Circuit Description
Heated oxygen sensors (HO2S) are used in order to minimize the amount of time required to enter Closed Loop fuel control operation and to allow accurate catalyst monitoring. The HO2S 1 heater is fed power directly from ignition 1. The HO2S 1 heater control circuit or heater ground is connected to the powertrain control module (PCM). The PCM controls HO2S heater operation by grounding the control circuit via an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. The driver for the HO2S 1 heater control circuit has the ability to measure the amount of current drawn by the controlled device.
Conditions for Running the DTC
The engine is running.
Conditions for Setting the DTC
| • | The PCM detects that the heater control circuit current is greater than the capacity of the PCM internal driver. |
| • | Above condition is present for longer than 20 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 3 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. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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Check the HO2S heater current with the engine at operating temperature, and allow time for the heater current to stabilize. The HO2S heater current is initially higher until the sensor reaches full operating temperature.
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Ensures that the ignition 1 voltage circuit to the HO2S is not open or shorted. The test lamp should be connected to a good chassis ground in case the HO2S low reference or HO2S heater low control circuit is malfunctioning.
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Checks the HO2S heater low control circuit. The engine must be running for the PCM to enable the heater.
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Checks for a short to voltage in the HO2S heater control circuit.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
Is the O2 Heater Current within the specified range? | 0.25-0.85 Amps | Go to Intermittent Conditions | Go to Step 3 | |
3 | Inspect the fuse for the HO2S 1 ignition 1 voltage circuit. Is the fuse open? | -- | Go to Step 11 | Go to Step 4 |
Important:: Use a known good ground. Do not use the HO2S 1 heater low control circuit or the HO2S 1 low reference circuit. Does the test lamp illuminate? | -- | Go to Step 5 | Go to Step 7 | |
Does the test lamp illuminate? | -- | Go to Step 9 | Go to Step 6 | |
Does the test lamp illuminate? | -- | Go to Step 8 | Go to Step 12 | |
7 | Repair the open in the ignition 1 voltage circuit to the HO2S 1. Refer to Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you complete the action? | -- | Go to Step 14 | -- |
8 | Repair the short to voltage in the HO2S 1 heater low control circuit. Refer to Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you complete the action? | -- | Go to Step 14 | -- |
9 |
Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 10 |
10 | Replace HO2S 1. Refer to Heated Oxygen Sensor 1 Replacement in Wiring Systems. Did you complete the replacement? | -- | Go to Step 14 | -- |
11 | Locate and repair the short to ground in the HO2S 1 ignition 1 voltage circuit and replace the fuse. Refer to Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you complete the action? | -- | Go to Step 14 | -- |
12 |
Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 13 |
13 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- |
14 |
Does the scan tool indicate that the current is within the specified range? | 0.25-0.85 Amps | Go to Step 15 | Go to Step 2 |
15 |
Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
