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P0132 and P0138 - Oxygen Sensor Circuit High Voltage


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Old 07-28-2006, 12:35 PM   #1
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We put together the following information about the P0132 and P0138 fault code. We have also included diagnostic procedures below to aid in analyzing the code.

OBD II Fault Code

OBD II P0132
OBD II P0138

Fault Code Definition

The Power Train Computer or PCM has determined that the Oxygen Sensor voltage remained above 900 millivolts for more than two minutes (varies with vehicle make and model) or that the Air Fuel Ratio Sensor remained in a rich-biased mode for too long (varies with vehicle make and model).

OBD II P0132 Oxygen Sensor Circuit High Voltage (Bank 1 Sensor 1)
OBD II P0138 Oxygen Sensor Circuit high Voltage (Bank 1 Sensor 2)

Symptoms
  • Check Engine Light will illuminate
  • Vehicle may idle or run rough
  • Decrease in fuel Eeconomy because PCM is in a "limp home" mode
  • Engine dies
  • In some unusual cases, there are no adverse conditions noticed by the driver

Common Problems that Trigger the P0132 and P0138 Code
  • Defective Oxygen Sensor/Air Fuel Ratio Sensor
  • Defective Oxygen Sensor/Air Fuel Ratio Sensor Heater circuit
  • High Fuel Pressure
  • Defective Engine Coolant Temperature Sensor
  • Defective sensor wiring and/or circuit problem
  • PCM software needs to be updated
  • Defective PCM

Polluting Gases Expelled
  • HCs (Hydrocarbons): Unburned droplets of raw fuel that smell, affect breathing, and contribute to smog
  • NOX (Oxides of Nitrogen): One of the two ingredients that, when exposed to sunlight, cause smog

Want to Learn More?

The purpose of codes P0132 and P0138 is to track the amount of time that the Oxygen Sensor or Air Fuel Ratio Sensor stays in a very rich signal/condition before moving to a lean signal/condition. If the signal stays stuck in a very rich mode and/or is set very high for two minutes or more—which is generally above 900 millivolts for an Oxygen Sensor—then the code P0132 or P0138 is triggered.

The switching time and voltage of an Air Fuel Ratio Sensor can also be observed using a scanner, though this data is only an approximation created by the Power Train Control Module for diagnostic purposes. In order to set, this Oxygen Sensor/Air Fuel Ratio Sensor code usually requires malfunctions on two different drive cycles by the vehicle; however, if the problem is severe enough, the code can set in less than fifteen minutes on an initial test drive, after the clearing of all codes. In other words, the code setting criteria varies from vehicle to vehicle.

P0132 and P0138 Diagnostic Theory for Shops and Technicians:
Oxygen Sensor


When the code P0132 or P0138 is set, record the freeze frame data in fine detail. Next, duplicate the code setting conditions on a test drive, paying particular attention to load, MPH, and RPM. The best tool to use on this test drive is a data streaming scan tool that has factory quality and dedicated live data. Be sure to verify the code conditions before you advance to the next set of tests.

If You Cannot Verify the Code Setting Malfunction

If you cannot verify the code setting malfunction, then do a careful visual inspection of the sensor and the connections. Verify that there are 12-volt heater signal(s) and good ground(s) to the sensor and that they follow the required times, per the manufacturer diagnostic documentation. Verify that the signal from the Oxygen Sensor to the PCM is being "seen" by back probing the Oxygen Sensor connector and, if needed, back probing the signal wire at the PCM. Inspect the sensor harness to ensure that it isn't chafed and/or grounding anywhere and be sure to perform a wiggle test. You will want to use a high impedance Digital Volt Ohm Meter (DVOM) for all of these electrical tests. If you still cannot find a problem, then try these steps next:
  • If you can receive authorization from the customer to keep the vehicle overnight, clear the code and test drive the vehicle by driving it home and then back to work in the morning, making sure that you are duplicating the code setting driving conditions on both trips. If the code still does not come back, you can give the customer the option of replacing the Oxygen Sensor as a diagnostic step since the sensor is the most likely problem and the code will presumably set again. If the customer declines, then return the vehicle with a clear description of the inspections and your findings plainly attached to the final copy of the repair order. Keep another copy for your own records in case you have to re-visit this inspection for any reason.
  • If this is an inspection for an emissions failure, most government programs suggest that you replace the sensor as a preventative measure so the vehicle won't remain in a highly polluting operational condition. After the Oxygen Sensor is replaced, the monitors will have to be re-set and this, too, will test most phases of the Oxygen Sensor system to ensure that the problem was solved. Be sure to verify that the Mode 6 test IDs and component IDs that pertain to fuel control are well within the parameter limits. If there is a problem with re-setting the monitors, continue the inspection until you find the root cause of the problem.

