Circuit Description
The PCM provides a 0.45 volt reference signal to the oxygen sensor on CKT 1668. When the oxygen sensor is cold, below 200°C (392°F), the Oxygen Sensor signal voltage will be around 0.45 volt and the PCM will keep the system in Open Loop operation. When the oxygen sensor is warm, above 200°C (392°F), the oxygen sensor will swing from rich to lean rapidly, if the PCM is in good control of the air fuel mixture. DTC P0143 is designed so that if the oxygen sensor stays at a lean voltage for 100 out of 120 seconds during the test conditions, this DTC will set. DTC P0143 will set when:
| • | There is an oxygen sensor circuit fault giving a false lean indication. |
| • | The air fuel ratio is actually lean due to a vacuum leak or fuel control system fault. |
Conditions for Setting the DTC
Test Conditions
| • | DTCs P0101, P0102, P0103, P0107, P0108, P0117, P0118, P0121, P0122, P0123, P0131, P0132, P0133, P0134, P0151, P0152, P0153, P0154, P0300, P1133, P1134, P1153 and P1154 not set. |
| • | TP sensor between 5.4 and 25 degrees. |
| • | Coolant temperature 75°C (167°F) or greater. |
| • | Closed loop fuel control enabled. |
| • | Oxygen sensors ready. |
| • | Engine speed 800 RPM or greater. |
| • | MAP sensor greater than 32 kPa. |
| • | Above conditions met for 5 seconds. |
Failure Condition
Oxygen sensor has been lean (49 mV (0.049 V) or less) for 100 out of 120 seconds.
Action Taken When the DTC Sets
| • | The PCM will illuminate the malfunction indicator lamp (MIL) when the diagnostic runs and fails. |
| • | The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records. |
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 (current) 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 emission related 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.
Check snapshot data for front and rear long term fuel trim values. If both banks were lean, check for a condition that would cause lean engine operation
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
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If DTC P0146 is also set, diagnose it first because an oxygen sensor not ready can cause other emission related problems.
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If the oxygen sensor is operating correctly, voltage will fluctuate above 0.049 volt. A lean sensor/condition will cause the voltage to remain below 0.049 volt.
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 | |
Using a scan tool check for other DTC's. Is DTC P0146 also set? | -- | Go to DTC P0146 HO2S Circuit Insufficient Activity Bank 1 Sensor 3 | ||
Does voltage remain below the value specified for 30 seconds or more? | 85°C (185°F) 0.05 volts | Fault not present. | ||
4 |
Does the voltage remain below the value specified for 30 seconds or more? | 0.05 volts | ||
5 |
Is resistance greater than the value specified? | 10K ohms | ||
6 | Measure the resistance between post-converter oxygen sensor connector terminals A and B (harness side). Is the resistance the same or less than the value specified? | 5 ohms | ||
7 | Repair the short to ground on the Post HO2S High circuit. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- |
8 | Repair the Post HO2S High circuit and the Post HO2S Low circuit shorted together. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- |
9 | Replace the Post-Converter Heated Oxygen sensor. Refer to Heated Oxygen Sensor (HO2S) Replacement (Pre- and Post-Converter) . Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- |
10 | Replace the PCM. Refer to PCM Replacement/Programming . Is the replacement complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- |
