Circuit Description
The heated oxygen sensor (HO2S) is used in order to determine the oxygen content of the engine's exhaust. The oxygen content of the exhaust indicates when the engine is operating lean or rich. When the engine is operating lean, the exhaust will have more oxygen content. Once at operating temperature, the HO2S will produce a voltage in relation to the oxygen content of the exhaust. The HO2S requires an operating temperature of 360°C (600°F) to produce voltage. The HO2S will produce more voltage when the exhaust is rich and less voltage when the exhaust is lean. The HO2S operating voltage range is between 100 mV to 1,000 mV.
The powertrain control module (PCM) supplies a bias voltage to the HO2S. This bias voltage is near 450 mV. The Alternative Fuels ECM monitors the bias voltage as well as the voltage produced by the HO2S.
During normal Closed Loop fuel control operation, the Alternative Fuels ECM will add fuel when the HO2S indicates a lean exhaust content. When the HO2S indicates a rich exhaust content, the Alternative Fuels ECM will subtract fuel. This oscillation above and below the bias voltage can be monitored with a scan tool.
The oxygen sensor contains a heater. The heater is necessary in order to quickly warm the sensor to operating temperature. The heater will also maintain operating sensor temperature during extended idle conditions. A functioning oxygen sensor heater will allow the sensor to produce voltage in a short amount of time. A sensor at operating temperature will cause the HO2S signal voltage to go above or below the bias voltage.
This DTC indicates a HO2S signal voltage that did not leave the cold sensor bias voltage range in an acceptable amount of time.
Conditions for Running the DTC
| • | The engine is operating on alternative fuel. |
| • | No Alternative Fuels ECM ECT DTCs are set. |
| • | The start-up engine coolant temperature is less than 33°C (91°F). |
| • | The engine has been operating for at least 5 seconds. |
| • | The average mass air flow is less than 35 grams per second. |
| • | The battery voltage is more than 8 volts. |
| • | All other Alternative Fuels ECM DTCs for this HO2S sensor have ran and passed. |
| • | This DTC has not tested this ignition cycle. |
| • | The Alternative Fuels ECM determines the HO2S was cold at ignition key ON. A cold HO2S is indicated when the average HO2S signal voltage is within the bias voltage range of 300 mV to 600 mV when the ignition is turned ON. |
Conditions for Setting the DTC
The Alternative Fuels ECM detects a HO2S signal voltage that did not leave the cold sensor bias voltage range of 300 mV to 600 mV in an acceptable amount of time. The time varies from 50 seconds to 110 seconds based upon mass air flow.
Action Taken When the DTC Sets
| • | A first failure of this DTC will NOT illuminate the MIL and will store as Last Test Failed but not as History. |
| • | The Alternative Fuels ECM will illuminate the MIL and store the DTC as History after 2 consecutive drive trips that the diagnostic runs and fails. |
| • | The Alternative Fuels ECM will record operating conditions at the time the DTC sets. This information will be stored as Freeze Frame data. |
Conditions for Clearing the MIL/DTC
| • | The Last Test Failed status will clear when the DTC runs and passes. |
| • | The Alternative Fuels ECM will turn OFF the MIL after 3 consecutive drive trips that the DTC runs and passes. |
| • | The History status will clear after 40 consecutive WARM-UP cycles with NO failures of ANY DTC. |
| • | All DTC Information can be cleared with a scan tool. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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As the heater warms the oxygen sensor to operating temperature, the HO2S will output a voltage in relation to the amount of oxygen in the exhaust. With the ignition ON and the engine OFF, the exhaust usually contains a high oxygen content. With the engine OFF, the HO2S voltage will usually decrease from the bias voltage due to the high oxygen content.
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This step tests for a proper HO2S heater ignition feed and ground supply.
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This step tests for proper Control Module and signal circuit operation.
Step | Action | Value(s) | Yes | No | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||||||||||
1 | Did you perform the Diagnostic System Check Alternative Fuels - Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check - Alternative Fuels (Engine Controls) | ||||||||||||
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Important: The HO2S must be cool in order to prevent misdiagnosis.
Does the HO2S voltage increase or decrease from the initial voltage by at least the specified value? | 150 mV | Go to Step 3 | Go to Step 5 | |||||||||||||
3 |
Does the Alternative Fuels ECM indicate the same HO2S voltage as the PCM, plus or minus the specified value? | 45 mV | Go to Step 4 | Go to Step 9 | ||||||||||||
4 | The condition that set this DTC is not present. This DTC may have been set by one of the following conditions:
Repair any of the above conditions as necessary. Did you find and correct the condition? | -- | Go to Step 17 | Go to Intermittent Conditions | ||||||||||||
Turn ON the ignition, with the engine OFF. Does the test lamp illuminate? | -- | Go to Step 6 | Go to Step 7 | |||||||||||||
Is the voltage less than the specified value? | 20 mV | Go to Step 14 | Go to Step 8 | |||||||||||||
7 | Probe the ignition feed circuit of the HO2S heater with a test lamp connected to a good ground. Does the test lamp illuminate? | -- | Go to Step 11 | Go to Step 12 | ||||||||||||
8 |
Does the DMM display a resistance less than the specified value for both circuits? | 5 ohms | Go to Step 10 | Go to Step 13 | ||||||||||||
9 |
Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual. Did you find and correct the condition? | Go to Step 17 | Go to Step 15 | |||||||||||||
10 | Inspect the terminal tension at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems in the C/K Pickup Service Manual. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 16 | ||||||||||||
11 | Repair the open HO2S heater ground circuit. Refer to Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual. Did you complete the repair? | -- | Go to Step 17 | -- | ||||||||||||
12 | Repair the open or short to ground on the ignition feed circuit of the HO2S heater. Refer to Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual. Did you complete the repair? | -- | Go to Step 17 | -- | ||||||||||||
13 | Repair the circuit that measured high resistance. Refer to Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual. Did you complete the repair? | -- | Go to Step 17 | -- | ||||||||||||
14 | Replace the HO2S sensor. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 1 or Heated Oxygen Sensor Replacement - Bank 2 Sensor 1 in Engine Controls in the C/K Pickup Service Manual. Did you complete the replacement? | -- | Go to Step 17 | -- | ||||||||||||
15 | Replace the Alternative Fuels ECM. Refer to Alternative Fuels Engine Control Module Replacement . Did you complete the replacement? | -- | Go to Step 17 | -- | ||||||||||||
16 |
Important: KL6 models require a switchover to gasoline with a scan tool in order to perform the Crankshaft Position Variation Learn Procedure. KL8 models do not require the Crankshaft Position Variation Learn Procedure.Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls in the C/K Pickup Service Manual. Did you complete the replacement? | -- | Go to Step 17 | -- | ||||||||||||
17 |
Does the voltage increase or decrease from the initial voltage by at least the specified value? | 150 mV | Go to Step 18 | Go to Step 2 | ||||||||||||
18 | With a scan tool, select Capture Info in order to observe the stored information. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||||||||
