Powertrain Controls - ECM/PCM

DTC 42 Chart:

Heated Oxygen Sensor Circuit:

CIRCUIT DESCRIPTION
The PCM provides a reference signal of 0.45 volt to the HO2S on CKT 412. When the HO2S is cold, below 200°C (392°F), the HO2S signal voltage will be around 0.45 volts and the PCM will keep the system in "Open Loop" operation. When the HO2S is warm, above 2OO°C (392°), the HO2S will swing from rich to lean rapidly, at least one swing every two seconds if the PCM is in good control of the air fuel mixture. DTC 42 is designed so that if the HO2S stays at a lean voltage for more than 50.3 seconds during the test conditions, DTC 42 will be set.

DTC 42 WILL SET WHEN
- DTCs 14, 15, 16, 21, 22, 26, 27, 31, 32, 34 and 119.
- Throttle switch open.
- TP angle between 5.4° and 25°.
- Coolant temperature above 82.5°C (180.5°F).
- Engine speed 800 RPM or greater are not set.
- Traction control not active.
- The Bank 2 HO2S voltage is below 0.3 volt for more than 50.3 seconds.
- MAP greater than 20.2 kPa.

ACTION TAKEN (PCM WILL DEFAULT TO)
- With current DTC 42 set, the PCM will illuminate the Malfunction Indicator Lamp (MIL) (Service Engine Soon).
- PCM enables evaporative emission control solenoid if DTC 44 is also set.

DTC 42 WILL CLEAR WHEN
The fault no longer exists and ignition is cycled "OFF" and "ON."

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. If DTC 17 is also set, diagnose it first because an oxygen sensor not ready can cause other emission related problems.
2. If the oxygen sensor is operating correctly, voltage will fluctuate above 0.3 volt. A lean sensor/condition will cause the voltage to remain below 0.3 volt.
3. If greater than 0.15 volt is measured, the PCM and CKT 412 are OK.

DIAGNOSTIC AIDS
Using the Tech 1 scan tool, observe the long term fuel trim at different RPM and air flow conditions. The Tech 1 scan tool 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 42 may have been set. If the conditions for DTC 42 exist, the long term fuel trim values will be around 150.

HO2S wire
Sensor pigtail may be mispositioned and contacting the exhaust manifold. Check for intermittent ground in wire between connector and sensor.

Lean injector(s)
Perform "Injector Balance Test," Chart C-2A. Chart C-2A Injector Coil Balance Test Procedure

Fuel contamination
Water, even in small amounts, near the in-tank fuel pump inlet can be delivered to the injectors. The water causes a lean HO2S signal and can set a DTC 42.

Fuel pressure
System will be lean if pressure is too low. It may be necessary to monitor fuel pressure while driving the car at various road speeds and/or loads to confirm. Refer to "Fuel System Diagnosis," Chart A-7. Chart A-7 Fuel System Pressure Test

Exhaust leaks
If there is an exhaust leak, the engine can cause outside air to be pulled into the exhaust and past the sensor. Vacuum or crankcase leaks can cause a lean condition.

If the above are OK, it is a faulty Heated Oxygen Sensor (HO2S).