The heated oxygen sensor (Front)generates output voltages between 0V and 1V in response to the oxygen concentration in exhaust gas.When the output of the heated o2 sensor is .55V or more, the ECM judges that the air/fuel ratio is RICH.When it is 0.40V or less, the ECM judges that the air/fuel ratio is LEAN. If the oxygen sensor cannot output enough voltage to reach the minimum specification, the ECM interprets this as a malfunction in the oxygen sensor and sets a DTC.
Fail A: Sensor voltage is 0.55 V or less for 18 seconds or more.
Fai B: Sensor voltage is 0.40 V or more for 18 seconds or more.
Component operating range.
When normal, voltages output from the oxygen sensor produce a waveform alternating between 0 V and 1V.
P0133(BANK1) Front Oxygen sensor slow response.
P0153 (Bank2) -DO-
Typical malfunction thresholds
Detection criteria:Time taken by heated O2 sensor for increase in voltage from 0.4 to 0.55 V
and time taken to decrease from 0.55V to 0.4 V.
Threshold : 20 sec, or more X 3 times.
Bank 1 sensor 1 = before cat.
Bank 1 sensor 2 = after cat.
Code P0133 reads "Bank 1 Sensor 1 circuit slow response"; meaning the front oxygen sensor (located before catalytic converter) has slow response time to the changes in the air-fuel mixture. Unless there is a problem in the wiring or an exhaust leak, replacing the oxygen sensor most likely will fix the problem.
The code P0102 reads "Mass air flow circuit low input". The procedure test for MAF operation.
MAF sensor signal voltage key on engine off, 1 Volt.
Watch the air mass. It should be 4-5 g/s at no-load idle and 150-165 g/s at full load, at 5,500 rpm.
Check the Mass Airflow (MAF) Sensor output on a scanner while driving the vehicle. It should be getting to 133 g/s at Wide Open Throttle (WOT) or more.
Also, look at the self-adaptation factor.
It should be about 1.0. If over 1.15, there is a lean running problem.
Code P0171 reads "System too lean (Bank 1)" and code P0174 reads "System too lean (Bank 2)" What it means is that the engine is running lean. There are many possible problems that may cause the air-fuel mixture to be lean: Defective or contaminated airflow sensor, intake vacuum leak, dirty fuel filter, etc. There are certain tests to be performed to find the exact cause of the problem.
Common problems with Ford engines are defective airflow sensors and vacuum leaks.
A code P0172 may mean that one or more of the following has happened:
The MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of "oiled" air
filters can cause the MAF to become dirty if the filter is over-oiled
There could be a vacuum leak.
There could be a fuel pressure or delivery problem
Possible Solutions
Possible solutions include:
Inspect all vacuum and PCV hoses, replace if necessary.
Clean the Mass Air Flow sensor. Best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling
Inspect fuel lines for cracks, leaks, or pinchesDTC P0420 is "Catalytic System Efficiency Below Threshold". What this means, in a nut shell, is the Three Way Catalytic Converter (TWC) is not working properly. To confirm this, you would need a scan tool. The tech at the Toyota dealership made a good guess. A leaking exhaust could cause the P0420 but the leak would have to be between the TWC and the exhaust manifold.
The OBD Catalyst Monitor tests for the HC conversion efficiency of the catalyst(s) by comparing the upstream HO2S sensors with the Downstream and this test is carried out in a steady state vehicle operation.
There are two methods used by the EECV PCM. In some OBD compliant vehicles built between 1994 and 1996 example Ford Scorpio the PCM carries out a 20 second test, by transferring the closed loop fuel control from the front to the rear sensors. This allows the stored oxygen in the catalyst to expel and after 20 seconds compares their switch-rate with a threshold frequency in a table in memory. If the switch ratio is higher than the threshold in memory then a DTC is stored.
In 1996-on vehicles, the switch rate of the rear sensors is compared to the switch on the front. It follows that if the catalyst is efficient it will be removing HC and HO and the rear sensor will show a slow switch rate compared with the front. By dividing the number of downstream switches with those of the upstream gives a catalyst switch ratio, and a typical threshold is 75%, above which a DTC will be recorded.