Circuit Description
The PCM supplies a bias voltage of about 450 mV between the HO2S signal and low circuits. When measured with a 10 megohm digital voltmeter, this may display as low as 320 mV. The oxygen sensor varies the voltage within a range of about 1000 mV when the exhaust is rich, down through about 10 mV when exhaust is lean. The PCM constantly monitors the HO2S signal during closed loop operation and compensates for a rich or lean condition by decreasing or increasing injector pulse width as necessary. If the Bank 1 HO2S 1 voltage remains at or near the 450 mV bias for an extended period of time, DTC P0134 will be set, indicating an open sensor signal or sensor low circuit.
Conditions for Setting the DTC
| • | No active transmission, TP sensor, EVAP system, EGR, misfire, IAT sensor, MAP sensor, fuel trim, fuel injector circuit, EVAP solenoid ODM, ECT sensor, or MAF sensor DTC(s) present. |
| • | Engine run time longer than 200 seconds. |
| • | Bank 1 HO2S 1 signal voltage remains between 400 mV and 500 mV for up to 30 seconds. |
Action Taken When the DTC Sets
| • | The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed. |
| • | The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic has been run and passed. |
| • | The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using the scan tool. |
Diagnostic Aids
Check for the following conditions:
| • | Poor connection or damaged harness -- Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness. |
| • | Faulty HO2S heater or heater circuit -- With the ignition ON the HO2S voltage displayed on a scan tool should gradually drop to below 250 mV or rise to above 600 mV. If not, disconnect the HO2S and connect a test light between the HO2S ignition feed and heater ground circuits. If the test light does not light, repair the open ignition feed or sensor ground circuit as necessary. Refer to Repair Procedures in Electrical Diagnosis . If the test light illuminates and the HO2S signal and low circuits are OK, replace the HO2S. |
| • | Intermittent test -- With the ignition ON, monitor the HO2S signal voltage while moving the wiring harness and related connectors. If the fault is induced, the HO2S signal voltage will change. This may help isolate the location of the malfunction. |
Review the Fail Records vehicle mileage since the diagnostic test last failed. This may help determine how often the condition that caused the DTC to be set occurs.
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table:
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||
2 |
Does scan tool indicate Bank 1 HO2S 1 voltage varying outside the specified values? | 400-500 mV | ||
3 |
Does scan tool indicate DTC failed this ignition? | -- | Go to Diagnostic Aids | |
4 |
Is Bank 1 HO2S 1 voltage below the specified value? | 150 mV | ||
5 |
Does Bank 1 HO2S 1 signal voltage measure near the specified value? | 450 mV | ||
6 |
Was a Bank 1 HO2S 1 low circuit problem found and corrected? | -- | ||
7 |
Was a Bank 1 HO2S 1 signal circuit problem found and corrected? | -- | ||
8 | Check for a poor Bank 1 HO2S 1 signal or low circuit terminal connection at the Bank 1 HO2S 1 harness connector and replace terminal(s) if necessary. Refer toHeated Oxygen Sensor (HO2S) Repair in Electrical Diagnosis. Did any terminals require replacement? | -- | ||
9 | Check for poor Bank 1 HO2S 1 low circuit terminal connection at the PCM and replace terminal if necessary. Refer to Wiring Repair in Electrical Diagnosis. Did the terminal require replacement? | -- | ||
10 | Check for poor Bank 1 HO2S 1 signal circuit terminal connection at the PCM and replace terminal if necessary. Refer to Wiring Repair in Electrical Diagnosis. Did the terminal require replacement? | -- | ||
11 | Replace Bank 1 HO2S 1. Refer to Heated Oxygen Sensor Replacement . Is the action completed? | -- | -- | |
Replace the PCM. Important: Replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | ||
13 |
Does scan tool indicate DTC failed this ignition? | -- | System OK | |
