Possible causes

– Fuel delivery system
– Manifold Absolute Pressure (MAP) sensor or wiring connectors
– O2 sensor wiring or connectors
– Engine mechanical system
– Faulty Powertrain Control Module (PCM)

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)

P1128 JEEP Description

The Powertrain Control Module (PCM) detects a condition where the vehicle has remained in open loop fuel control, from a start-up condition, longer than a calibrated amount of time, when conditions would have otherwise closed loop operation.

JEEP Technical Service Bulletins for P1128 code