Error Code P1189 is defined as Fuel Control Bank 2 Sensor 1. This is usually caused by incorrect amount of mixture ratio compensation, or faulty fuel injection system.

This error code is generic trouble code, meaning it applies to all vehicles equipped with OBD-II system, especially 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.


For the Air/Fuel Mixture Ratio Self-Learning Control, actual mixture ratio can be brought closely to the theoretical mixture ratio, based on the mixture ratio feedback signal from the HO2S 1(Heated Oxygen Sensor 1). The PCM (powertrain control module, also known as ECM or engine control module) calculates the needed compensation to correct the offset between the actual and theoretical ratios.

If the compensation value is extremely large (actual mixture ratio is too lean), the PCM will see the condition as a malfunction in the fuel injection system and activate the Check Engine light. In other words, this code is detected when the system does not operate properly, or there is an incorrect amount of mixture ratio compensation.

Common Symptoms

Aside from triggering the Check Engine light, there aren’t many symptoms for this code. As a matter of fact, it doesn’t usually exhibit drivability issues. The most common symptom however, is the increase in fuel consumption.

Possible Causes

There are tons of factors that can cause this error code, some of the most common possible causes are:

  • Intake air leaks
  • Exhaust gas leaks
  • Defective front HO2S (heated oxygen sensor)
  • Misfiring in the ignition
  • Defective fuel injectors
  • Wrong fuel pressure
  • Lack of fuel Faulty Mass Air Flow (MAF) sensor
  • Incorrect Positive Crankcase Ventilation (PCV) hose connection

How to Check

To diagnose for this error code, first check all fuses, circuits and connections to the upstream oxygen sensor. Check the engine for sucking noises, broken vacuum lines, etc. Otherwise, a mechanic can also check the live data from the Air Flow meter.

Then, check the MAF sensor if it’s dirty.

Also, check the ECT sensor and circuit and look for open loop issues.

How to Fix

Repairs for this error code are pretty simple and straightforward, which are of course, can be determined by thorough diagnosis. This includes:

  • Cleaning of the MAF
  • Repair or replace fuel injectors
  • Repair or replace broken vacuum or hoses
  • Replace O2 sensor

Most problems for this error code originate from air leak into the engine, which is due to failed vacuum hose or gasket, or defective air flow meter. These things must be fixed before checking and replacing the oxygen sensor.