Circuit Description
Heated oxygen sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature. The powertrain control module (PCM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started the PCM operates in open loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperatures and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream. Low HO2S voltage indicates a lean exhaust stream.
If the PCM detects that the HO2S voltage remains within the bias voltage range, DTC P0140 will set.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0140 HO2S Circuit Insufficient Activity Sensor 2
Conditions for Running the DTC
| • | DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0128, P0201-P0204, P0300, P0315, P0336, P0442, P0446, P0452, P0453, P0455, P0496, P0506, P0507, P0601, P0602, P1621 are not set. |
| • | The ECT Sensor parameter is more than 70°C (158°F). |
| • | No intrusive Catalyst Monitor tests are active. |
| • | The Ignition 1 Signal parameter is more than 11 volts. |
| • | The Fuel Level Sensor parameter is more than 10 percent. |
| • | The Engine Run Time parameter is more than 30 seconds. |
| • | The Air Flow Calculated parameter is more than 5.5 g/s for 70 seconds. |
| • | The TP Sensor parameter is between 8-56 percent. |
| • | The MAP Sensor parameter is more than 20 kPa. |
| • | The Loop Status parameter is closed. |
| • | DTC P0140 runs continuously when the above conditions are met. |
Conditions For Setting The DTC
| • | The PCM detects that the HO2S 2 parameter is between 425-473 mV. |
| • | DTC P0140 sets within 125 seconds when the above condition is met. |
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. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
An HO2S heater fault may set this DTC.
-
If the voltage is varying above and below the specified value, the condition is not present.
Step | Action | Value(s) | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views | ||||||||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | ||||||
Is the HO2S 2 heater current parameter within the specified range? | 0.217-1.56 A | Go to Step 3 | Go to DTC P0141 | |||||||
Did the HO2S 2 change more than the specified value? | 200 mV | Go to Step 4 | Go to Step 5 | |||||||
4 |
Did the DTC fail this ignition? | -- | Go to Step 5 | Go to Intermittent Conditions | ||||||
5 |
Is the HO2S 2 voltage parameter more than the specified value? | 800 mV | Go to Step 6 | Go to Step 7 | ||||||
6 |
Important: The normal voltage on the high signal circuit is between 400-500 mV. Important: The sensor may be damaged if the circuit is shorted to a voltage source. Test the HO2S 2 high signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 18 | Go to Step 17 | ||||||
7 |
Is the HO2S 2 voltage parameter within the specified range? | 400-500 mV | Go to Step 9 | Go to Step 8 | ||||||
8 |
Did you find and correct the condition? | -- | Go to Step 18 | Go to Step 14 | ||||||
9 |
Is the HO2S 2 voltage parameter within the specified range? | 400-500 mV | Go to Step 11 | Go to Step 10 | ||||||
10 |
Did you find and correct the condition? | -- | Go to Step 18 | Go to Step 15 | ||||||
11 | Measure the voltage from the high signal circuit of the HO2S 2 harness connector on the engine harness side to a good ground with a DMM. Refer to Circuit Testing in Wiring Systems. Is the voltage more than the specified value? | 1.0 V | Go to Step 12 | Go to Step 13 | ||||||
12 |
Important: The normal voltage on the low signal circuit is between 20-100 mV. Test the HO2S 2 low signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 18 | Go to Step 17 | ||||||
13 | Test the HO2S 2 high signal circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 18 | Go to Step 15 | ||||||
14 | Test for an intermittent and for a poor connection at the HO2S 2. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 18 | Go to Step 16 | ||||||
15 | Test for an intermittent and for a poor connection at the powertrain control module (PCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 18 | Go to Step 17 | ||||||
16 | Replace the HO2S 2. Refer to Heated Oxygen Sensor Replacement . Did you complete the replacement? | -- | Go to Step 18 | -- | ||||||
17 | Replace the PCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 18 | -- | ||||||
18 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 19 | ||||||
19 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | System OK | ||||||
