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DTC 522636 Short Term Fuel Lean, Bank 1
Conditions for Setting the DTC
The short term fuel correction has a range of ± 25%. If the correction reaches the upper or lower limit, it will
then try an additional 2% change to watch for an O2 switch. If the sensor switches with the additional 2%, a
short term fuel correction code will be set. If the sensor does not switch with the additional 2% change, the
system will set a code for a sensor that fails to switch rich or lean.
Circuit Description
The system monitors the O2 sensor to ensure that the fuel control is functioning properly. The HEGO
sensor is mounted in the exhaust system downstream of the engine. The HEGO sensor is used to meas-
ure the amount of oxygen present in the exhaust stream and communicates that to the ECM via an
electrical signal. The amount of oxygen present in the exhaust stream indicates whether the fuel air ratio is
rich or lean. If the HEGO sensor signal indicates that the exhaust stream is rich, the ECM will decrease or
lean the fuel mixture by reducing the short term fuel correction value which reduces the injector on-time
supplying less fuel. If the mixture is lean, the ECM will richen the mixture or increase the short term fuel
correction value which will increase the pulse width to the injectors. Under normal steady operation the
short term fuel correction value should move up and down approx. 5%. This 5% movement may range
within a plus 25 to minus 25 percent window. The ECM continuously monitors the HEGO sensor output. If
a rich or lean condition is present for an extended period of time and if the ECM cannot correct the condi-
tion, the ECM will set a diagnostic code and turn on the MIL light in the dash. NOTE: The HEGO sensor is
sensitive to silicone and silicone-based products and can become contaminated. Avoid using silicone sea-
lers or hoses treated with silicone lubricant in the air stream or fuel supply lines.
Diagnostic Aids
Low fuel pressure
Partially blocked fuel injectors
Manifold vacuum leaks
Defective O2 sensor
A misfire on one or more cylinders
Exhaust leak ahead of the O2 sensor
Faulty MAP sensor
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