Oxygen Sensor Wiring Repairs

Exhaust Gas Sensors

• Because most oxygen sensors operate on less than one volt, special harness repair procedures must be followed. 
• The slightest poor connection will have a voltage drop across it. 
• • This voltage drop takes away voltage from the original signal being monitored by the engine computer. 
  • This can cause inaccurate readings and incorrect amounts fuel delivered to the cylinders. 
  • This can result in poor fuel economy, poor performance, or both.
• Repairs of oxygen sensor wiring are allowed as long as the repair is in the main vehicle harness.  The pigtail wires attached to the sensor are not allowed to be repaired.
• Always solder any wiring repairs.

There are two types of exhaust gas sensors:

• Oxygen Content Sensor - A four-wire Heated Exhaust Gas Oxygen Sensor (HEGO) measures the oxygen content of the exhaust gas. This sensor's output signal is used to indicate a lean or rich condition when compared to stoichiometric (14.7: air-fuel ratio) . An oxygen sensor is a unique sensor because it actually produces its own variable voltage signal.
• • When the oxygen content is low (typically indicating a rich condition), the sensor output voltage is high.
  • When the oxygen content is high (typically indicating a lean condition), the sensor output voltage is low.

• Air-Fuel Ratio Sensor - This five-wire sensor's output signal is an indication of the engine's air-fuel ratio. Normal output voltage at an idle is around 2.3 volts and can fluctuate anywhere from 0 volts to 5 volts. When a brake booster vacuum hose was removed from a test vehicle, the voltage increased to around 3.0 volts. When the air intake was restricted, the voltage dropped to around 1.6 volts. This type of sensor is very fast to react and can be used to monitor the actual air-fuel ratio of each cylinder's exhaust pulses. This information can then be used to modify the air-fuel ratio per cylinder to optimize emissions and fuel economy. This sensor is also called a Universal Exhaust Gas Oxygen (UEGO) Sensor, a Linear Oxygen Sensor, or a Wide Band Oxygen Sensor.
• • When the air-fuel ratio is rich, the sensor output voltage trends lower.
  • When the air-fuel ratio is lean, the sensor output voltage trends higher