Circuit Description
The engine control module (ECM) supplies a voltage of about 0.45 volts between terminals A12 and A27. If measured with a 10 megohm digital voltmeter, this may read as low as 0.32 volts. The oxygen sensor (O2S) varies the voltage within a range of about 1 volt if the exhaust is rich, down through about 0.1 volts if the exhaust is lean.
The sensor is like an open circuit and produces no voltage when it is below 315°C (600°F). An open sensor circuit or cold sensor causes open loop operation.
If the O2S pigtail wiring, connector, or terminal is damaged, the entire O2S assembly must be replaced. Do not attempt to repair the wiring, connector, or terminals. In order for the sensor to function properly, it must have a clean air reference provided to it. This clean air reference is obtained by way of the O2S wires. Any attempt to repair the wires, connector, or terminals could result in the obstruction of the air reference and degrade the O2S performance.
Conditions for Setting the DTC
| • | The O2S voltage is between 300-600 mV. |
| • | The engine coolant temperature (ECT) is greater than 60°C (140°F). |
| • | System voltage is greater than 10 volts. |
| • | Engine run time is greater than 60 seconds. |
| • | Airflow is greater than 9 g/sec. |
| • | DTCs P0107, P0108, P0117, P0118, P0122, P0123, P0201, P0202, P0203, P0204, P0336, P0337, P0351, P0352, and P0443 are not set. |
| • | Three second delay after exiting decel fuel cut-off (DFCO) mode |
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate. |
| • | The ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers. |
| • | A history DTC is stored. |
| • | The vehicle will operate in open loop. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after 4 consecutive ignition cycles in which the diagnostic runs without a fault. |
| • | A history DTC will clear after 40 consecutive warm-up cycles without a fault. |
| • | The DTCs can be cleared by using the scan tool. |
| • | Disconnect the ECM battery feed for more than 10 seconds. |
Diagnostic Aids
Normal scan tool voltage varies from 150-850 mV while in closed loop. If DTC P0134 is intermittent, refer to Intermittent Conditions .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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The On-Board Diagnostic System Check prompts the technician to complete some basic checks and store the Freeze Frame and Failure Records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.
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During engine warm-up, the O2S should warm up, and its voltage output should vary between 150-850 mV. When the O2S voltage varies, the engine will go into closed loop. This determines if the O2S is operating properly.
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This will determine if the sensor is malfunctioning or if the wiring or the ECM is the cause of the DTC P0134.
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Use only a high impedance digital voltmeter (DVM) for this test. The test measures the continuity of the O2S signal and the ground circuits. If the ground circuit is open, the ECM voltage on the circuit will be over 0.6 volts (600 mV).
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The replacement ECM must be reprogrammed. Refer to the latest Techline procedure for ECM reprogramming.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Perform an On-Board Diagnostic System Check. Was the check performed? | -- | Go to Step 2 | ||
Does the scan tool display CLOSED LOOP? | -- | Go to Step 3 | Go to Step 4 | |
3 |
Does the scan tool display CLOSED LOOP? | -- | Go to Step 12 | Go to Step 4 |
Does the scan tool display the O2S voltage within the specified value? | 400-500 mV | Go to Step 5 | Go to Step 8 | |
5 | Inspect the O2S harness connector for malfunction or a poor connection and repair as needed. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 6 |
Is the voltage greater than the specified value? | 600 mV | Go to Step 7 | Go to Step 11 | |
7 |
Is the voltage less than the specified value? | 300 mV | Go to Step 9 | Go to Step 11 |
8 | Inspect the O2S low circuit for an open or short to ground between terminal 2 of the O2S and terminal A27 of the engine control module (ECM) and repair as needed. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 10 |
9 | Inspect the O2S signal circuit for an open or short to ground between terminal 2 of the O2S and terminal A12 of the ECM and repair as needed. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 10 |
Did you complete the replacement? | -- | Go to Step 12 | -- | |
11 | Replace the O2S. Refer to Heated Oxygen Sensor 1 Replacement and Heated Oxygen Sensor 2 Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- |
12 |
Does the scan tool indicate that this diagnostic has run and passed? | -- | Go to Step 13 | Go to Step 2 |
13 | Are any DTCs displayed that have not been diagnosed? | -- | Go to applicable DTC table | System OK |
