Error Code P1152 is defined as Lack of Upstream Heated Oxygen Sensor Switch Sensor Indicates Rich Bank 2.

This error code is a generic trouble code, meaning it applies to all vehicles equipped with OBD-II system or vehicles made since 1996 up to present. Specifications on the definition, troubleshooting, and repairs of course, vary from one make and/or model to another.


The A/F sensor or Air-Fuel ratio sensor changes its output voltages depending on the air-fuel ratio. Based on the output voltage, the PC (powertrain control module, also known as ECM or engine control module in other vehicle makes) determines whether the air-fuel ratio is rich or lean, and then adjusts the stoichiometric air-fuel ratio. The PCM also checks the fuel injection volume compensation value to check whether the A/F sensor value is deteriorating or not. This deterioration is determined by both the output voltage variation and fuel and fuel trim variation.

Error Code P1152 is detected when the A/F sensor output voltage change its value outside of the PCM’s expected value.

Common Symptoms

The most common symptom for this error code is the activation of the check engine light on the dashboard.

Possible Causes

Error Code P1152 is usually caused by variable cylinder management system switching from on and off during light throttle conditions, cruising speeds, or when driving on a flat roads. The constant switching causes excessive oil consumption, leading to oil pressure to drop, until it can no longer run the VCM system. Other possible causes include:

  • Faulty Mass Airflow sensor
  • Faulty or leak in Intake Air System
  • Faulty fuel injector
  • Faulty fuel pump
  • Leak in exhaust system, fuel injector or fuel pressure regulator
  • Vacuum leak on engine
  • Fuel pressure too high or too low
  • Faulty or leaking secondary air injection system
  • Faulty PCM (rare)

How to Check

To diagnose this error code, technicians check the following:

  • Check the MAF sensors
  • Check Intake Air Systems for signs of leaks
  • Check fuel pump and fuel injectors
  • Check exhaust system for signs of leaks
  • Check secondary air injection system

How to Fix

Repairs for this error code are as easy as its diagnosis, which include:

  • Repair or replacement of MAF sensors
  • Repairs of leaks or replacement of Intake Air System
  • Repair or replacement of fuel pump and/or fuel injectors
  • Repair of leaks or replacement of leaks in exhaust system
  • Repair or replacement of secondary air injection system

Though seemingly simple, this error code can come alongside with other error codes, which makes it a little tricky to address. It is very important to take your vehicle to your dealer or to a professional technician to have this issue addressed and fixed as soon as possible.