2004 Gt P0141 And P0161 Error Codes

michaelowen9019 · May 15, 2017

I recently purchased a 2004 GT. It failed the local emissions inspection with the P0161 and P0141 error codes. I replaced both rear O2 sensors and drove it through a cycle. The MIL and codes did not go away. I can reset them with my scanner but they come right back after a few minutes of driving. I have taken it to a couple of repair shops with no results. Any idea what would cause both codes to occur simultaneously, and consistently? The car does not have mufflers. One of the shops told me I wasn't getting enough back pressure to properly heat the sensors.

wmburns · May 15, 2017

michaelowen9019 said:
One of the shops told me I wasn't getting enough back pressure to properly heat the sensors.

Total Hog Wash! Run as fast as possible from this shop. Never go back. An embarrassment to the profession.

The DTC calls out a "circuit malfunction". Anytime the PCM calls out a circuit malfunction that means there's something sooooooo wrong with the circuit at a basic level that the PCM is unable to run any tests upon the circuit. Think:

total sensor failure
connector problem such as corrosion, water, bent/pushed pins.
wiring fault or wiring harness damage. Short between signal lines, ground fault, short to power, open circuit
bad PCM

michaelowen9019 said:
Any idea what would cause both codes to occur simultaneously, and consistently? The car does not have mufflers.

With a circuit malfunction the PCM would set the DTC code almost at key on. So if looking for a common point of failure I would start with a through visual inspection of the wiring harness leading to both rear O2 sensors. Since exhaust modifications have been done I would look for evidence of the harness touching hot exhaust parts.

Another option could be IF the type of O2 sensors were used with a "roll your own pig tail", then look for a wiring/connector error. IE the O2 wires connected to the wrong connector pins.

Finally. Take those brand new rear O2 sensors and move them to the front where they can do some good. The rear O2's are only used to monitor the cats. Whereas the front O2 sensors will improve how the motor will run.

From Ford Manual:
P0141 - HO2S Sensor Circuit Malfunction (HO2S-12)
P0161 - HO2S Sensor Circuit Malfunction (HO2S-22)

Short to VPWR in harness or HO2S.

Water in harness connector.

Open VPWR circuit.

Open GND circuit.

Low battery voltage.

Corrosion or poor mating terminals and wiring

Damaged HO2S heater.

Damaged PCM.

michaelowen9019 · May 30, 2017

wmburns said:
Total Hog Wash! Run as fast as possible from this shop. Never go back. An embarrassment to the profession.

The DTC calls out a "circuit malfunction". Anytime the PCM calls out a circuit malfunction that means there's something sooooooo wrong with the circuit at a basic level that the PCM is unable to run any tests upon the circuit. Think:

total sensor failure

connector problem such as corrosion, water, bent/pushed pins.

wiring fault or wiring harness damage. Short between signal lines, ground fault, short to power, open circuit

bad PCM

With a circuit malfunction the PCM would set the DTC code almost at key on. So if looking for a common point of failure I would start with a through visual inspection of the wiring harness leading to both rear O2 sensors. Since exhaust modifications have been done I would look for evidence of the harness touching hot exhaust parts.

Another option could be IF the type of O2 sensors were used with a "roll your own pig tail", then look for a wiring/connector error. IE the O2 wires connected to the wrong connector pins.

Finally. Take those brand new rear O2 sensors and move them to the front where they can do some good. The rear O2's are only used to monitor the cats. Whereas the front O2 sensors will improve how the motor will run.

From Ford Manual:
P0141 - HO2S Sensor Circuit Malfunction (HO2S-12)
P0161 - HO2S Sensor Circuit Malfunction (HO2S-22)

Short to VPWR in harness or HO2S.

Water in harness connector.

Open VPWR circuit.

Open GND circuit.

Low battery voltage.

Corrosion or poor mating terminals and wiring

Damaged HO2S heater.

Damaged PCM.

michaelowen9019 · May 30, 2017

wmburns said:
Total Hog Wash! Run as fast as possible from this shop. Never go back. An embarrassment to the profession.

The DTC calls out a "circuit malfunction". Anytime the PCM calls out a circuit malfunction that means there's something sooooooo wrong with the circuit at a basic level that the PCM is unable to run any tests upon the circuit. Think:

total sensor failure

connector problem such as corrosion, water, bent/pushed pins.

wiring fault or wiring harness damage. Short between signal lines, ground fault, short to power, open circuit

bad PCM

With a circuit malfunction the PCM would set the DTC code almost at key on. So if looking for a common point of failure I would start with a through visual inspection of the wiring harness leading to both rear O2 sensors. Since exhaust modifications have been done I would look for evidence of the harness touching hot exhaust parts.

Another option could be IF the type of O2 sensors were used with a "roll your own pig tail", then look for a wiring/connector error. IE the O2 wires connected to the wrong connector pins.

Finally. Take those brand new rear O2 sensors and move them to the front where they can do some good. The rear O2's are only used to monitor the cats. Whereas the front O2 sensors will improve how the motor will run.

From Ford Manual:
P0141 - HO2S Sensor Circuit Malfunction (HO2S-12)
P0161 - HO2S Sensor Circuit Malfunction (HO2S-22)

Short to VPWR in harness or HO2S.

Water in harness connector.

Open VPWR circuit.

Open GND circuit.

Low battery voltage.

Corrosion or poor mating terminals and wiring

Damaged HO2S heater.

Damaged PCM.

Thanks for the info. Everything seems good at the O2 connectors. Limited space because of the transmission is keeping me from checkingout the rest of the harness wiring. Is there a trick to removing the harness without removing the transmission? How do you check the PCM?

wmburns · May 30, 2017

In general it's usually best to rule out everything else before going to bad PCM. Swapping a PCM for diagnostic purposes often creates as many problems as it solves.

The exception to this might be IF there was arc welding done on the exhaust system and the work was done taking the proper precautions.

The other low tech method to check for a bad PCM is to perform a visual inspection of the PCM circuit board itself. Look for burnt components or missing printed circuit foil traces.

It's possible to test the wiring harness without removing it. Do you have a Volt-Ohm meter (VOM) and are you willing to use it? If so a series of wire tests looking for shorts to ground or shorts to VPWR would be a great place to start.

If no problems found, then the tests get more difficult. IE using the VOM to "ring out" the individual wires from the O2 connector to the PCM. This will require that the PCM be removed.

When the testing gets to this level a full set of Ford wiring diagrams and service manual is often a big help. If interested in getting a set for yourself I maybe able to help. PM if interested.

2004 Gt P0141 And P0161 Error Codes

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