| Table 1: | HO2S Voltages |
Circuit Description
The wide band heated oxygen sensor (HO2S) measures the amount of oxygen in the exhaust system and provides more information than the switching style HO2S. The wide band sensor consists of an oxygen sensing cell, an oxygen pumping cell, and a heater. The exhaust gas sample passes through a diffusion gap between the sensing cell and the pumping cell. The engine control module (ECM) supplies a voltage to the HO2S and uses this voltage as a reference to the amount of oxygen in the exhaust system. An electronic circuit within the ECM controls the pump current through the oxygen pumping cell in order to maintain a constant voltage in the oxygen sensing cell. The ECM monitors the voltage variation in the sensing cell and attempts to keep the voltage constant by increasing or decreasing the amount of current flow, or oxygen ion flow, to the pumping cell. By measuring the amount of current required to maintain the voltage in the sensing cell, the ECM can determine the concentration of oxygen in the exhaust. The HO2S voltage is displayed as a lambda value. A lambda value of 1 is equal to a stoichiometric air fuel ratio of 14.7:1. Under normal operating conditions, the lambda value will remain around 1. When the fuel system is lean, the oxygen level will be high and the lambda signal will be high or more than 1. When the fuel system is rich, the oxygen level will be low, and the lambda signal will be low or less than 1. The ECM uses this information to maintain the correct air/fuel ratio. If the ECM detects that the HO2S signal voltage is low, this DTC sets.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0131 HO2S Circuit Low Voltage Sensor 1
Conditions for Running the DTC
| • | The engine is operating. |
| • | The ignition 1 voltage is between 10.7-18 volts. |
| • | DTC P0131 runs continuously once the above conditions are met for more than 2 seconds. |
Conditions for Setting the DTC
| • | The internal ECM HO2S voltage is less than a threshold. |
| • | The above condition exists for more than 4 seconds. |
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 4 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 following table illustrates the ECM connector locations:
ECM Connector Location | |
|---|---|
C2 | C1 |
Front of Vehicle | |
| • | Use the J 35616-A/BT-8637 Connector Test Adapter Kit for any test that requires probing the ECM harness connector or a component harness connector. |
| • | The front wide band sensor does not toggle or switch like a switching HO2S. The front HO2S signal will be relatively stable for an idling engine. |
| • | For an intermittent condition, refer to Intermittent Conditions . |
| • | The following table illustrates the typical voltages for the HO2S circuits: |
HO2S Circuit | Voltage | ||||
|---|---|---|---|---|---|
| |||||
Heater Control | 4.6-5.0 V | ||||
Heater Supply Voltage | B+ | ||||
Reference Voltage | 2.6-3.1 V | ||||
Low Reference | 2.2-2.7 V | ||||
Pump Current | Less than 0.5 V | ||||
Input Pump Current | Less than 0.5 V | ||||
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step determines if the condition exists. If there is a short to ground condition with the HO2S circuits, the ECM commands open loop for the applicable sensor.
-
This step tests for a bias voltage across the reference voltage circuit and the low reference circuit of the HO2S. The bias voltage that you are measuring, is the voltage difference between the reference voltage circuit and the low reference circuit. If the reference voltage circuit or the low reference circuit of the HO2S is shorted to ground, the bias voltage will be above 1.5 volts, which indicates there is a condition with the circuits.
-
This step tests for a short to ground on the input pumping current circuit and the pump current circuit of the HO2S. The input pumping current circuit and the pump current circuit are connected internally within the ECM. If one of the circuits are shorted to ground, the other circuit will be affected. If you were to probe both circuits with a test lamp, the circuit that illuminates the test lamp brighter, is the circuit that is shorted to ground.
Step | Action | Values | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views | ||||||||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |||||||
|
Important: Inspect the heated oxygen sensor (HO2S) for being secure before proceeding with this DTC. A sensor that is loose could cause this DTC to set.
Does the scan tool display Closed Loop? | -- | Go to Step 3 | Go to Step 4 | |||||||
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids | ||||||
Is the voltage within the specified range? | 350-550 mV | Go to Step 5 | Go to Step 7 | |||||||
Connect a test lamp between the input pump current circuit and battery positive voltage. Does the test lamp illuminate? | -- | Go to Step 6 | Go to Step 11 | |||||||
6 |
Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 13 | ||||||
7 | Measure the voltage between the reference voltage circuit of the HO2S and a good ground. Refer to Circuit Testing . Is the voltage more than the specified value? | 1 V | Go to Step 8 | Go to Step 9 | ||||||
8 | Measure the voltage between the low reference circuit of the HO2S and a good ground. Is the voltage more than the specified value? | 1 V | Go to Step 12 | Go to Step 10 | ||||||
9 | Test the reference voltage circuit of the HO2S for a short to ground. Refer to Circuit Testing . Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 13 | ||||||
10 | Test the low reference circuit of the HO2S for a short to ground or for an open. Refer to Circuit Testing . Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 13 | ||||||
11 | Test for the following conditions:
Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 12 | ||||||
12 | Test for shorted terminals and poor connections at the HO2S. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 14 | ||||||
13 | Test for shorted terminals and poor connections at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 15 | ||||||
14 | Replace the HO2S. Refer to Heated Oxygen Sensor 1 Replacement . Did you complete the replacement? | -- | Go to Step 16 | -- | ||||||
15 | Replace the ECM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 16 | -- | ||||||
16 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 17 | ||||||
17 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||
