Circuit Description
The PCM supplies a bias voltage of about 450mV between the HO2S signal and low circuits. When measured with a 10 megaohm digital voltmeter, this may display as low as 320mV. The oxygen sensor varies the voltage within a range of about 1000mV when the exhaust is rich, down through about 10mV 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 HO2S 1 voltage remains at or near the 450mV 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 misfire, fuel injector circuit, TP sensor, EVAP, IAT sensor, MAP sensor, Fuel trim, EGR, ECT sensor, MAF sensor or CKP sensor DTC(s) present. |
| • | Engine run time longer than 30 seconds. |
| • | HO2S 1 signal voltage remains between 400mV and 500mV for longer than 10 seconds. |
| • | ECT greater than 65°C (149°F). |
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, engine off, 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 lights 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. |
Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.
Test Description
The numbers below refer to the step numbers on the Diagnostic Table:
-
This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming .
Step
| Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Powertrain On Board Diagnostic (OBD) System Check performed? | -- | ||
2 |
Does scan tool indicate 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 HO2S 1 voltage below the specified value? | 150 mV | ||
5 |
Does HO2S 1 signal voltage measure above the specified value? | 450 mV | ||
6 |
Was an HO2S 1 low circuit problem found and corrected? | -- | ||
7 |
Was a HO2S 1 signal circuit problem found and corrected? | -- | ||
8 | Check for a poor HO2S 1 signal or low circuit terminal connection at the HO2S 1 harness connector and replace terminal(s) if necessary. Refer to Repair Procedures in Electrical Diagnosis. Did any terminals require replacement? | -- | ||
9 | Check for poor HO2S 1 low circuit terminal connection at the PCM and replace terminal if necessary. Refer to Repair Procedures in Electrical Diagnosis. Did the terminal require replacement? | -- | ||
10 | Check for poor HO2S 1 signal circuit terminal connection at the PCM and replace terminal if necessary. Refer to Repair Procedures in Electrical Diagnosis. Did the terminal require replacement? | -- | ||
11 | Replace 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? | -- | Repair complete |
