Circuit Description
Important: If the voltage is measured with a 10 megohm digital voltmeter, the voltage may read as low as 0.32 volt.
The VCM supplies a voltage of approximately 0.45 volts (450 mV) between the HO2S High and the HO2S Low circuits. The Heated Oxygen Sensor (HO2S) varies the voltage from approximately 1.0 volt (1000 mV) during rich conditions to 0.10 volt (100 mV) during lean conditions.
The VCM monitors the Heated Oxygen Sensor (HO2S) activity for 100 seconds after a Closed Loop. During the monitor period, the VCM counts the number of times that the HO2S switches from rich to lean and from lean to rich and adds the amount of time it took to complete all switches. With this information, an average time for all of the switches can be determined. If the average time to switch is too slow, a DTC P0146 sets.
When the HO2S temperature is below 360°C (600°F), the sensor will not produce any voltage. The sensor will also behave like an open circuit. This will result in an Open Loop operation.
The HO2S heater provides for a faster sensor warm-up which allows the sensor to become active in a shorter period of time and remain active during a long extended idle. The DTC P0146 determines if the HO2S is functioning properly by checking the response time of the sensor. This is a type B DTC.
Conditions for Setting the DTC
The following conditions will set 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 |
| • | The system voltage measures at least 9.0 volts |
| • | The engine run time is greater than 2 minutes |
| • | The HO2S voltage is greater than 0.299 volts (299 mV), and less than 0.598 volt (598 mV). For the 7.4L the HO2S voltage is greater than 0.399 volts (399 mV), and less than 0.468 volts (468 mV) |
HO2S Sensor Temperature Test
- Not in DFCO
- ECT is greater than or equal to 80°C.
- The air flow is greater than or equal to 15 grams per second.
HO2S Sensor Open Test Enable
| • | The HO2S Sensor Temperature test equals true |
| • | The engine run time is greater than 2 minutes. |
| • | The DTC P0147 in not active. |
| • | A Closed Loop exists. |
Action Taken When DTC Sets
The VCM turns the MIL ON after the second 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
Important: Never solder the HO2S wires. For proper wire and connection repairs, refer to Wiring Repairs.
A intermittent may be caused by a poor connection, a rubbed through wire insulation, or a broken wire inside the insulation.
Check for the following conditions:
| • | A poor connection or a damaged harness: Inspect the harness connectors for the following conditions: |
| - | Backed out terminals |
| - | Improperly formed or damaged terminals |
| - | Poor terminal to wire connection |
| - | Damaged harness |
| • | A malfunctioning HO2S heater or heater circuit: With the ignition ON and the engine OFF, the HO2S voltage displayed on a scan tool should gradually drop to below 0.150 volt, indicating that the heater works properly. If not, disconnect the HO2S and connect a test lamp between the terminals C and D. If the test lamp does not light, repair the open in the HO2S ground circuit or the HO2S ignition feed circuit. If the test lamp lights, replace the HO2S. |
| • | The Intermittent test: Use a scan tool in order to monitor this HO2S signal voltage. Move the related connectors and the wiring harness with a warm engine running at part throttle in Closed Loop. If the failure is induced, the HO2S signal voltage reading changes from its normal fluctuating voltage (above 600 mV and below 300 mV) to a fixed value around 450 mV. This may help to isolate the location of the malfunction. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
If the conditions for setting this DTC exist, the system will not go into a Closed Loop.
-
This test checks the continuity of the HO2S signal circuit.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 |
Important: Before clearing the DTCs, use the scan tool in order to record the Freeze Frame and the Failure Records for reference. This data will be lost when the Clear DTC Information function is used. Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||
Does the scan tool indicate a Closed Loop? | 1200 RPM | |||
Does the scan tool data display indicate a HO2S voltage less than the specified value? | 0.2 V (200 mV) | |||
4 |
Is the voltage near the specified value? | 12.0V | ||
5 | This DTC is intermittent. Are any additional DTCs stored? | -- | Go to the applicable DTC table | Go to Diagnostic Aids |
6 | Check for an open in the HO2S signal circuit. Was a problem found? | -- | ||
7 | Check for a faulty HO2S connection. Was a problem found? | -- | ||
8 | Check for a poor connection at the VCM. Was a problem found? | -- | ||
9 | Repair the open HO2S ground circuit. Refer to Wiring Repairs in Electrical Diagnosis. Is the action complete? | -- | -- | |
10 | Replace the HO2S. Refer to Heated Oxygen Sensor (HO2S) Replacement . Is the action complete? | -- | -- | |
11 | Repair the circuit as necessary. Refer to Wiring Repairs in Electrical Diagnosis. Is the action complete? | -- | -- | |
12 | Replace the VCM. Important: When replacing the VCM, the new VCM will need to be programmed. Refer to VCM Replacement/Programming . Is the action complete? | -- | -- | |
13 |
Does the scan tool indicate that this diagnostic ran and passed? | -- | ||
14 | Use the scan tool in order to display the Capture Info and the Review Capture Info functions. Are there any DTCs displayed that have not been diagnosed? | -- | Go to the applicable DTC table | System OK |
