S15/T15 Jimmy 2WD V6-262 4.3L VIN W CPI (1995)
Oxygen Sensor: Testing and Inspection
With Vehicle Control Module (VCM-A)
Heated Oxygen Sensor (HO2S 1)
The Heated Oxygen Sensor (HO2S 1) is mounted in the exhaust before the catalytic converter where it can monitor the oxygen content of the
exhaust gas stream.
The oxygen content in the exhaust reacts with the sensor to produce voltage output. This voltage should constantly fluctuate from approximately
100 mV (high oxygen content lean mixture) to 900 mV (low oxygen content rich mixture). The heated oxygen sensor voltage can be monitored
with a Tech 1.
By monitoring the voltage output of the heated oxygen sensor, the Vehicle Control Module (VCM-A) calculates what fuel mixture command to
give to the injector (lean mixture-low HO2S 1 voltage=rich command, rich mixture-high HO2S 1 voltage=lean command).
The heated oxygen sensor circuit, if open, should set a Diagnostic Trouble Code (DTC) P0134 and the Tech 1 will display a constant voltage
between 350 - 550 mV. A constant voltage below 250 mV in the sensor circuit should set DTC PO131, while a constant voltage above 950 mV in
the circuit should set DTC PO132. DTC P0131 and DTC P0132 could also he set as a result of fuel system problems. Refer to DTC charts for
conditions that can cause a lean or rich system. Refer to Diagnostic Trouble Code Charts. Under Computer and Controls/System
Diagnosis/Procedures. See: Testing and Inspection
Heated Oxygen Sensor (HO2S 2) Catalyst Monitor
In order to control emissions of Hydrocarbons (HC), Carbon Monoxide (CO) and Oxides of Nitrogen (NOx), a three-way catalytic converter is
used. The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas, converting them
into harmless water vapor and carbon dioxide. The catalyst also reduces NOx, converting it to nitrogen. The Vehicle Control Module (VCM-A)
has the capability to monitor this process using Heated Oxygen Sensor (HO2S) 2. HO2S 2, located in the exhaust stream past the catalytic
converter, produces an output signal which indicates the oxygen storage capacity of the catalyst; this in turn indicates the catalyst's ability to
convert exhaust emissions effectively. A problem with the HO2S 2 electrical circuits should set Diagnostic Trouble Code (DTC) P0137, PO138 or
PO14O, depending on the specific condition. If the catalyst is functioning correctly, the HO2S 2 signal will be far less active than that produced by
HO2S 1. If a problem exists which causes the VCM-A to detect excessive HO2S 2 activity outside of an acceptable range for an extended period
of time, the VCM-A will set DTC P0420, indicating that the catalytic converter's oxygen storage capacity is below a threshold considered
acceptable. Refer to Diagnostic Trouble Code Charts. Under Computer and Controls/System Diagnosis/Procedures. See: Testing and
Inspection
