecting the green wire under the dash. I contacted a Subaru dealer regarding similar issues with my 1999 Outback and was advised that this connector should remain unplugged to avoid triggering diagnostic errors or false codes.

Anonymous 2010-02-16 18:42

Hi Mike, The green connectors originated from the OBDI era. Subaru continues to include them on current models in certain markets like Australia, primarily for quick diagnostics by home mechanics—commonly known as a 'U check'. While OBDII has largely replaced this method, these connectors are still provided in some regions due to differences in ECU configurations. In the past, connecting the two terminals would cause the engine warning light to flash a code sequence: long flashes followed by short ones. For example, three long flashes and two short flashes (32) indicated an oxygen sensor issue. No flashes meant no problem. The flashing you're experiencing is likely due to ECU software confusion when the connector is active. Since you have access to an OBDII scanner, rely on that system instead. Simply disconnect the green connectors and secure them with tape—ensure they are fully disconnected—to prevent interference. Ignore these codes and focus on verified diagnostics through OBDII.