Error Code P2197 is defined as O2 Sensor Signal Stuck Lean Bank 2 Sensor 1.

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


Error Code P2197 means there’s a problem with the O2 (oxygen) sensor problem.  Though several things can cause an O2 sensor to fail, the most common cause is a vacuum leak in the intake manifold on bank 2 (for this code). Bank 2 is the group of cylinders that DON’T have the ‘Number 1’ cylinder; bank 1 is the group of cylinders containing the number one cylinder.

The PCM (powertrain control module, also known as ECM or engine control module) monitors the Air/Fuel ratio of the exhaust through the O2 (oxygen) sensors and tries to keep things at a normal air/fuel ratio of 14.7:1. The O2 A/F sensor outputs a voltage reading which the PCM uses. This code means there’s a lean Air/Fuel ratio read by the PCM, meaning there is too much oxygen in the mixture and has strayed away from the ideal ratio, and that the PCM can no longer correct it.

For some vehicles like Toyotas, this code refers to A/F (Air/Fuel ratio) sensors, which are more sensitive versions of oxygen sensors.

Other similar codes include:

Common Symptoms

As with other error codes, this code activates the Check Engine light and registers the code to the vehicle’s memory system. Other symptoms include:

  • Possible overheating
  • Engine misfire
  • Low power output

Possible Causes

As with other error codes, this code activates the Check Engine light and registers the code to the vehicle’s memory system. Other symptoms include:

  • Defective Oxygen (O2) or A/F ratio sensor or sensor heater
  • Open or short in O2 sensor circuit (harness, wiring)
  • Problem in the fuel pressure or fuel injector
  • Leaks in the intake air or engine vacuum
  • Defective fuel injector(s)
  • Fuel pressure too high or too low
  • PCV system leak/fault
  • Defective A/F sensor relay
  • ECT sensor malfunction
  • MAF sensor malfunction
  • Low fuel pressure too
  • Fuel Leak
  • Air suction in air intake system
  • Defective PCM

How to Check

As with other error codes, diagnosing this code requires a scan tool to monitor both the short term and long term fuel trim values and the O2 sensor or Air/Fuel ratio sensor readings. Technicians also look at the freeze frame data to see the conditions when the code was set. This will help them determine whether the O2 A/F sensor is working properly. Then, they will compare their data with the values set by the manufacturers.

Whenever there is no available scan tool, a multimeter scanner can be used to back probe the terminals on the O2 sensor wiring connector. Technicians will check for ground, short to power, open circuits, etc. Then compare the specs to the specs set by the manufacturer.

Next, they inspect the connectors and wirings that lead to the sensor. They look for loose connections, chaffed or rubbed wires, melted wires, etc. and repair as needed.

Next, they check the vacuum lines and look for leaks. Carburetor cleaner or propane can also be used to check for vacuum leaks for the hoses while the engine is running. If the RPM changes when a vacuum leak is being checked, then there’s likely a leak. This step can be tricky and dangerous, which is why technicians usually have a fire extinguisher within reach in case something goes wrong. For many Ford vehicle models, the hose that runs from the PCV to the throttle body can melt, causing code P2195, P2197, P0171, or P0174.

If it’s been determined that vacuum leak is the problem, then all vacuum lines must be replaced, especially if they’re older and getting brittle.

Next, technicians perform fuel pressure test to verify the readings and compare them with the specs set by the manufacturers.

If you have the budget and you only have an engine with more than one bank, and the problem is only with one bank, you can simply swap the sensor from one bank to the other. Then clear the code, and see if the code is followed to the other bank. This will tell you if it’s the sensor/heater itself that’s failed.

How to Fix

The most common repair for this code is simply replacing the O2 sensor or repairing the vacuum leak. Of course, other components can also create a problem and lead to this code, and must be repaired through:

  • Repair or replacement of damaged or corroded harness
  • Replacement of defective PCM
  • Repair of PCV system leak (valve and hose)
  • Replacement of the MAF sensor
  • Repair or replacement of ECT (engine coolant temperature) sensor

When replacing O2 or AF sensors, make sure to use a high-quality sensor. In most cases non-OEM sensors are of lesser quality will not perform correctly and will cause the problem. It’s highly recommended that you stick with OEM brand replacements.