If You Can Verify the Code Setting Malfunction

If you can verify the code setting malfunction, then do a careful visual inspection of the sensor, the connections, and the exhaust system. Verify that there are 12-volt heater signal(s) and good ground(s) to the sensor and that they follow the required times, per the manufacturer diagnostic documentation. Verify that the signal from the Oxygen Sensor to the PCM is being "seen" by back probing the Oxygen Sensor connector and, if needed, back probing the signal wire at the PCM. Inspect the sensor harness to ensure that it isn't chafed and/or grounding anywhere and be sure to perform a wiggle test. You will want to use a high impedance Digital Volt Ohm Meter (DVOM) for all of these electrical tests.
  • The most comprehensive way to test and condemn an Oxygen Sensor Heater Circuit is to use a Dual Trace Labscope with the time division graticule set at 100-millisecond intervals and the voltage scale set at +/- 2 volts. Run the warmed-up vehicle with the signal wire back probed and watch to see if the signal sticks above 900 millivolts and for how long. Do this while the engine is idling and at 2000 RPM. A properly working Oxygen Sensor should switch from lean (less than 300 millivolts) to rich (above 750 millivolts) in less than 100 milliseconds and should do it consistently. The voltage should only stick in a very high mode during wide open throttle operation, when the system is in open loop.
  • Next, perform a range test and time test, still using the Labscope. Run the engine at 2000 RPM and quickly close the throttle and then snap it back open. The Oxygen Sensor Signal needs to go from around 100 millivolts (when the throttle closes) to above 900 millivolts (when the throttle opens) in less than 100 milliseconds. A new sensor will do this test within these ranges in less than 30–40 milliseconds. A good sensor should never stick in a really high mode.
  • If the sensor fails either of the above Labscope inspections, most emissions programs will allow you to condemn the sensor because the slow switching time leads to high NOx levels and above-normal CO levels and HCs. This is because the Cerium bed of the OBD II Catalytic Converter is not being supplied with the proper amount of Oxygen each time the signal "lags" between the peaks and valleys of its sine wave.

    Note: If the Oxygen Sensor signal ever goes to a negative voltage or above 1 volt, this alone is enough to condemn the sensor. These out-of-range readings are often caused by the Heater Circuit bleeding voltage or ground into the Oxygen Sensor signal circuit. They can also be caused by contamination or physical damage to the sensor.
  • If the above tests and inspections don't produce verifiable results, then physically remove the Oxygen Sensor. If the Sensor Probe has a white and chalky appearance, the sensor has been lagging between switching phases and needs to be replaced. It should have the light tannish coloration of a healthy spark plug.

P0132 and P0138 Diagnostic Theory:
Air Fuel Ratio Sensor


Most Air Fuel Ratio Sensors are basically two heated Oxygen Sensors that work in tandem in order to create a much faster responding Oxygen Sensor/Fuel Control System. These systems are also capable of "'broadband" operation, which means that the vehicle will remain in closed loop and maintain active long term and short term fuel control during wide open throttle conditions. A conventional Oxygen Sensor System cannot maintain fuel control when the throttle is above 50 percent and the vehicle is under heavy load, such as wide open throttle.

When the code P0132 or P0138 is set, record the freeze frame data in fine detail. Next, duplicate the code setting conditions on a test drive, paying particular attention to load, MPH, and RPM. The best tool to use on this test drive is a data streaming scan tool that has factory quality and dedicated live data. Be sure to verify the code conditions before you advance to the next set of tests.

