Circuit Description
The VCM supplies a voltage of about 0.45V (450 mV) between the HO2S High and the HO2S Low circuits. (If measured with a 10 megohm digital voltmeter, this may read as low as 0.32V.) The HO2S varies the voltage within a range of between about 1.0V (1000 mV) if the exhaust is rich, to about 0.10V (100 mV) if the exhaust is lean.
The sensor is like an open circuit and produces no voltage when it is below about 360°C (600°F). DTC P0158, P0158 or an open sensor circuit or cold sensor causes Open Loop operation. P0152 determines if the HO2S or circuit is shorted to high by checking for a rich condition during steady throttle. DTC P0158 is a type A DTC.
Conditions for Setting the DTC
| • | No TP sensor DTCs |
| • | No EVAP DTCs |
| • | No IAT sensor DTCs |
| • | No MAP sensor DTCs |
| • | No ECT sensor DTCs |
| • | No MAF sensor DTCs |
| • | No intrusive test in progress |
| • | No device controls active |
| • | System voltage is at least 9 V |
Test Enable Rich Test
| • | Closed Loop |
| • | Air/fuel ratio is at least 14.5 but less than 14.8 |
| • | TP is greater than 5% but less than 99% |
| • | Above met for 5 seconds |
| • | Related HO2 sensor DTCs not active since code clear |
Test Enable Decel Fuel Cut Off (DFCO) Rich Test
| • | Decel Fuel cutoff mode active |
| • | Closed Loop |
| • | Time elapsed is at least 2 seconds |
| • | Related HO2 sensor DTCs not active since code clear |
Action Taken When the DTC Sets
A current DTC P0158 will cause the system to operate in Open Loop. With a current DTC P0158 set, the MIL (Malfunction Indicator Lamp) will be illuminated after 1 test failure.
Conditions for Clearing the MIL/DTC
The VCM turns OFF the MIL after 3 consecutive driving trips without a fault condition present. A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (the coolant temperature has risen 22°C (40°F) from the start-up coolant temperature and the engine coolant temperature exceeds 71°C (160°F) during that same ignition cycle) or the scan tool clearing feature has been used.
Diagnostic Aids
Check the following items
| • | Fuel pressure. System will go rich if pressure is too high. The VCM can compensate for some increase. However, if it gets too high, DTC P0158 may be set. Refer to Fuel System Diagnosis . |
| • | Rich injector. Perform the Fuel Injector Balance Test for the 5.7L or the 7.4L. |
| • | Check for fuel contaminated oil. |
| • | EVAP canister purge. Check for fuel saturation. If full of fuel, check canister control and hoses. Refer to Evaporative Emission Control System Diagnosis . |
| • | Check for leaking fuel pressure regulator diaphragm by checking vacuum line to regulator for fuel. |
| • | TP sensor. An intermittent TP sensor output will cause the system to go rich due to a false indication of the throttle moving. |
| • | False rich indication due to silicon contamination of the HO2S. This will be indicated by DTC P0158 accompanied by lean driveability conditions and a powdery white deposit on the sensor. |
| • | Faulty HO2S (Bank 2 Sensor 2). If HO2S (Bank 2 Sensor 2) is internally shorted the HO2S (Bank 2 Sensor 2) voltage displayed on a scan tool will be over 1 V. Try disconnecting the HO2S (Bank 2 Sensor 2); if the displayed voltage goes from over 1000 mV to around 450 mV, replace HO2S (Bank 2 Sensor 2). |
| • | Never solder the HO2S wires. |
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
|
Important: Before clearing DTC(s) use the scan tool to record Freeze Frame and Failure Records for reference, as data will be lost when the Clear Info function is used. Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | |||
2 |
Does the scan tool data display indicate HO2S (Bank 2 Sensor 1) voltage fixed above the specified value? | 1200 RPM 5.0L ,7.4L - 0.976V (976 mV) 5.7L - 0.993V (993 mV) | ||
3 |
Does the scan tool data display indicate HO2S (Bank 2 Sensor 2) voltage is below the specified value? | 0.20V (200 mV) | ||
4 | The DTC is intermittent. If no additional DTCs are stored, refer to Diagnostic Aids. If additional DTCs are stored refer to those Table(s). Are any additional DTCs stored? | -- | Go to the Applicable DTC Table | |
5 | Refer to Diagnostic Aids. | -- | -- | -- |
6 | Replace the VCM. Important: If the VCM is faulty, the new VCM must be programmed. Refer to VCM Replacement/Programming . Is the action complete? | -- | -- | |
7 |
Does the scan tool indicate that this diagnostic Ran and Passed? | -- | ||
8 | Using the scan tool, select Capture Info, Review Info. Are any additional DTCs displayed that have not been diagnosed? | -- | Go to the Applicable DTC Table | System OK |
