Possible causes

– Faulty Heated Oxygen Sensor (HO2S) Bank 1 Sensor 1
– Vacuum leak
– Faulty Heated Oxygen Sensor (HO2S) Bank 1 Sensor 1 harness is open or shorted
– Faulty Heated Oxygen Sensor (HO2S) Bank 1 Sensor 1 circuit poor electrical connection

When is the code detected?

If the Powertrain Control Module (PCM) determines that the front HO2S did not switch enough times, the PCM will set the P1133 code.

Symptoms

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

P1133 GMC Description

The Powertrain Control Module (PCM) monitors the Heated Oxygen Sensor (HO2S) activity for 90 seconds after closed loop operation has begun. The PCM determines if the front HO2S is functioning properly by counting the number of HO2S-1 Lean/Rich (L/R) and Rich/Lean (R/L) switches.