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DTC 522739 Oxygen Sensor Short/Open
Conditions for Setting the DTC
The maximum current, current to ground, and drain voltage are monitored internally to the ECU. If the cur-
rent at the driver chip goes above 3 amps, current to ground goes above 100 micro Amps, or voltage drops
below 3 volts, a diagnostic code will be set.
Circuit Description
The system monitors the O2 sensor to ensure that the fuel control is functioning properly. The HEGO sen-
sor is mounted in the exhaust system downstream of the engine. It is used to measure 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 mix-
ture 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 condition, the ECM will set a di-
agnostic code and turn on the MIL light in the dash. The O2 sensor uses a heater circuit to bring it up to
operating temperature as quickly as possible, as well as maintaining the temperature during idle. The hea-
ter is controlled by the ECU, which will cycle the heater to prevent overheating of the sensor
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