Circuit Description
The VCM supplies a voltage of approximately 0.45 volt (45 mV) between the HO2S High and the HO2S Low circuit.
Important: If the voltage is measured with a 10 megohm digital voltmeter, the voltage may read as low as 0.32 volt. 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.
When the HO2S temperature is below 360°C (600°F), the sensor will not produce any voltage. The sensor will 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 P0155 determines if the HO2S heater is functioning properly by monitoring the amount of time necessary for the HO2S to become active after start-up. This DTC is a type B DTC.
Conditions for Setting the DTC
The following conditions will set the DTC:
| • | The System Voltage is greater than 9 volts but less than 17 volts |
| • | The MAF is less than 27 grams per second for the 5.0L,5.7L |
| • | The MAF is less than 45 grams per second for the 7.4L |
| • | The Engine Coolant Temperature (ECT) is less than 32°C (90°F) |
| • | The Intake Air Temperature (IAT) is less than 32°C (90°F) |
| • | The difference between the ECT sensor and the IAT sensor is no more than 5°C (41°F) for the 5.0L, 5.7L |
| • | The difference between the ECT sensor and the IAT sensor is no more than 8°C (47°F) for the 7.4L |
| • | The time for the HO2S (Bank 2, Sensor 1) in order to obtain ±150 mV from 450 mV is too great |
Action Taken When the DTC Sets
The VCM turns the malfunction indicator lamp (MIL) ON after 2 consecutive test failures.
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 in Engine Electrical.
| • | Check for a poor connection or a damaged harness. |
| • | Inspect the harness for the following conditions: |
| - | Backed out terminals |
| - | Improper mating |
| - | Broken locks |
| - | Improperly formed or damaged terminals |
| - | A poor terminal to wire connection |
| - | A damaged harness |
Test Description
The numbers below refer to the step numbers in the diagnostic table.
-
This step determines if the DTC P0155 is the result of a hard failure or an intermittent condition. With the ignition ON and the engine off, the HO2S (Bank 2, Sensor 1) voltage displayed on the scan tool should gradually change to 0.150 volt, indicating that the heater is working properly. The HO2S voltage can rise as high as 975 mV before it toggles back down. The main thing to look for is a change.
-
Probing terminal D of the HO2S (Bank 2, Sensor 1) connector verifies if voltage is available to the HO2S (Bank 2, Sensor 1) heater.
-
If voltage is available at the connector, then it becomes a good voltage source to check for a ground at terminal C.
-
This step determines if voltage is not available at the HO2S (Bank 2, Sensor 1) due to an open fuse or open ignition feed circuit. If the fuse is open, determine if it was due to a short in the ignition feed circuit before replacing the fuse.
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 voltage displayed gradually decrease by the specified value? | 0.150 V (150 mV) | |||
Is the test lamp on? | -- | |||
Connect a test lamp between terminals C and D of the HO2S (Bank 2, Sensor 1) sensor connector. 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. Are any additional DTCs stored? | -- | Go to The Applicable DTC Table | |
6 | Check for an open in the HO2S (Bank 2, Sensor 1) sensor fuse. Is the HO2S (Bank 2, Sensor 1) fuse open? | -- | ||
7 | Check the connections at the H02S (Bank 2, Sensor 1) sensor. Was a problem found? | -- | ||
8 | Check connections at H02S (Bank 2, Sensor 1) sensor. Was a problem found? | -- | ||
9 | Check connections at H02S (Bank 2, Sensor 1). Was a problem found? | -- | ||
10 | Repair the open HO2S (Bank 2, Sensor 1) sensor ground circuit. Refer to Wiring Repairs in Engine Electrical. Is the action complete? | -- | -- | |
11 | Check for an open at the HO2S (Bank 2, Sensor 1) sensor ignition feed circuit. Was a problem found? | -- | -- | |
12 | Repair the faulty connection. Refer to Wiring Repairs in Engine Electrical. Is the action complete? | -- | -- | |
13 | Repair the open in the HO2S (Bank 2, Sensor 1) sensor ignition feed circuit. Refer to Wiring Repairs in Engine Electrical. Is the action complete? | -- | -- | |
14 | Repair the short to ground in the HO2S (Bank 2, Sensor 1) sensor ignition feed circuit and replace fuse. Refer to Wiring Repairs in Engine Electrical. Is the action complete? | -- | -- | |
15 | Replace the HO2S (Bank 2, Sensor 1) sensor. Refer to Heated Oxygen Sensor (HO2S) Replacement . Is the action complete? | -- | -- | |
16 |
Does the scan tool indicate that this diagnostic ran and passed? | -- | ||
17 | Using the scan tool, select the Capture Info and the Review Info. Are any DTCs displayed that have not been diagnosed? | -- | Go to The Applicable DTC Table | System OK |
