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. |
| • | HO2S 2 remains between 412-473 mV for 10 out of 12.5 minutes. |
| • | Engine has been running longer than 180 seconds. |
| • | The throttle position (TP) is between 0-50 percent. |
| • | Engine coolant temperature is greater than 70°C (158°F), |
| • | The vehicle is in Closed Loop. |
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 a poor connection rubbed through wire insulation, or a wire broken inside the insulation. Inspect for the following:
| • | Poor connection or damaged harness--Inspect the PCM harness for open in CKT 1668, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness. |
| • | Intermittent test--Observe the HO2S 2 on 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 P0140 is the result of a hard failure or an intermittent condition.
-
Disconnection the HO2S 2 and jumpering CKTs 1668 and 1669 to ground will determine if the PCM or wiring or HO2S 2 is at fault.
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Determines which circuit the fault is in. If CKT 1668 is OK, then the PCM connection or the PCM is faulty.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Was the On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | |
Does the scan tool display HO2S 2 voltage steady around the specified value? | 80°C (176°F) 1,200 RPM 450 mV | Go to Step 4 | Go to Step 3 | |
3 |
Does the scan tool display HO2S 2 voltage steady around the specified value? | 0.45 V (450 mV) | Go to Step 4 | Go to Diagnostic Aids |
Does the scan tool display HO2S 2 voltage below the specified voltage with the engine running? | 0.35 V (350 mV) | Go to Step 5 | Go to Step 6 | |
5 |
Was a problem found? | -- | Go to Step 7 | |
Does the test light illuminate? | -- | Go to Step 8 | Go to Step 9 | |
7 | Replace the HO2S 2. Is the action complete? | -- | -- | |
8 | Check for an open HO2S s high circuit or poor connection and repair as necessary. Was a repair necessary? | -- | Go to Step 10 | |
9 | Repair the open HO2S 2 low circuit. Is the action complete? | -- | -- | |
10 | Replace the PCM. Is the action complete? | -- | -- | |
