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 around 450 mV.
This DTC sets when the HO2S signal voltage is above the normal operating range of the sensor.
• | The engine is operating on alternative fuel. |
• | The engine speed is more than 400 RPM. |
• | The engine coolant temperature (ECT) is above 70°C (160°F). |
• | The Alternative Fuels ECM determines the HO2S has been at operating temperature for at least 30 seconds. Operating temperature is indicated when engine coolant temperature is more than 40°C (104°F) AND desired gas flow is greater than 0.3 grams per second for 30 seconds. |
• | The Alternative Fuels ECM is operating in Closed Loop fuel control. |
The Alternative Fuels ECM monitors an HO2S signal voltage of more than 1,000 mV for 3 seconds continuously.
The Alternative Fuels ECM will Control fuel trim based upon the Bank 2 Sensor 1 signal. If a Bank 2 Sensor 1 DTC sets the Alternative Fuels ECM will operate in Open Loop fuel control.
• | 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. |
• | 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. |
The numbers below refer to the step numbers on the diagnostic table.
An HO2S contaminated by silicon will have a white, powdery deposit on the portion of the HO2S that is exposed to the exhaust stream. The usual cause of silica contamination is the use of unapproved silicon RTV engine gasket material or the use of silicon based sprays or fluids within the engine. If the cause of this contamination is not corrected, the replacement HO2S will also be contaminated.
An HO2S contaminated by silicon will have a white, powdery deposit on the portion of the HO2S that is exposed to the exhaust stream. The usual cause of silica contamination is the use of unapproved silicon RTV engine gasket material or the use of silicon based sprays or fluids within the engine. If the cause of this contamination is not corrected, the replacement HO2S will also be contaminated.
Step | Action | Value(s) | Yes | No | ||||||||||||||||||||
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Schematic Reference: Engine Controls Schematics | ||||||||||||||||||||||||
1 | Did you perform the Alternative Fuels Engine Controls Diagnostic System Check? | -- | Go to Step 2 | Go to Diagnostic System Check - Alternative Fuels (Engine Controls) | ||||||||||||||||||||
2 |
Is the voltage fixed at more than the specified value? | 800 mV | Go to Step 5 | Go to Step 3 | ||||||||||||||||||||
The condition that set this DTC is not present. This DTC may have been set by one of the following conditions:
Was a condition found and repaired? | -- | Go to Step 15 | Go to Step 4 | |||||||||||||||||||||
4 | The fault is not present. Refer to Diagnostic Aids. Are any DTCs stored that have not been diagnosed? | -- | Go to Intermittent Conditions | |||||||||||||||||||||
5 |
Is the voltage fixed at more than the specified value? | 800 mV | Go to Step 6 | Go to Step 12 | ||||||||||||||||||||
6 |
Is the voltage fixed at more than the specified value? | 800 mV | Go to Step 7 | Go to Step 11 | ||||||||||||||||||||
7 |
Is the voltage within the specified range? | 351-551 mV | Go to Step 8 | Go to Step 9 | ||||||||||||||||||||
Was a condition found and repaired? | -- | Go to Step 15 | Go to Step 13 | |||||||||||||||||||||
9 |
Is the voltage more than the specified value? | 20 mV | Go to Step 10 | Go to Step 14 | ||||||||||||||||||||
10 | Repair the HO2S signal High circuit short to voltage. Is the action complete? | -- | Go to Step 15 | -- | ||||||||||||||||||||
11 | The HO2S may be detecting a rich exhaust condition only during CNG operation. Perform the Fuel System Diagnosis and return to this step. Was a rich AF fuel system condition found and repaired? | -- | Go to Step 15 | Go to Step 12 | ||||||||||||||||||||
12 | Replace the Alternative Fuels ECM. Refer to Alternative Fuels Engine Control Module Replacement . Did you complete the replacement? | -- | Go to Step 15 | -- | ||||||||||||||||||||
13 | Replace the HO2S. 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 repair? | -- | Go to Step 15 | -- | ||||||||||||||||||||
14 |
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 15 | -- | ||||||||||||||||||||
15 |
Does the scan tool indicate the diagnostic passed? | -- | System OK | Go to Step 2 |