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 about 0.45 volt (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 sensor is like an open circuit and produces no voltage when it is below 360°C (600°F).
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 P0140 determines if the HO2S or the HO2S circuit has developed an open. 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 Open Test Enable
| • | A Closed Loop |
| • | The DTC P0141 (HO2S heater) not set |
| • | HO2S voltage greater than 0.299 volts but less than 0.598 volts. |
| • | Engine run time is greater than 2 minutes |
| • | HO2S (Bank1, Sensor 2) voltage is greater than 299 mV but less than 598 mV |
Action Taken When the DTC Sets
The VCM turns the malfunction indicator lamp (MIL) ON after 2 consecutive test failures.
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 listed below refer to the step numbers on the diagnostic table.
-
If the conditions for the setting DTC P0140 exist, the system will not go into a Closed Loop.
-
This step determines if the sensor or the wiring is the cause of the DTC P0140.
-
This test checks the continuity of the HO2S 2 High signal circuit.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 |
Important: Before clearing DTCs, use the scan tool in order to record freeze frame and the failure records for reference because the Clear Info function will lose the data. 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 the HO2S (Bank 1, Sensor 2) voltage less than the specified value? | 0.2 V (200 mV) | |||
Is the test lamp ON? | -- | |||
5 | The DTC is intermittent. If no additional DTCs are stored, refer to the Diagnostic Aids. If additional DTCs are stored, refer to those tables. | -- | Go to The Applicable DTC Table | |
6 | Check for an open in the HO2S (Bank 1, Sensor 2) signal circuit. Was a problem found? | -- | ||
7 | Check for a faulty HO2S (Bank 1, Sensor 2) connection. Was a problem found? | -- | ||
8 | Check for a poor connection at the VCM. Was a problem found? | -- | ||
9 | Repair the open HO2S (Bank 1, Sensor 2) ground circuit. Refer to Wiring Repairs in Engine Electrical. Is the repair complete? | -- | -- | |
10 | Replace the HO2S (Bank 1, Sensor 2). Refer to Heated Oxygen Sensor (HO2S) Replacement . Is the replacement complete? | -- | -- | |
11 | Repair the circuit as necessary. Refer to Wiring Repairs in Engine Electrical. Is the repair complete? | -- | ||
12 | Replace the VCM. Important: If the VCM is faulty, reprogram the VCM. Refer to VCM Replacement/Programming . Is the replacement complete? | -- | -- | |
13 |
Does the scan tool indicate that this diagnostic ran and passed? | -- | ||
14 | Using the scan tool, select the Capture Info and the Review Info. Are any DTCs displayed that have not been diagnosed? Using the scan tool | -- | Go to The Applicable DTC Table | System OK |
