Circuit Description
To control emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides of Nitrogen (NOx), a three-way catalytic converter is used. The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas, converting them into harmless water vapor and carbon dioxide. The catalyst also reduces NOx, converting it to nitrogen. The PCM has the ability to monitor this process using the Bank 1 HO2S 3 heated oxygen sensor. The Bank 1 HO2S 3 sensor produces an output signal which indicates the oxygen storage capacity of the catalyst; this in turn indicates the catalyst's ability to convert exhaust gases efficiently. If the Bank 1 HO2S 3 signal voltage remains at or near the 450mV bias for an extended period of time, DTC P0146 will be set.
Conditions for Running the DTC
| • | No Misfire, CKP, Fuel Injector, MAF, TP, EVAP, IAT, MAP, Fuel Trim, EGR or ECT DTCs are set. |
| • | Engine has been running for more than 4 minutes. |
Conditions for Setting the DTC
Bank 1 HO2S 3 signal voltage remains between 425 mV and 475 mV during normal closed loop operation.
Action Taken When the DTC Sets
| • | The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed. |
| • | The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic has been run and passed. |
| • | The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using the scan tool. |
Diagnostic Aids
Check for the following conditions:
| • | Corroded exhaust flange bolts - Using a J 39200 Digital Multimeter, ensure that continuity exists between the engine block and the heated oxygen sensor shell. If resistance is excessively high, replace corroded exhaust flange attaching hardware as necessary. |
| • | Poor connection at the PCM - Inspect harness connectors for the following conditions: |
| - | Backed out terminals. |
| - | Improper mating. |
| - | Broken locks. |
| - | Improperly formed or damaged terminals. |
| - | Poor terminal to wire connection. |
| • | Faulty HO2S heater or heater circuit - With the ignition ON the HO2S voltage displayed on a scan tool should gradually drop to below 300mV or rise to above 600mV. If not, disconnect the HO2S and connect a test light between the HO2S ignition feed and heater ground circuits. If the test light does not light, repair the open ignition feed or sensor ground circuit as necessary. Refer to Wiring Repairs If the test light lights and the HO2S signal and low circuits are OK, replace the HO2S. Refer to Heated Oxygen Sensor Replacement |
| • | Intermittent test - With the ignition ON, monitor the HO2S signal voltage while moving the wiring harness and related connectors. If the fault is induced, the HO2S signal voltage will change. This may help isolate the location of the malfunction. |
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table:
-
If the this DTC test passes while the Fail Records conditions are being duplicated, an intermittent condition is indicated. Review the Fail Records vehicle mileage since the diagnostic test last failed. This may help determine how often the condition that caused the DTC to be set occurs.
-
This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM isreplaced, the new PCM must be programmed.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||
2 |
Does scan tool indicate HO2S voltage varying outside the specified values? | 424-475 mV | ||
Does the scan tool indicate this DTC failed this ignition? | -- | Go to Diagnostic Aids | ||
4 |
Does the scan tool indicate HO2S voltage less than the specified value? | 150 mV | ||
5 |
Does the voltage measure near the specified value? | 4.5 V | ||
6 |
Did you find and correct the condition? | -- | ||
7 |
Did you find and correct the condition? | -- | ||
8 | Inspect for a poor signal circuit or low circuit connection at the HO2S. Refer to Intermittents and Poor Connections Diagnosis and Connector Repairs . Did you find and correct the condition? | -- | ||
9 | Inspect for a poor low circuit connection at the PCM. Refer to Intermittents and Poor Connections Diagnosis and Connector Repairs . Did you find and correct the condition? | -- | ||
10 | Inspect for poor signal circuit and low circuit connections at the PCM. Refer to Intermittents and Poor Connections Diagnosis and Connector Repairs . Did you find and correct the condition? | -- | ||
11 | Replace HO2S. Refer to Heated Oxygen Sensor Replacement . Did you complete the replacement? | -- | -- | |
12 |
Important: Replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Did you complete the replacement? | 100 ohms | -- | |
Test for poor signal circuit connection at the PCM and repair as necessary. Refer to Intermittents and Poor Connections Diagnosis and Connector Repairs . Did you find and correct the condition? | -- | -- | ||
14 | Locate and repair cause of high resistance (corroded exhaust flange bolts, separated exhaust flange). Did you complete the repair? | -- | -- | |
15 |
Does the DTC reset? | -- | System OK |
