Rick's Free Auto Repair Advice

Posts Tagged: oxygen sensor

check engine light on Part 2

How to diagnose a check engine light Part 2 If you read part one of this check engine light on series, you already know that the first step in finding the cause of a check engine light on is to read the trouble codes. But then what? How do you interpret them and avoid replacing good parts? First, understand that vehicle computers NEVER tell you the root cause of the problem. They only tell you which sensors are providing readings that are outside of expected boundaries. Sure, the sensor could … Read More

Overheated catalytic converter

How a catalytic converter works

How a catalytic converter works, what it does A catalytic converter converts the various exhaust compounds of hardrocarbons (HC), Oxygen (O2), and Oxides of Nitrogen (N2) into more environmentally friendly gases. If a perfect world, all engines would burn the perfect combination of air and fuel in this ratio: 14.7:1 (air to fuel). After combustion, you would wind up with CO2, H2O and N2. Unfortunately, that never happens in the real world. How your car actually computes the air fuel mixture You’re constantly adjusting the gas pedal and the car … Read More


Fix code P2098 trouble code on Dodge Stratus, Sebring Trouble code P2098 on a Dodge Sebring or Dodge Stratus indicates that the downstream (post catalytic converter) is reporting a reading that’s consistently above or below center for a predetermined amount of time. Most DIYers replace the oxygen sensor and wonder why they still get the same code. In effect they’re treating the messenger and not the message. An exhaust system has two oxygen sensors. The first sensor tests how well the computer did in calculating air/fuel mixture. The second sensor … Read More


Fix code P0137 Oxygen Sensor Circuit Low Voltage (Bank 1 Sensor 1). This sensor is located on the engine bank that houses #1 cylinder and is located AFTER the catalytic converter The PCM sends a reference voltage (usually 5-volts) to the variable resistor in the oxygen sensor and looks for a return voltage. Once the sensor is heated up, the PCM expects to see a varying voltage. If the PCM sees a constant low voltage, it will set a trouble code P0137. Most common causes are: vacuum leak that’s allowing … Read More

P2237 P2238 P2240 P2241 Avalon Camry

Fix code P2237 P2238 P2240 P2241 on Toyota Avalon and Toyota Camry Toyota has issued a technical service bulletin (TSB) 0278-08 to address trouble codes P2237, P2238, P2240, P2241 on 2008 Toyota Avalon and 2008-09 Toyota Camry (with 2GR-FE and 2AZ-FE engines). P2237 Oxygen (A/F) Sensor Pumping Circuit Low (Bank 1 Sensor 1) P2238 Oxygen (A/F) Sensor Pumping Circuit Open (Bank 1 Sensor 1) P2240 Oxygen (A/F) Sensor Pumping Circuit Low (Bank 2 Sensor 1) P2241 Oxygen (A/F) Sensor Pumping Circuit Open (Bank 2 Sensor 1) Do NOT start replacing … Read More

OBDII trouble Codes

OBDII trouble Codes I can’t tell you how many times forum members write in and say, “The computer said to replace the oxygen sensor. I replaced it and now it says to replace it again.” Let’s get one thing straight…..the computer NEVER says to replace a part. It only tell you what condition the OBDII trouble Codes. Here’s a typical example: P0137 – Oxygen Sensor Circuit Low Voltage (Bank 1 Sensor 2) Now most of you would say the computer has determined that the oxygen sensor is bad. That’s NOT … Read More

P0420 Catalyst System Efficiency

P0420 Catalyst System Efficiency Below Threshold (Bank 1) This code means the catalytic converter that treats the exhaust for Bank 1 has failed it’s testing. The oxygen sensor in front of the catalytic converter switches back and forth between rich and lean as the computer constantly changes air fuel mixture. But after the exhaust leaves the converter, the next oxygen sensor should not switch between rich and lean. If it does, that means the catalytic converter is NOT doing its job. Catalytic converters generally do NOT fail on their own. … Read More


P0133 – Oxygen Sensor Circuit Slow Response (Bank 1 Sensor 1) A P0133 trouble code means the oxygen sensor response doesn’t meet proper criteria. An Oxygen sensor must switch constantly between .27 and .62 volts. The engine computer waits until the engine has reached at least 145 degrees and the vehicle has driven at least 10MPH for 30 seconds before it starts looking at the switching rate. The computer looks for about 8 voltage changes per second (these are called CROSS COUNTS). If it sees less than that, it sets … Read More

Replace O2 Sensor

How to replace an O2 sensor Most people automatically assume an O2 sensor trouble code means they should replace the oxygen sensor. They immediately want to know how to replace an oxygen sensor. However, if you jump to that conclusion without actually testing the sensor, you could be wasting your money. Take a minute to understand how an O2 sensor works and how they go bad. What causes an O2 sensor trouble code? Oxygen sensor trouble codes start with P0130 and go up to P0167. Newer style air/fuel ratio sensors … Read More

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