Error Code P1132 is described as Lack of Upstream HO2S (Heated Oxygen Switch Sensor) Rich Bank 1. Meaning, a rich HEGO (Heated Exhaust Gas Oxygen) sensor indicates a rich condition at the end of a test that it’s trying to correct for over-lean condition. The test fails when fuel control system is no longer capable of detecting switching for a predetermined amount of time.

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 HO2S works by monitoring the malfunction or deterioration that affects emissions. The Upstream HO2S sensor or fuel control is checked for proper output voltage and response rate (time it takes to switch from lean to rich or vice versa). Downstream HO2S sensors on the other hand, are used for catalyst monitor to monitor for proper output of voltage. The ECT (Engine Coolant Temperature), Cylinder Head Temperature (CHT), Inlet Air Temperature (IAT), Mass Air Flow (MAF), Throttle Position (TP) and Crankshaft Position (CKP) sensors provides the input to activate the HO2S monitor.

A fault in HO2S heater circuit is determined by turning the heater on and off and looking for a corresponding change in the OSM and by changing the current that goes through the heater circuit. A fault is detected after two consecutive OBD II drive cycles.

Common Symptoms

As with other error codes Error Code P1132 activates the Check Engine light.

Possible Causes

There are many factors and possible causes for this error code to show up, such as:

  • Faulty Upstream Oxygen Sensor Bank 1
  • High or low fuel pressure
  • Vacuum leak on engine
  • Dirty or defective MAF sensor
  • Leaking fuel injector or fuel pressure regulator
  • Defective PCM (rare)

How to Check

Technicians check multiple things when diagnosing for this error code, which includes checking for:

  • Air leaks after MAF sensor mounting
  • Air leaks in EGR system and connected hoses and/or valves
  • Air leaks in PCV system and connected hoses and/or valves
  • Damaged connectors in HO2S (check pins for damage and moisture)
  • Open, shorted to ground or shorted to voltage HO2S signal circuit
  • Failed HO2S (contaminated with fuel, water, or silicone)
  • Damaged or vacuum hoses leaks

For vehicles with a lean condition, the computer will automatically compensate and could be the one causing the error code. Many times, the MAF sensor gets dirty and must be cleaned. There’s a fine wire between the sensors that vehicle owners can clean using a contact spray cleaner.

For a more thorough diagnosis, technicians may also inspect the following:

  • Base engine mechanical fault (valve timing, compression, etc.)
  • Check for blockage in air cleaner element and air cleaner housing
  • Check the EVAP vapor recovery system (the may be canister is full of fuel)
  • If fuel pressure is too high, then technicians will check for contamination or leaking in the fuel injectors
  • For failed HO2S, technicians will check fuel, silicone, or water contamination

How to Fix

Repairs for this error code are as easy as its diagnosis. Of course, the right repair is achieved from proper diagnosis. Some of the possible repairs are:

  • Repair air leaks at MAF sensor mounting
  • Repair or replace connected hoses or valves on EGR system
  • Repair or replace connected hoses or valves on PCV system
  • Replace damaged HO2S and /or connectors
  • Repair or replace damaged vacuum leaks

Resetting the computer is necessary to see whether the code comes back or not. Also, cleaning the MAF sensor and looking for any loose or disconnected connectors in the engine bay may fix the problem.