P0141 And P0401

[hillre]

Hello,
I've a 1996 Grand Prix (SE)with a 3.1 engine automatic transmission (212,000 mileage). My service engine soon light is coming on intermittently. DTC codes per my scan tool are P0401 (EGR Flow Insufficient) and P0141 (02 Sensor Heater Circuit Malfunction (Bank 1 Sensor 2). Thus far, I replaced the EGR Valve ($100). Still receiving P0401 code! What should I do next regarding EGR Flow Insufficient? Do I need to remove the throttle body and plenum to see if there is carbon build-up in the intake manifold or any ports, specifically, the port that leads to the EGR valve? If I do remove the throttle body, is it difficult to remove the throttle cable and or do I have to remove the throttle cable prior to removing the throttle body. If I remove the plenum, do I need to install a new intake manifold gasket?
In regards to the P0141, what should I do to eliminate this code? Should I replace the O2 sensor (s), that is after I find them? What exactly is a O2 Sensor Heater or is this part of the O2 sensor itself. Please tell me what is the meaning of "Bank 1 Sensor 2)? By the way, I have never replaced the O2 sensor (s) on this vehicle. Maybe it time to do so ha. Another question, if the O2 sensor(s) are faulty, could this create a code within the EGR system? Sorry for all the questions! I'm just desperate for HELP because I don't want to take vehicle to a shop if I can prevent from doing so.
I would really appreciate any suggestions and or recommendations that anyone may have from your experience with these type DTC codes.

Happy Holidays!

[BNaylor]

Check all vacuum lines at the throttle body, intake manifold, purge solenoid, fuel pressure regulator and the MAP sensor. The ECM/PCM module uses MAP to run the EGR flow test.

If you remove the UIM it will be 50/50 as to whether you will need new gaskets. They will probably not stay intact to I would recommend getting new UIM gaskets. Also, I hope you put in a new EGR valve gasket.

The Bank 1 Sensor 2 means the rear after CAT convertor 02 sensor. I would resolve the 02 sensor problem first. Remove the 02 sensor and inspect first. Clean with carb or throttle body spray cleaner. Make sure receptor vanes are free of carbon.

Also, you should check the 02 sensor heater voltage at the electrical connector. If present then the 02 sensor is probably bad.

[richtazz]

Most if not all OBD-II cars have heated o2 sensors. The heater allows the sensor to come up to temp quicker, so the car can go into closed loop mode sooner reducing emissions. The code you're getting is normally indicative of a bad sensor, especially with your mileage. Just make sure you don't buy a Bosch brand, as their heated sensors are JUNK.

The p0401 code is tricky. I know that in the 3800 engine, a vacuum leak near the MAP sensor/PCV valve will trip this code, as the PCM uses MAP sensor vacuum signal to test EGR efficiency. The 3.1 has a different set-up, and I'm not sure if it uses the same test. The first thing I would check is the tube that runs from the rear exhaust manifold to the EGR for carbon build-up. If it's clear, then the next thing I would look for is a cracked/disconnected vacuum hose/tube or a vacuum leak.

[hillre]

Thanks for the info, I appreciate it.

Originally Posted by richtazz

Most if not all OBD-II cars have heated o2 sensors. The heater allows the sensor to come up to temp quicker, so the car can go into closed loop mode sooner reducing emissions. The code you're getting is normally indicative of a bad sensor, especially with your mileage. Just make sure you don't buy a Bosch brand, as their heated sensors are JUNK.

The p0401 code is tricky. I know that in the 3800 engine, a vacuum leak near the MAP sensor/PCV valve will trip this code, as the PCM uses MAP sensor vacuum signal to test EGR efficiency. The 3.1 has a different set-up, and I'm not sure if it uses the same test. The first thing I would check is the tube that runs from the rear exhaust manifold to the EGR for carbon build-up. If it's clear, then the next thing I would look for is a cracked/disconnected vacuum hose/tube or a vacuum leak.

[hillre]

Thanks very much sir!

Originally Posted by bnaylor

Check all vacuum lines at the throttle body, intake manifold, purge solenoid, fuel pressure regulator and the MAP sensor. The ECM/PCM module uses MAP to run the EGR flow test.

If you remove the UIM it will be 50/50 as to whether you will need new gaskets. They will probably not stay intact to I would recommend getting new UIM gaskets. Also, I hope you put in a new EGR valve gasket.

The Bank 1 Sensor 2 means the rear after CAT convertor 02 sensor. I would resolve the 02 sensor problem first. Remove the 02 sensor and inspect first. Clean with carb or throttle body spray cleaner. Make sure receptor vanes are free of carbon.

