GEN 1 P0161 check engine light

[B E N]

Short of replacing the PCM you can turn off the rear O2 code reporting through a number of different tuning platforms. It isn't the right way, but replacing a PCM seems a bit silly.

 

[raptorbone]

Short of replacing the PCM you can turn off the rear O2 code reporting through a number of different tuning platforms. It isn't the right way, but replacing a PCM seems a bit silly.

There are ways to do this, but, at least in Texas, this will return a Not Ready status from the emissions system during inspection. I know this from experience. The problem has to be fixed if, in some states, you wish to register your vehicle. Luckily, PCMs are not expensive, and I don't understand why the heater is powered by the PCM.

 

[MTF]

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,
Page 104:
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.

 

[raptorbone]

Correct, the PCM monitors the health of the O2 sensor heater as a function of voltage. The above post does not address the power source, which, according to the wiring diagram, is the PCM. If you can find something otherwise, we would appreciate seeing it. In my case, I found increased resistance to ground through the common wire when comparing bank 1 and 2 circuits, so I'm still holding out hope it's a circuit fault in the harness.

Impedance is incorrectly used though; applies only to AC circuits.

 

[MTF]

I can tell you that a lot of owners that put on headers started get all kinds of O2 sensor errors.
Through many tries of fixing their issues the one common fix was to replace the O2 wire harness and protect them heat.
Copper wires will build up there own resistance when they become degraded, corroded, oxidized, overheated, etc...

About that impedance statement, you'd have to talk to the Ford engineers who wrote that.

 

[B E N]

There are ways to do this, but, at least in Texas, this will return a Not Ready status from the emissions system during inspection. I know this from experience. The problem has to be fixed if, in some states, you wish to register your vehicle. Luckily, PCMs are not expensive, and I don't understand why the heater is powered by the PCM.

There are 7 options for any error code report in the Copperhead system. In this config my truck will pass a full emissions inspection in Denver, including the MIL test. I do not however have the rear O2 sensor failure you do, so I can't speak to that. I had forgotten they were off in the tune when I went in for emissions. We will see how it goes this next year, since Colorado has once again tightened its emissions standards.

 

[B E N]

And won't fool a OBDII state inspection.

Seriously man, you need to stop talking about the limitations of tuning. You admitted yourself you have no experience working on the copperhead.

And yes, the PCM powers the sensors.

 

[MTF]

Ummmm, Maybe I should have added "per say" for you, after the PCM does not power the O2s in the first sentence.
And If you read my comment completely, I also stated that the "PCM powers the O2s through micro relays".
I'm getting this info directly from Fords ODBII Operation Summary.

You can turn off the rear O2s and stop the engine lamp from coming on.
But, they will never become a ready state for a OBDII state inspection,
I have yet to see anyone bypass this, any make or model.
This is why they make O2 spaces.
O2 simulators do not work for PCM OBD II, but they work on old ECM OBD I

And I'm a little confused, what limitations did I refer to?
Plus I'm only trying help here.

 

[raptorbone]

BEN...good stuff. I use VCM Editor myself but hadn't tried that. Thank you for the suggestion and the wiring diagram.

 

[mike3605]

All good stuff - thanks everyone. I will report back what I find out! Ben, do you have the other pages to that diagram so I can chase these wires?