Schematic Reference: Engine Controls Schematics
Circuit Description
The heated oxygen sensors (HO2S) increase the amount of time the sensor spends in closed loop fuel control operation or catalyst monitoring operation. The oxygen sensor heater greatly reduces the amount of time required for the fuel control HO2S (sensor 1) to become active. The oxygen sensor heater is required by the post-catalyst HO2S (sensor 2) in order to maintain the high operating temperatures. The heater helps provide accurate oxygen content readings of the engine exhaust by the HO2S.
Conditions for Setting the DTC
| • | Current of the HO2S heater is greater than 4 amps or less than 0.15 amps when the heater is ON. |
| • | Voltage of the HO2S heater is greater than 13.80 volts or lower than 10 volts when the heater is ON. |
| • | Voltage of the HO2S heater is 6 volts, with heater OFF. |
| • | One of the above conditions present for 3 seconds. |
Action Taken When the DTC Sets
| • | The engine control module (ECM) illuminates the malfunction indicator lamp (MIL) after two consecutive ignition cycles in which the diagnostic runs with the fault active. |
| • | The ECM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer. |
Conditions for Clearing the MIL/DTC
| • | The MIL turns OFF after three consecutively passing trips without a fault present. |
| • | A History DTC clears after 40 consecutive warm-up cycles without a fault. |
| • | Use the scan tool Clear DTC Information function or disconnect the ECM battery feed in order to clear the DTC. |
Diagnostic Aids
Check for a faulty electrical connection to the ECM.
An intermittent malfunction may be caused by a problem in the HO2S 2 sensor electrical circuit. Inspect the wiring harness and components for any of the following conditions:
| • | Backed out terminals. |
| • | Improper mating of terminals. |
| • | Broken electrical connector locks. |
| • | Improperly formed or damaged terminals. |
| • | Faulty terminal to wiring connections. |
| • | Physical damage to the wiring harness. |
| • | A broken wire inside the insulation. |
| • | Corrosion of electrical connections, splices, or terminals. |
If the DTC P0135 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.
Test Description
The numbers below refer to the step numbers in the Diagnostic Table.
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The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
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This step will determine if the fault is present.
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The HO2S 1 is powered by the IG Coil Meter fuse located in Fuse Block 1.
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Measures the resistance of the heater portion of the HO2S 1.
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This step checks for a short to ground in the HO2S 1 heater circuit. If no problem is found in the HO2S 1 heater circuit the fault could be a bad (shorted) HO2S 1.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | |||
Does the scan tool indicate a DTC P0135? | -- | Go to Diagnostic Aids | ||
Is the test light ON? | -- | |||
4 |
Is the voltage above the specified value? | 10 volts | ||
Is the HO2S 1 heater resistance within the specified value? | 11.7-14.3 ohms at 20°C (68°F) | |||
6 | Inspect the fuse in the fuse block. Is the fuse blown? | -- | ||
7 | Check the HO2S 1 heater control circuit for an open circuit or a short to ground. Repair as necessary. Refer to Wiring Repairs in Wiring Systems. Was a repair necessary? | -- | ||
Replace the faulty fuse and check the ignition feed circuit for a short to ground. Repair as necessary. Refer to Wiring Repairs in Wiring Systems. Was a repair necessary? | -- | |||
9 | Check for an open in the ignition feed circuit. Repair as necessary. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
10 | Check the connections at the HO2S 1 connector. Repair as necessary. Was a repair necessary? | -- | ||
11 | Replace the HO2S 1. Refer to Heated Oxygen Sensor Replacement. Is the action complete? | -- | -- | |
12 | Replace the ECM. Refer to Engine Control Module Replacement. Is the action complete? | -- | -- | |
13 |
Are any DTCs displayed on the scan tool? | -- | Go to the Applicable DTC Table | System OK |
