Circuit Description
This diagnostic test is used to determine if the heating element in the post-converter oxygen sensor is operating properly. An oxygen sensor acts as a battery because it creates its own voltage once it reaches operating temperature. This voltage is produced when the oxygen content in the exhaust stream is different than that in the atmosphere. The heating element is energized through CKT 139 when the ignition is ON and allows the oxygen sensor to reach operating temperature quickly. This in turn allows the PCM to enter Closed Loop fuel control quicker. When cold the voltage that the PCM measures on the HO2S HI and LOW inputs is called bias voltage. If it takes too long for the HO2S to vary above or below the bias voltage within a specific time since key ON DTC P0147 will set
Conditions for Setting the DTC
Test Conditions
| • | DTCs P0101, P0102, P0103, P0117, P0118 and P0146 not set. |
| • | Engine coolant temperature dropped at least 10°C (50°F) from the end of the last ignition cycle to the beginning of this ignition cycle. |
| • | Average post-converter heated oxygen sensor bias voltage between 352 millivolts and 546 millivolts. |
| • | Engine did not stall during test. |
Failure Condition
The PCM monitors the post-converter heated oxygen sensor input to determine when its voltage becomes either 151 millivolts less than or 151 millivolts greater than average post-converter heated oxygen sensor bias voltage for 0.1 seconds. If it takes too long, DTC P0147 will set.
Action Taken When the DTC Sets
| • | The PCM will illuminate the Malfunction Indicator Lamp (MIL) after two consecutive drive trips that the diagnostic runs and fails. |
| • | The PCM will record operating conditions at the time the DTC sets. This information will be stored in the Freeze Frame and Failure Records. |
| • | A first failure of this DTC will store in Last Test Failed but not History. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn the MIL OFF after three consecutive drive trips that the diagnostic runs and does not fail. |
| • | A Last Test Failed DTC will clear when the diagnostic runs and does not fail. |
| • | A History DTC will clear after forty consecutive warm-up cycles with no failures of any diagnostic test. |
| • | Use a scan tool to clear DTCs. |
| • | Interrupting PCM battery voltage may or may not clear DTCs. This practice is not recommended. Refer to Clearing Diagnostic Trouble Codes in PCM Description and Operation. |
Diagnostic Aids
Notice: Do not solder heated oxygen sensor wires. Soldering the wires will result in the loss of the air reference to the sensor. Refer to Engine Electrical for proper wire and connection repair techniques.
An intermittent open in CKT 139 or 250 may cause DTC P0147 to set. Additionally, a malfunctioning post-converter oxygen sensor heater may be the cause.
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
-
Checking for proper voltage to oxygen sensor heater.
-
When starting with a cool sensor, amperage should start at 1.5 amps and slowly drop to about 0.9 amps. This verifys that the heater is actually producing heat.
-
Checking if fault is present.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to A Powertrain On Board Diagnostic (OBD) System Check | |
Is the voltage more than the value specified? | 10.5 volts | |||
Is the amperage between the values specified? | 0.9 - 1.5 amps | |||
4 | Measure the voltage from terminal D (harness side) to ground. Is the voltage the same or higher than the value specified? | 10.5 volts | ||
Using Freeze Frame data, operate the vehicle under the same conditions under which the DTC set. Does the DTC reset? | -- | Fault not present. Refer to Diagnostic Aids | ||
6 | Repair the open in the Post HO2S ground circuit. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- |
7 | Repair the open or short to ground (blown fuse) in the Post HO2S Ignition feed circuit. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- |
8 | Replace the oxygen sensor. Refer to Heated Oxygen Sensor (HO2S) Replacement (Pre- and Post-Converter) . Is the replacement complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- |
