Powertrain Controls - ECM/PCM

Diagnostic Trouble Code (DTC) 45:

Left Oxygen Sensor Circuit:

CIRCUIT DESCRIPTION
The Powertrain Control Module (PCM) supplies a voltage of about 450 mV between terminals "C20" and "C19" (If measured with a 10 megohm digital voltmeter, this may read as low as 320 mV.). The Heated Oxygen Sensor (HO2S) varies the voltage within a range of about 1000 mV if the exhaust is rich down through about 10 mV if exhaust is lean.

The sensor is like an open circuit and produces no voltage when it is below 315°C (600°F). An open sensor circuit or cold sensor causes "Open Loop" operation. Whenever the ignition is "ON" voltage is supplied to the HO2S heaters on CKT 439. Even with the engine not running, the HO2S will reach operating temperature and indicate the oxygen content of the exhaust gas at the sensor. Typically the signal voltage will be near 450 mV at key-up. The signal voltage will then rise or drop as the sensor becomes active, depending on the oxygen content of the air near the sensor.

DIAGNOSTIC TROUBLE CODE (DTC) 45 WILL SET WHEN
System is operating in "Closed Loop," not in power enrichment, signal voltage remaining above 700 mV for 50 seconds and throttle angle is greater than 5%.

ACTION TAKEN (PCM DEFAULT)
The Malfunction Indicator Lamp (MIL) will illuminate and the fuel control system will go into "Open Loop."

DTC CHART TEST DESCRIPTION
Number below refers to the circled number on the diagnostic chart.

1. Engine must be at normal operating temperature before performing this test.

DIAGNOSTIC AIDS
Using the Tech 1 Scanner, observe the long term fuel trim values at different RPM and load conditions. The Tech 1 also displays the fuel trim cells, so the long term fuel trim values can be checked in each of the cells to determine when the DTC 45 may have been set. If the conditions for DTC 45 exist, the long term fuel trim values will be near 108.

^ Fuel pressure. System will go rich if pressure is too high. The PCM can compensate for some increase. However, if it gets too high, a DTC 45 may be set. Refer to Chart A-7 Fuel System Diagnosis. Related Tests, Information and Procedures

^ Rich injector. Refer to Chart C-2A Injector Coil Test Procedure or use Tech 1 scanner. Chart C-2A Injector Coil Test Procedure

^ Leaking injector. Refer to Chart A-7 Fuel System Diagnosis. Related Tests, Information and Procedures

^ Check for fuel contaminated oil.

^ Evaporative Emission (EVAP) canister pure. Check for fuel saturation. If full of fuel, check canister control and hoses. Refer to Chart C-3 EVAP Cannister Purge Solenoid Check. Chart C-3 EVAP Canister Purge Solenoid Check

^ Mass Air Flow (MAF) sensor. Disconnect the MAF sensor and see if rich condition is corrected. If so, check for proper installation. If installed OK, replace MAF sensor. If the MAF sensor is installed backwards, the system will go rich. The plastic portion of the sensor has arrows cast into it indicating proper air flow direction. The arrows must point toward the engine.

^ Check for leaking fuel pressure regulator diaphragm by checking vacuum line to regulator for fuel.

^ Throttle Position (TP) sensor. An intermittent TP sensor output will cause the system to go rich, due to a false indication of the engine accelerating.

^ Exhaust Gas Recirculation (EGR). An EGR valve staying open (especially at idle) will cause the oxygen sensor to indicate a rich exhaust, and this could result in a DTC 45.

^ Heated oxygen sensor. All HO2S wires and connections should be inspected for breaks or contamination that could prevent reference voltage from reaching the H02S.