Circuit Description
The heated oxygen sensor (HO2S) is a sensor designed to create a voltage relative to the oxygen content in the engine exhaust stream. The control module supplies the HO2S with signal high and low circuits. Ignition voltage and ground are supplied to the HO2S heater by independent circuits. The oxygen content of the exhaust indicates when the engine is operating lean or rich. When the HO2S detects that the engine is operating rich, the signal voltage is high, and decreases the signal voltage as the engine runs leaner. This oscillation above and below the bias voltage, sometimes referred to as activity or switching, can be monitored with the HO2S signal voltage.
The HO2S contains a heater that is necessary in order to quickly warm the sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. The HO2S needs to be at a high temperature in order to produce a voltage. When the HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. It also monitors the HO2S signal voltage for Closed Loop fuel control. During normal Closed Loop fuel control operation, the control module will add fuel, or enrich the mixture, when the HO2S detects a lean exhaust content. The control module will subtract fuel, or "lean-out" the mixture, when the HO2S detects a rich exhaust condition.
Certain vehicle models utilize an oxygen sensor behind the catalytic converter in order to monitor catalyst efficiency.
This diagnostic trouble code (DTC) determines if the HO2S is functioning properly. It checks for an adequate number of HO2S voltage transitions above and below the bias range of 300-600 mV. This DTC sets when the vehicle control module (VCM) fails to detect a minimum number of voltage transitions above and below the bias range during the test period. Possible causes of this DTC are:
| • | An open or a short to voltage on either the HO2S signal or HO2S low circuits |
| • | A malfunctioning HO2S |
| • | A problem in the HO2S heater or its circuit |
| • | A faulty HO2S ground |
This DTC determines if the HO2S heater circuit is functioning properly by monitoring the amount of time required for the HO2S to reach operating temperature. This DTC sets when the VCM fails to detect HO2S voltage transitions above and below the bias range within a specified amount of time. Possible cause of this DTC are listed below:
| • | An open circuit in either the HO2S ignition feed or the HO2S heater ground circuits |
| • | An HO2S heater element problem |
Conditions for Running the DTC
Important: This test is void for this cold start if the system voltage remains outside the specified range for more than 4 seconds.
| • | The system voltage is between 11.7-17 volts |
| • | The MAF is less than 27 g/s |
| • | The engine run time is greater than 2 seconds |
| • | The ECT is less than 33°C (91°F) |
| • | The IAT is less than 33°C (91°F) |
| • | The difference between the ECT and IAT is no more than 5°C (41°F) or less |
Conditions for Setting the DTC
The O2 sensor voltage remains between 300-600 mV range for a specified amount of time. The amount of time is based on start-up coolant temperature and average air flow and is limited to a maximum of 130 seconds.
Action Taken When the DTC Sets
The VCM turns the MIL ON after 2 consecutive test failures.
Conditions for Clearing the MIL or DTC
| • | The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed. |
| • | A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle. |
| • | Use a scan tool in order to clear the DTCs. |
Diagnostic Aids
Important: Never solder the HO2S wires. For proper wire and connection repairs, refer to Wiring Repairs .
| • | Check for a poor connection or a damaged harness. |
| • | Inspect the harness for the following conditions: |
| - | Backed out terminals |
| - | Improper mating |
| - | Broken locks |
| - | Improperly formed or damaged terminals |
| - | A poor terminal to wire connection |
| - | A damaged harness |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step checks for proper sensor activity. When in Closed Loop fuel control the HO2S voltage should rapidly swing above and below the bias voltage.
-
This step checks the VCM and the HIGH and LOW circuits between the VCM and the HO2S connector for proper operation.
-
This step checks for proper HO2S heater circuit operation up to the HO2S connector.
-
This step checks for proper circuit resistance between the HO2S LOW circuit and VCM ground.
-
This step checks for proper circuit resistance between the HO2S LOW circuit and VCM ground with a COLD sensor. A loose HO2S or poor tread to exhaust electrical contact will cause higher resistance when the HO2S is cold. Although 500 ohms is allowed, typical resistance should be less than 50 ohms.
Step | Action | Value(s) | Yes | No | ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 |
Important: Before clearing the DTCs, use the scan tool Capture Info function to save the Freeze Frame and the Failure Records for reference. The control module's data is deleted once the Clear DTC Information function is used. Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||||||||||||||||||||
Is the HO2S voltage within the specified range? | 351 mV-551 mV | |||||||||||||||||||||
3 | The condition that set this DTC is not present. This DTC may have been set by one of the following conditions:
Repair any of these conditions as necessary. Did you perform a repair? | -- | Go to Diagnostic Aids | |||||||||||||||||||
Is the voltage less than the specified value? | 20 mV | |||||||||||||||||||||
5 |
Is the resistance of both circuits less than the specified value? | 5 ohms | ||||||||||||||||||||
6 |
Did you perform a repair? | -- | ||||||||||||||||||||
Is the test lamp ON? | -- | |||||||||||||||||||||
Is the resistance less than the specified value? | 500 ohms | |||||||||||||||||||||
9 | Repair the circuit that measured high resistance. Refer to Wiring Repairs . Is the action complete? | -- | -- | |||||||||||||||||||
10 | Inspect the HO2S heater ignition or ground circuit for any of the following conditions:
Repair the circuit as necessary. Is the action complete? | -- | -- | |||||||||||||||||||
11 | Repair the high resistance between the HO2S LOW circuit and the VCM ground circuit. Refer to Wiring Repairs .Probable causes include the following:
Is the action complete? | -- | -- | |||||||||||||||||||
12 |
Did you perform a repair? | -- | ||||||||||||||||||||
Is the resistance less than the specified value? | 500 ohms | |||||||||||||||||||||
14 |
Is the resistance less than the specified value? | 500 ohms | ||||||||||||||||||||
15 | Replace the HO2S. Refer to Heated Oxygen Sensor Replacement . Is the action complete? | -- | -- | |||||||||||||||||||
16 |
Is the replacement complete? | -- | -- | |||||||||||||||||||
17 |
Does the scan tool indicate the diagnostic passed? | -- | ||||||||||||||||||||
18 | Does the scan tool display any additional undiagnosed DTCs? | -- | Go to the applicable DTC table | System OK |
