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<blockquote data-quote="MTF" data-source="post: 1600807" data-attributes="member: 499"><p>Yes, you are correct more than 3/4 of states require a smog test.</p><p>Turning off rear O2s is old school stuff.</p><p>And won't fool a OBDII state inspection.</p><p></p><p>You are wrong about the price of the PCM with your Vin# and OEM Tune Flashed on it.</p><p>It's around $1,500</p><p></p><p></p><p>Now,</p><p>The PCM does not power the rear O2s it only monitors!!!</p><p>Through micro relays it turns them on and off.</p><p></p><p>This is straight from Ford's Owners website:</p><p></p><p>2012 MY OBD System Operation</p><p>Summary for Gasoline Engines</p><p></p><p>There's a lot of reading here about O2 sensors and the PCM, it's starts on page 51</p><p></p><p>I just quickly copied this,</p><p><u>Page 104</u>:</p><p>Rear HO2S Heaters</p><p>The HO2S heaters are monitored for proper voltage and current. A HO2S heater voltage fault (open, shorted to</p><p>ground, or shorted to battery) is determined by turning the heater on and off and looking for corresponding voltage</p><p>change in the heater output driver circuit in the PCM.</p><p>A separate current-monitoring circuit monitors heater current once per driving cycle. The heater current is actually</p><p>sampled once to three times. Multiple samples are taken for protection against noise on the heater current circuit. If</p><p>the majority of the current samples fall below or above a calibratable threshold, the heater is assumed to be</p><p>degraded or malfunctioning.</p><p>Beginning 2012MY, some PCMs do not have a separate heater current-monitoring circuit (without shunt resistors</p><p>that can directly measure the current through the HEGO heaters). In this case, the sensor heater performance is</p><p>monitored by the "HO2S Heater Impedance Monitor". The HO2S heater impedance monitor measures the HO2S</p><p>internal impedance, validates the measurement, and then compares the validated internal impedance to an</p><p>internal impedance threshold. If the validated internal impedance exceeds the threshold, then the monitor fault</p><p>counter increments once. If the fault counter exceeds the total number of valid internal impedance measurements</p><p>required, a HO2S heater control circuit range/performance malfunction (P00D2/P00D4) will be set.</p><p>Any corrosion in the harness wiring, connector, or increase in the sensor heater element resistance will result in an</p><p>overall increase in the heater circuit resistance, causing the HO2S impedance to increase. The impedance is</p><p>dependent on the HO2S element temperature and the voltage at the connector. As the HO2S element</p><p>temperature increases, the impedance decreases. Furthermore, as the voltage at the connector increases, the</p><p>sensor impedance decreases. Hence, the impedance threshold is a function of the inferred HO2S element</p><p>temperature and the voltage at the connector.</p><p>The HO2S heater impedance monitor runs once per trip; however, it can be forced to run intrusively. When the</p><p>heater is inferred to have been adequately warm, but the HO2S sensor is suspected to be cold because the HO2S</p><p>voltage falls inside the suspected open HO2S circuit voltage fault band or inside the suspected HO2S circuit</p><p>shorted to ground voltage fault band, a HEGO sensor circuit or HEGO heater malfunction is suspected. To</p><p>differentiate HO2S signal circuit failures from a degraded/malfunctioning heater or normal FAOS control, the HO2S</p><p>heater impedance monitor is forced to run intrusively after the heater voltage test and the HO2S open/short to</p><p>ground circuit diagnostics had ran and indicated no malfunction.</p></blockquote><p></p>
[QUOTE="MTF, post: 1600807, member: 499"] Yes, you are correct more than 3/4 of states require a smog test. Turning off rear O2s is old school stuff. And won't fool a OBDII state inspection. You are wrong about the price of the PCM with your Vin# and OEM Tune Flashed on it. It's around $1,500 Now, The PCM does not power the rear O2s it only monitors!!! Through micro relays it turns them on and off. This is straight from Ford's Owners website: 2012 MY OBD System Operation Summary for Gasoline Engines There's a lot of reading here about O2 sensors and the PCM, it's starts on page 51 I just quickly copied this, [U]Page 104[/U]: Rear HO2S Heaters The HO2S heaters are monitored for proper voltage and current. A HO2S heater voltage fault (open, shorted to ground, or shorted to battery) is determined by turning the heater on and off and looking for corresponding voltage change in the heater output driver circuit in the PCM. A separate current-monitoring circuit monitors heater current once per driving cycle. The heater current is actually sampled once to three times. Multiple samples are taken for protection against noise on the heater current circuit. If the majority of the current samples fall below or above a calibratable threshold, the heater is assumed to be degraded or malfunctioning. Beginning 2012MY, some PCMs do not have a separate heater current-monitoring circuit (without shunt resistors that can directly measure the current through the HEGO heaters). In this case, the sensor heater performance is monitored by the "HO2S Heater Impedance Monitor". The HO2S heater impedance monitor measures the HO2S internal impedance, validates the measurement, and then compares the validated internal impedance to an internal impedance threshold. If the validated internal impedance exceeds the threshold, then the monitor fault counter increments once. If the fault counter exceeds the total number of valid internal impedance measurements required, a HO2S heater control circuit range/performance malfunction (P00D2/P00D4) will be set. Any corrosion in the harness wiring, connector, or increase in the sensor heater element resistance will result in an overall increase in the heater circuit resistance, causing the HO2S impedance to increase. The impedance is dependent on the HO2S element temperature and the voltage at the connector. As the HO2S element temperature increases, the impedance decreases. Furthermore, as the voltage at the connector increases, the sensor impedance decreases. Hence, the impedance threshold is a function of the inferred HO2S element temperature and the voltage at the connector. The HO2S heater impedance monitor runs once per trip; however, it can be forced to run intrusively. When the heater is inferred to have been adequately warm, but the HO2S sensor is suspected to be cold because the HO2S voltage falls inside the suspected open HO2S circuit voltage fault band or inside the suspected HO2S circuit shorted to ground voltage fault band, a HEGO sensor circuit or HEGO heater malfunction is suspected. To differentiate HO2S signal circuit failures from a degraded/malfunctioning heater or normal FAOS control, the HO2S heater impedance monitor is forced to run intrusively after the heater voltage test and the HO2S open/short to ground circuit diagnostics had ran and indicated no malfunction. [/QUOTE]
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