Circuit Description
Heated oxygen sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started, the powertrain control module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The PCM circuitry that monitors the HO2S generates a reference, or bias, voltage of 450 mV when the sensor is cold, high resistance. Once the HO2S warms up, the HO2S generates a voltage within a range of 0-1000 mV, depending on the exhaust gas oxygen content. High HO2S voltage output indicates a rich fuel mixture. Low HO2S voltage output indicates a lean mixture. Once fueling goes Closed Loop, the HO2S voltage will fluctuate above and below the bias voltage. A heating element inside the HO2S reduces the time required for the sensor to reach operating temperature, and provide an accurate voltage signal.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0200, P0300, P0351-P0358, P0400, P0401, P0404, P0405, P0410, P0440, P0442, P0443, P0446, P0449, P0452, P0453, P1120, P1125, P1220, P1221, P1258, P1404, P1441, P1514, P1515, P1516, P1517, or P1518 are not set. |
| • | The secondary air injection (AIR) and the exhaust gas recirculation (EGR) diagnostics are not active. |
| • | The ignition voltage is between 11-18 volts. |
| • | The system is in a Closed Loop. |
| • | The engine coolant temperature (ECT) is more than 60°C (140°F). |
| • | The engine has been running for more than 160 seconds. |
| • | The mass air flow (MAF) is between 29-55 g/s. |
| • | The engine speed is between 1,000-3,000 RPM. |
| • | The evaporative emission (EVAP) canister purge is more than 1 percent. |
| • | The accelerator pedal position (APP) indicated angle is more than 5 percent. |
Conditions for Setting the DTC
The number of lean-to-rich and rich-to-lean transitions within a 100 second sample period were less than 10.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
HO2S contamination is indicated if multiple response, switching, or time ratio HO2S DTCs are set.
-
The use of leaded fuel may be indicated by the removal or tampering of the fuel filler restrictor.
-
Even small exhaust leaks can cause slow response from the HO2S.
-
An HO2S contaminated by silicon will have a white, powdery deposit on the portion of the HO2S that is exposed to the exhaust stream. The usual cause of silica contamination is the use of unapproved silicon RTV engine gasket material or the use of silicon based sprays or fluids within the engine. If the cause of this contamination is not corrected, the replacement HO2S will also get contaminated.
-
If the voltage observed in step 8 is less than the range specified, a short between the HO2S high signal and low reference circuits or a short between the HO2S high signal circuit and ground is indicated. With the HO2S and the PCM disconnected, the resistance between the HO2S high signal and low reference circuits and the resistance between the HO2S high signal circuit and ground should measure infinite.
If the voltage observed in Step 8 is more than the range specified a short between the HO2S high signal circuit and an ignition voltage source is indicated.
-
If the voltage observed in Step 9 is not below the voltage specified, a high resistance, or open, in the HO2S high signal and low reference circuit is indicated.
Good circuit continuity measures less than 5 ohms with the PCM and sensor disconnected. Measure between the PCM connector and the HO2S connector. Ensure that the PCM terminal contact is good.
Step | Action | Values | Yes | No | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||||
Does the scan tool indicate the HO2S voltage varying above and below the specified values? | 351-551 mV | Go to Step 3 | Go to Step 4 | |||||||||||
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Intermittent Conditions | ||||||||||
Does the HO2S voltage measure below the specified range? | 20 mV | Go to Step 5 | Go to Step 8 | |||||||||||
5 |
Does the scan tool indicate that the HO2S voltage is less than the specified value? | 20 mV | Go to Step 6 | Go to Step 9 | ||||||||||
6 |
Does the test lamp illuminate? | -- | Go to Step 7 | Go to Step 10 | ||||||||||
Does the test lamp illuminate? | -- | Go to Step 12 | Go to Step 11 | |||||||||||
8 | Test the HO2S high signal circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 14 | ||||||||||
9 | Test the HO2S low signal circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | --- | Go to Step 17 | Go to Step 14 | ||||||||||
10 | Test the affected HO2S heater high control circuit for an open, high resistance, or short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 14 | ||||||||||
11 | Test the affected HO2S heater low control circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 14 | ||||||||||
|
Notice: Contamination of the oxygen sensor can result from the use of an inappropriate RTV sealant (not oxygen sensor safe) or excessive engine coolant or oil consumption. Remove the HO2S and visually inspect the portion of the sensor exposed to the exhaust stream in order to check for contamination. If contaminated, the portion of the sensor exposed to the exhaust stream will have a white powdery coating. Silicon contamination causes a high but false HO2S signal voltage (rich exhaust indication). The control module will then reduce the amount of fuel delivered to the engine, causing a severe driveability problem. Eliminate the source of contamination before replacing the oxygen sensor. Important: Before replacing the suspected HO2S, inspect and remove any source of contamination. Inspect for the following conditions:
Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 13 | |||||||||||
Inspect for poor connections at the harness connector of the affected HO2S. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 15 | |||||||||||
Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 16 | |||||||||||
15 | Replace the HO2S. Refer to Heated Oxygen Sensor Replacement - Bank 2 Sensor 1 or Heated Oxygen Sensor Replacement - Bank 1 Sensor 1 . Did you complete the replacement? | -- | Go to Step 17 | -- | ||||||||||
16 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 17 | -- | ||||||||||
17 |
Does the DTC run and pass? | -- | Go to Step 18 | Go to Step 2 | ||||||||||
18 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||||||
