Circuit Description
In order to control emissions, a catalytic converter is used to convert harmful exhaust emissions into harmless water vapor and carbon dioxide.
The powertrain control module (PCM) has the capability to monitor this process by using a rear heated oxygen sensor (HO2S) 2. The HO2S 2, located in the exhaust stream past the catalytic converter, produces an output signal which indicates the storage capacity of the catalyst. This in turn indicates the catalyst's ability to convert exhaust emissions effectively. If the catalyst is functioning properly, the HO2S 2 signal will be far less active than the signal produced by the front oxygen sensor (O2S).
If the O2S pigtail wiring, connector, or terminal are damaged the entire O2S assembly must be replaced. DO NOT attempt to repair the wiring, connector, or terminals. In order for the sensor to function properly, it must have a clean air reference provided to it. This clean air reference is obtained by way of the O2S wires. Any attempt to repair the wires, connectors, or terminals could result in the obstruction of the air reference and degrade oxygen sensor performance. Refer to Section 8A-5, Heated Oxygen Sensor (HO2S) Repair.
Conditions for Setting
| • | DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0200, P0300, P0301-P0304, P0441, P0562, P563, P1171, P1441 are not present. |
| • | The throttle position (TP) is between 5-50.2 percent. |
| • | Air/Fuel ratio is between 14.5-14.7 percent. |
| • | Engine coolant temperature is greater than 70°C (158°F), |
| • | The vehicle is in Closed Loop. |
| • | The above conditions are met for 50 seconds. |
| • | The HO2S 2 remains below 217 mV for 10 out of 12.5 minutes. |
| • | The engine has been running for more than 180 seconds. |
Action Taken
Malfunction indicator lamp (MIL) illuminates after two consecutive driving cycles with the fault active.
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after passing three consecutive diagnostic tests. |
| • | A history DTC will clear after 40 consecutive ignition cycles have occurred without a fault. |
| • | History and current DTCs can be cleared by using a scan tool. |
Diagnostic Aids
An intermittent may be caused by rubbed through wire insulation or wire contacting the exhaust. Inspect for the following:
| • | Exhaust System--Inspect the exhaust system for leaks. Check exhaust between the three way catalytic converter and flange for leaks, corrosion, or for loose or missing hardware and repair as necessary. |
| • | Poor connection or damaged harness--Inspect harness for a short to ground in CKT 1668, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness. Ensure that the HO2S 2 pigtail is not contacting the exhaust. |
| • | Intermittent test--Observe the HO2S 2 on the scan tool while moving related connectors and wiring harness with the key ON. If the failure is induced, the HO2S 2 display will change. This may help isolate the location of the malfunction. |
Test Description
The number below refers to the step number on the diagnostic table.
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This step determines if DTC P0137 is the result of a hard failure or an intermittent condition.
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Jumping CKT 1669 to ground is necessary to allow the PCM to display the supplied bias voltage. If the voltage is between 0.35-0.55 volt, then the wiring and PCM are OK.
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If CKT 1668 is shorted to ground, the HO2S 2 signal may vary between 300-400 mV.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Was the On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | |
Is the HO2S 2 voltage less than the specified value? | 75-95°C (167-203°F) 1,200 RPM 0.217 V (217 mV) | Go to Step 4 | Go to Step 3 | |
3 |
Is the HO2S 2 voltage less than the specified value? | 0.217 V (217 mV) | Go to Step 4 | Go to Diagnostic Aids |
Does the scan tool indicate HO2S 2 voltage within the specified range? | 0.35-0.55 V (350-550 mV) | Go to Diagnostic Aids | Go to Step 5 | |
Is the HO2S 2 high circuit shorted? | -- | Go to Step 6 | Go to Step 7 | |
6 | Repair short in the HO2S 2 high circuit. Is the action complete? | -- | -- | |
7 | Replace the PCM. Is the action complete? | -- | -- | |
