FixVault

Possible Causes

Possible Causes 
(K399) O2 2/2 HEATER CONTROL CIRCUIT OPEN
(Z902) O2 2/2 HEATER GROUND CIRCUIT OPEN
(K399) O2 2/2 HEATER CONTROL SHORTED TO BATTERY VOLTAGE
O2 SENSOR
PCM

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to  PRE-DIAGNOSTIC TROUBLESHOOTING PROCEDURE  ).