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 around 450 mV.
This DTC sets when the HO2S signal voltage is below the normal operating range of the sensor.
Conditions for Running the DTC
| • | 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. |
Conditions for Setting the DTC
The Alternative Fuels ECM monitors an HO2S signal voltage of less than 0.08 volts (78 mV) for 15 seconds continuously.
Action Taken When the DTC Sets
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. |
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. |
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) | ||||||||||||||||||||
2 |
Is the voltage fixed at less than the specified value? | 78 mV | Go to Step 3 | |||||||||||||||||||||
3 | The condition that set this DTC is not present. This DTC may have been set by one of the following conditions:
Did you find and correct the condition? | -- | Go to Step 16 | Go to Intermittent Conditions | ||||||||||||||||||||
4 |
Is the voltage fixed at less than the specified value? | 78 mV | Go to Step 5 | Go to Step 10 | ||||||||||||||||||||
5 |
Is the voltage fixed at less than the specified value? | 78 mV | Go to Step 6 | Go to Step 11 | ||||||||||||||||||||
6 |
Is the voltage within the specified range? | 351-551 mV | Go to Step 7 | Go to Step 8 | ||||||||||||||||||||
7 | The HO2S may be detecting a lean exhaust condition. Inspect for one of the following conditions:
Repair any of the above or similar engine conditions as necessary. Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 13 | ||||||||||||||||||||
8 |
Is the resistance infinite for both tests? | ∞ | Go to Step 14 | Go to Step 9 | ||||||||||||||||||||
9 | Repair the HO2S signal High circuit short to ground or short to the HO2S Low circuit. Refer to Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual. Did you complete the repair? | -- | Go to Step 15 | |||||||||||||||||||||
10 |
Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 12 | ||||||||||||||||||||
11 | The HO2S may be detecting a lean exhaust condition only during CNG operation. Perform the Fuel System Diagnosis and return to this step. Was a lean Alternative Fuels 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 replacement? | -- | 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 DTC run and pass? | -- | Go to Step 16 | Go to Step 2 | ||||||||||||||||||||
16 | 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 | |||||||||||||||||||||
