Circuit Description
In order to control emissions, a 3-way catalytic (TWC) converter converts any 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 TWC converter, produces an output signal which indicates the storage capacity of the catalyst. This in turn indicates the catalysts ability to convert the 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) 1.
Conditions for Running the DTC
| • | DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0171, P0172, P0201-P0204, P0300, P0301-P0304, P0336, P0440, P0446, P0452, P0453, P0506, P0507, P0601, P0602, or P1441 are not set. |
| • | The engine is in the power enrichment mode. |
| • | The battery voltage is more than 10 volts. |
| • | The engine coolant temperature (ECT) is more than 70°C (158°F). |
| • | The fuel level is more than 10 percent. |
| • | The engine has been running more than 10 seconds. |
Conditions For Setting The DTC
The HO2S 2 remains at less than 400 mV for more than 5 seconds. The diagnostic then will run for 11 seconds after a 5 second delay.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Diagnostic Aids
| • | The exhaust system--Inspect the exhaust system for the following conditions: |
| - | Leaks |
| - | Corrosion between the TWC converter and the flange |
| - | Loose or missing hardware |
| - | Repair any conditions as necessary. |
| • | A faulty electrical connection or a damaged harness--Inspect the harness for a short to ground in the HO2S 2 high signal circuit. Ensure that the HO2S 2 pigtail is not contacting the exhaust. |
| Inspect for the following conditions: |
| - | Wiring contacting the exhaust system |
| - | Improper mating |
| - | Broken locks |
| - | Improperly formed harness connectors |
| - | Damaged terminals |
| - | Faulty terminal to wire connection |
| - | A damaged harness |
| • | An intermittent test--Observe the HO2S 2 on the scan tool while moving any of the related electrical connectors and the wiring harness with the ignition ON. If the malfunction is induced, the HO2S 2 display will change. This should help to isolate the location of the malfunction. |
An intermittent can result from the following conditions:
| • | A faulty electrical connection |
| • | Rubbed through wire insulation |
| • | Broken wire inside the insulation |
Obstruction of the air reference and degraded HO2S 2 performance can result from any attempt to repair the HO2S harness or connector.
The HO2S 2 must have a clean air reference in order for the HO2S 2 to function properly. This clean air reference is obtained by way of the HO2S 2 wires.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step determines if DTC P1137 is the result of a hard malfunction or an intermittent condition.
-
You may need to jump the HO2S 2 low signal circuit to ground in order to allow the PCM to display the supplied bias voltage. The PCM and the wiring are OK if the voltage is between 0.35-0.55 volt .
Step | Action | Values | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||
2 | Are any other DTCs codes set? | -- | Go to Step 3 | |||||
Does the HO2S 2 voltage read less than the specified value? | 22 mV | Go to Step 5 | Go to Step 4 | |||||
4 |
Does the HO2S 2 voltage measure less than the specified value? | 40 mV | Go to Step 5 | Go to Diagnostic Aids | ||||
Caution: Avoid contact with moving parts and hot surfaces while working around a running engine in order to prevent physical injury. Does the scan tool indicate that the HO2S 2 voltage is within the specified value? | 350 mV-550 mV | Go to Step 8 | Go to Step 6 | |||||
6 |
Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 7 | ||||
7 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 10 | -- | ||||
8 | Inspect for poor connections at the harness connector of the HO2S sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Heated Oxygen Sensor Wiring Repairs in Wiring Systems. | -- | Go to Step 10 | Go to Step 9 | ||||
9 |
Caution: Avoid contact with moving parts and hot surfaces while working around a running engine in order to prevent physical injury. Did you complete the replacement? | -- | Go to Step 10 | -- | ||||
10 |
Does the DTC run and pass? | -- | Go to Step 11 | Go to Step 2 | ||||
11 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||
