October 30: LEMON manuals on a temporary server, it is slow and having issues, download the manuals you need! Later in November we will switch back to the fast server.

Possible Causes

Possible Causes
(K902) O2 RETURN UPSTREAM CIRCUIT SHORTED TO GROUND
(K904) O2 RETURN DOWNSTREAM CIRCUIT SHORTED TO GROUND
(K902) O2 RETURN UPSTREAM CIRCUIT OPEN
(K904) O2 RETURN DOWNSTREAM CIRCUIT OPEN
EXHAUST LEAK
ENGINE MECHANICAL CONDITION
AGING O2 SENSOR
CATALYTIC CONVERTER

Always perform the PRE-DIAGNOSTIC TROUBLESHOOTING PROCEDURE before proceeding.