Circuit Description
The PCM supplies a voltage of about 0.45 volt between the O2S signal and the ground circuit. The oxygen sensor (O2S 1) varies the voltage within the range of about 1.0 volt (1000 mV) if the exhaust is rich, down to about 0.1 volt (100 mV) if the exhaust is lean. The sensor is like an open circuit and produces no voltage when it is below 360°C (600°F). An open sensor circuit or a cold sensor causes open loop operation. DTC 44 determines if the O2S 1 sensor or the circuit is shorted low by checking for an extended lean condition.
If there is damage to the oxygen sensor pigtail wiring, the connector or the terminal, replace the entire oxygen sensor assembly. Do not attempt to repair the wiring, the connector or the terminals.
This is a type B DTC.
Conditions for Setting the DTC
| • | The vehicle is in CNG operation mode. |
| • | The engine is running at greater than 500 rpm. |
| • | The CNG fuel pressure sensor (FPS) voltage is greater than 1.95 volts (with the fuel level above 1/8 tank). |
| • | The ECT is greater than 70°C (160°F). |
| • | The oxygen sensor has been warm for at least 120 seconds. (The oxygen sensor is determined to be warm by the ECU if the ECT is greater than 40°C (104°F) and the calculated mass air flow is about 6 g/sec for at least 120 seconds.) |
| • | The ECU is in closed loop operation. |
| • | The O2S 1 voltage is less than 0.02 volt (20 mV). |
Action Taken When the DTC Sets
The MIL will be turned on after two consecutive ignition cycles in which the diagnostic runs with the fault active. The system will operate in open loop if any O2S DTC is set.
Conditions for Clearing the MIL/DTC
The ECU turns the MIL off after three consecutive ignition cycles without a fault condition present. A DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 40°C (72°F) from the start-up coolant temperature and the engine coolant temperature exceeds 70°C (160°F) during that same ignition cycle) or the code clearing procedure has been used.
Diagnostic Aids
Always diagnose ANY PCM codes that are present before beginning this diagnostic procedure.
Inspect for the following conditions:
| • | An oxygen sensor wire or a sensor pigtail may be mis-routed and contacting the exhaust manifold. |
| • | An intermittent ground in the wire between the connector and the sensor. |
| • | An open O2S 1 low circuit. |
| • | A poor ECU to the engine block ground. |
| • | A faulty mixture control valve (MCV). |
| • | A faulty high pressure regulator (HPR). |
| • | A faulty low pressure regulator (LPR). |
| • | An exhaust leak. If there is an exhaust leak, the engine may pull the outside air into the exhaust and past the sensor. |
| • | Vacuum or crankcase leaks can cause a lean condition and possibly a high idle. |
| • | If the above conditions do not exist, the problem may be a faulty oxygen sensor. |
Do not attempt to repair the wiring, the connector or the terminals. Never solder the O2S 1 wires.
Test Description
The number(s) below refer to the step number(s) on the diagnostic table.
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Removing the CNG system fuse will force the system to start on gasoline. The AF ECU is deactivated, but the Keep Alive Memory (KAM) contents is still retained. The gasoline operation will then allow the PCM to enable to O2S 1 sensor diagnostics. This may detect a similar fault, thereby isolating the fault to the base engine wiring harness or the O2S 1
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This step will verify the low voltage condition the ECU is detecting.
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This test determines if the sensor wiring or the ECU is the cause of DTC 44.
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If the O2S 1 low circuit is open, the ECU will detect the O2S 1 voltage as low even though the signal circuit has the correct input voltage.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the AF Powertrain OBD System Check performed? | -- | Go to Step 2 | Go to Alternative Fuels (AF) Powertrain On Board (OBD) System Check |
Is the action complete? | 1500 RPM | Go to Step 3 | -- | |
3 | Perform the AF Powertrain OBD System Check again. Is the action complete? | -- | Go to Step 4 | -- |
4 | Are there any powertrain DTCs displayed that have not been diagnosed? | -- | Go to the applicable powertrain DTC table | Go to Step 5 |
Does the DVOM indicate that the O2S 1 voltage remains below the specified value? | 20 mV | Go to Step 6 | Go to Step 7 | |
Does the DVOM indicate that the O2S 1 voltage is within the value specified? | 407-509 mV | Go to Step 8 | Go to Step 10 | |
7 |
Is there continuity? | -- | Go to Step 10 | Go to Step 11 |
8 |
Was a problem found? | -- | Go to Step 11 | Go to Step 9 |
9 | Replace the ECU. Refer to Engine Control Unit Replacement . Is the action complete? | -- | Go to Step 12 | -- |
Was a problem found? | -- | Go to Step 11 | Go to Diagnostic Aids | |
11 | Repair the circuit as necessary. Refer to Wiring Repairs in Engine Controls - 2.2L in the J Platform Service Manual. Is the action complete? | -- | Go to Step 12 | -- |
12 |
Did the MIL illuminate? | 1500 RPM | Go to Step 2 | Go to Step 13 |
13 | Are any ECU or PCM DTCs displayed that have not been diagnosed? | -- | Go to the applicable DTC table | System OK |
