Circuit Description
Heated oxygen sensors (HO2S) are used 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 outside a calibrated range.
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. |
Diagnostic Aids
Notice: Use the connector test adapter kit J 35616-A for any test that
requires probing the following items:
• The PCM harness connectors • The electrical center fuse/relay cavities • The component terminals • The component harness connector
Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help to determine how often the condition occurs that caused the DTC to set . This may assist in diagnosing the condition.
If the problem is intermittent, refer to Intermittent Conditions .
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 the full operating temperature.
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This 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.
-
This checks the HO2S heater low control circuit. The engine must be running for the PCM to enable the heater.
-
This 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 current within the specified range? | 0.45-0.65 A | Go to Diagnostic Aids | 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 signal 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 9 | |
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 repair? | -- | 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 repair? | -- | Go to Step 14 | -- |
9 |
Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 10 |
10 | Replace the HO2S 1. Refer to Heated Oxygen Sensor 1 Replacement . 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 find and correct the condition? | -- | 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 DTC run and pass? | -- | Go to Step 15 | Go to Step 2 |
15 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