If You Cannot Verify the Code Setting Malfunction

If you cannot verify the code setting malfunction, then do a careful visual inspection of the sensor and the connections. Verify that there are 12-volt heater signal(s) and good ground(s) to the sensor and that they follow the required times, per the manufacturer diagnostic documentation. Verify that the signal from the Oxygen Sensor to the PCM is being "seen" by back probing the Oxygen Sensor connector and, if needed, back probing the signal wire at the PCM. Inspect the sensor harness to ensure that it isn't chafed and/or grounding anywhere and be sure to perform a wiggle test. You will want to use a high impedance Digital Volt Ohm Meter (DVOM) for all of these electrical tests. If you still cannot find a problem, then try these steps next:
  • If you can receive authorization from the customer to keep the vehicle overnight, clear the code and test drive the vehicle by driving it home and then back to work in the morning, making sure that you are duplicating the code setting driving conditions on both trips. If the code still does not come back, you can give the customer the option of replacing the Oxygen Sensor as a diagnostic step since the sensor is the most likely problem and the code will presumably set again. If the customer declines, then return the vehicle with a clear description of the inspections and your findings plainly attached to the final copy of the repair order. Keep another copy for your own records in case you have to re-visit this inspection for any reason.
  • If this is an inspection for an emissions failure, most government programs suggest that you replace the sensor as a preventative measure so the vehicle won't remain in a highly polluting operational condition. After the Oxygen Sensor is replaced, the monitors will have to be re-set and this, too, will test most phases of the Oxygen Sensor system to ensure that the problem was solved. Be sure to verify that the Mode 6 test IDs and component IDs that pertain to fuel control are well within the parameter limits. If there is a problem with re-setting the monitors, continue the inspection until you find the root cause of the problem.

If You Can Verify the Code Setting Malfunction

If you can verify the code setting malfunction, then do a careful visual inspection of the sensor, the connections, and the exhaust system. Verify that there are 12-volt heater signal(s) and good ground(s) to the sensor and that they follow the required times, per the manufacturer diagnostic documentation. Verify that the signal from the Oxygen Sensor to the PCM is being "seen" by back probing the Oxygen Sensor connector and, if needed, back probing the signal wire at the PCM. Inspect the sensor harness to ensure that it isn't chafed and/or grounding anywhere and be sure to perform a wiggle test. You will want to use a high impedance Digital Volt Ohm Meter (DVOM) for all of these electrical tests.

There are numerous, complex tests for an Air Fuel Ratio Sensor, but these are the simplest and most time-efficient tests:
  • Air Fuel Ratio Senors may have several wires, but there are two key wires. Using a DVOM with the key on and the engine off, disconnect the sensor and probe the harness going to the PCM. Make sure one wire has 3.0 volts and another wire has 3.3 volts. The other wires are the 12-volt power(s) and ground(s) for the heater circuits. In some cases, you may have to start the engine and let it idle to find the proper voltages on all the wires.
  • Use jumper wires to connect the sensor to the harness. Connect your DVOM in series with the 3.3 volt wire. Turn your DVOM to the milliamp scale and start the engine, letting it idle. The 3.3 volt wire should cross-count between +/- 10 milliamps. Vary the RPM and as you add and decrease throttle, you should see the signal respond to subtle changes in mixture. If you don't consistently see the +/- 10 milliamp variation in this wire, then the Air Fuel Ratio Sensor is defective.
  • If all the above tests and inspections do not produce verifiable results, then physically remove the Air Fuel Ratio Sensor. If the Sensor Probe has a white and chalky appearance, the sensor has been lagging between switching phases and needs to be replaced. It should have the light tannish coloration of a healthy spark plug.

_____________________________________________
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check engine light, defective o2 sensor, dtc ii p0132, dtc ii p0138, high fuel pressure, o2 sensor, obd ii p0132, obd ii p0138, oxygen sensor circuit high voltage, oxygen sensor circuit high voltage bank 1 sensor 1, oxygen sensor circuit high voltage bank 1 sensor 2, rough idle


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