P0137

DTC P0137 HO2S Circuit Low Voltage (Bank 1, Sensor 2) (Catalyst Motor):

Heated Oxygen Sensor (HO2S) (Bank 1, Sensor 2):

CIRCUIT DESCRIPTION
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-A (VCM-A) has the capability to monitor this process using Heated Oxygen Sensor (HO2S) 2. HO2S 2, located in the exhaust stream past the three-way 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. 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 monitor an excessively low HO2S 2 signal voltage for an extended period of time, the VCM-A will set DTC P0137, indicating a possible short to ground in CKT 1670. DTC P0137 determines if the HO2S or circuit is shorted to low by checking for a lean condition during steady throttle and power enrichment.

DTC PO137 WILL SET WHEN
^ No Throttle Position (TP) sensor DTCs.
^ No Evaporative Emissions (EVAP) System DTCs.
^ No Intake Air Temperature (IAT) sensor DTCs.
^ No Manifold Absolute Pressure (MAP) DTCs.
^ No Exhaust Gas Recirculation (EGR) DTCs.
^ No fuel trim DTCs.
^ No Engine Coolant Temperature (ECT) sensor DTCs.
^ "Closed Loop."
^ Air/fuel ratio is between 14.5% and 14.8%.
^ Throttle position is between 5% and 50%.
^ Above met for 5 seconds.
^ HO2S voltage is less than 0.26 volt.

ACTION TAKEN (VCM-A WILL DEFAULT TO)
The VCM-A will turn "ON" the Malfunction Indicator Lamp (MIL) (Service Engine Soon) after 2 consecutive failures.

DTC PO137 WILL CLEAR WHEN
The VCM-A will turn the MIL "OFF" after three consecutive trips without a fault condition present. A history DTC will be cleared if no fault conditions have been detected for forty warm-up cycles [coolant temperature has risen 22°C (40°F) from start-up coolant temperature and engine coolant temperature exceeds 71°C (160°F) that same ignition cycle] or the Tech 1 clearing feature has been used.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. Determines if conditions necessary for setting DTC P0137 exist.
2. Opening CKT 1671 and completing CKT 1670 to ground should cause the Tech 1 to display the VCM-A-supplied bias voltage (0.35 - 0.55 volt). If the signal voltage is still low, CKT 1671 is shorted to ground or the VCM-A is faulty.

DIAGNOSTIC AIDS
An intermittent may be caused by rubbed through wire insulation or a wire contacting the exhaust.

Check for:
^ Poor connection or damaged harness - Inspect harness for short to ground in CKT 1671, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.
^ Intermittent test - Observe HO2S 2 on Tech 1 while moving related connectors and wiring harness with the key "ON." If the failure is induced, the HO2S 2 display will change. This may help isolate the location of the malfunction. If OK, replace faulty HO2S.