Also, you should check the 02 sensor heater voltage at the electrical connector. If present then the 02 sensor is probably bad.

[BNaylor]

Originally Posted by richtazz

The p0401 code is tricky. I know that in the 3800 engine, a vacuum leak near the MAP sensor/PCV valve will trip this code, as the PCM uses MAP sensor vacuum signal to test EGR efficiency. The 3.1 has a different set-up, and I'm not sure if it uses the same test.

Similar test and same parameters. MAP is used on the 3.1L/3100 too for the EGR flow test. Difference is on a 3800 P0401 is most likely caused by a missing o-ring on the PCV valve. But not in this case.

[hillre]

Sir,

What do you mean by "Purge Solenoid?" I'm not familiar with such term. Thanks

Originally Posted by bnaylor

Similar test and same parameters. MAP is used on the 3.1L/3100 too for the EGR flow test. Difference is on a 3800 P0401 is most likely caused by a missing o-ring on the PCV valve. But not in this case.

[BNaylor]

Originally Posted by hillre

Sir,

What do you mean by "Purge Solenoid?" I'm not familiar with such term. Thanks

It is used for evaporative emissions and has a vacuum line connected to it. Located on the right hand side of your throttle body (TB). Between TB and EGR valve. Check the vacuum line connections to it but it is probably not causing the P0401 code.

Final note: Based on your symptoms of both EGR and 02 sensor acting up I would not rule out a restricted exhaust system or clogged CAT. This is the last item recommended for inspection by the GM service manual if all else fails. Good luck.

[richtazz]

Thanks for the clarification on that Bob. I figured the parameters were the same, but didn't want to state as fact unless I knew for sure. The PCV o-ring on the 3800 causes a vacuum leak, whereas the 3100 has a different arrangement, but I was 99% sure that a vacuum leak to the MAP would cause the same code on the 3100.

[hillre]

FYI,

I would like to thank you for the assistance. I finally took time to remove the throttle body to see if there were any clogged ports. I found the problem as soon as I remove the throttle body. The port leading to the EGR valve was very clogged. The carbon had accumulated so much that it looked like a ball of rubber and or asphalt. I cleaned the port with carb cleaner. Had to use a clothe hanger to penetrate the carbon by running it through the port beneath the EGR valve. I didn't noticed any other carbon buildup except for the plate of the throttle body. I certainly hope that I removed all of the carbon to prevent the MIL from coming on again. Now I understand why the scan tool was telling me "insufficient EGR flow." I noticed that the port that was clogged is very small in diameter. I was expecting it to be larger. Thanks again! Take Care!

Originally Posted by bnaylor

Check all vacuum lines at the throttle body, intake manifold, purge solenoid, fuel pressure regulator and the MAP sensor. The ECM/PCM module uses MAP to run the EGR flow test.

If you remove the UIM it will be 50/50 as to whether you will need new gaskets. They will probably not stay intact to I would recommend getting new UIM gaskets. Also, I hope you put in a new EGR valve gasket.

The Bank 1 Sensor 2 means the rear after CAT convertor 02 sensor. I would resolve the 02 sensor problem first. Remove the 02 sensor and inspect first. Clean with carb or throttle body spray cleaner. Make sure receptor vanes are free of carbon.

Also, you should check the 02 sensor heater voltage at the electrical connector. If present then the 02 sensor is probably bad.

[hillre]

FYI,

I would like to thank you for the assistance. I finally took time to remove the throttle body to see if there were any clogged ports. I found the problem as soon as I remove the throttle body. The port leading to the EGR valve was very clogged. The carbon had accumulated so much that it looked like a ball of rubber and or asphalt. I cleaned the port with carb cleaner. Had to use a clothe hanger to penetrate the carbon by running it through the port beneath the EGR valve. I didn't noticed any other carbon buildup except for the plate of the throttle body. I certainly hope that I removed all of the carbon to prevent the MIL from coming on again. Now I understand why the scan tool was telling me "insufficient EGR flow." I noticed that the port that was clogged is very small in diameter. I was expecting it to be larger. Thanks again! Take Care!

Originally Posted by richtazz

Thanks for the clarification on that Bob. I figured the parameters were the same, but didn't want to state as fact unless I knew for sure. The PCV o-ring on the 3800 causes a vacuum leak, whereas the 3100 has a different arrangement, but I was 99% sure that a vacuum leak to the MAP would cause the same code on the 3100.