code 401

yes, i replaced the egr valve and the this code appeared. it seems to happen everytime at the same place on interstate when decending down a grade with no acceleration.

Please post the year and engine size. This will help us with a diagnosis of your problem.

engine size 3.8 non turbo & 1997 gp se

Typically DTC P0401 is a EGR flow issue but not the EGR valve. Issue with engine vacuum and manifold absolute presssure (MAP) which is used to test EGR flow when called upon.

Was the PCV valve replaced lately? Check to make sure you have the o-ring installed on the PCV valve located at the right side of the UIM on a NA SII 3800 engine.

yes, im still having problems with these codes appearing. i hooked up to computer and this is the information that appeared. the car was at idle.
(1) absolute throttle positon 0%
(2) engine rpm 729
(3) calculated load level 15%
(4) time advance cyl 1 21%
(5) intake manifold pressure 15.9 in. hg
(6) air flow rate (maf sensor) .4 lb/min
(7) fuel system 1 status closed loop
(8) fuel system 2 status unused
(9) short term fuel trim (bank 1) + 20.3%
(10) long '''''''''''''''''''''''''''''''(bank 1) +16.4%
(11)intake air temp 80 f.
(12) coolant temp 186F
(13) o2 sensor 1 bank 1 0.03v@+20.3 st fuiel trim

these are the codes on car at this time and sometimes code 171 also appears.

thank you

The short and long term fuel trims are way off possibly indicating you have a vacuum leak or an issue causing the fuel injection system to overly compensate for either a lean or rich condition. The P0420 DTC is a CAT converter efficiency issue.

Have you run an engine vacuum test with an automotive vacuum gauge 0-30 in-hg?

DTC P0171 indicates the system is in a lean trim mode. Ideal fuel trim = zero. Greater than zero (+) indicates the PCM is adding fuel to compensate for the lean condition. If fuel trim is less than zero (-) the PCM is reducing the amount of fuel to compensate for a rich condition.

thanks for the reply bill naylor, one more question where would i hook up to take vacuum test and what reading is normal? If any one would have a diagram where to hook up would be very helpful

You can connect the gauge to the HVAC accessory vacuum line right off the line that feeds the brake booster (back of UIM plenum) or right off the lines you see on the throttle body that feed the purge solenoid or fuel pressure regulator. Reading will be around 15-22 in-hg (green area). Check at idle and at 2000 rpms. On a NA SII 3800 engine with no vacuum leaks, no issues and good UIM and LIM gaskets, etc. you should see around 16-18 in-hg at idle. At 2K rpms vacuum reading will vary but stay at around 18 in-hg or higher once stabilized. If this reading drops off towards low end of range or towards zero then the CAT converter is suspect. Let us know how the readings turn out. Good luck.

Also, did you check the PCV valve and o-ring?

thanks for the help b naylor and will post of the outcome after i get a vacuum gauge

hello, i been so busy just had time to hook up vacuum gage and the readings are at idle 20 and at 2k approx 22. the car is still throwing codes 171,401, 420. sorry im just finally getting to post all help will be appreciated

Vacuum test looks good but not conclusive I guess. Do you still have the original upper and lower intake manifold gaskets? Did you check the PCV valve and o-ring? The P0420 DTC is normally a bad CAT converter. Oxygen storage capability is less than satisfactory.

hello thanks for the reply b naylor, the motor has never been touched still original upper and lower intake manifold gaskets. i replaced the o'ring and new pvc valve also. could the cat converter be causing all of these problems?

Just to clarify, did you replace both the lower black o-ring that goes on the PCV valve itself as well as the larger orange o-ring at the top of the housing?

Have you inspected the little corrigated orange seal on the MAP sensor to be sure you don't have a vacuum leak there since the MAP sensor vacuum reading is much lower than the actual vacuum readings you got on your guage?

Are you experiencing any mysterious coolant loss?

Other than the code popping up, is the car running fine including both part throttle and during hard acceleration?

Based on the symptoms and at face value I would say whatever the cause is it looks like it is common to all 3 DTCs so just to be sure check the 12 volts that feeds the pre and post CAT converter 02 sensors and the EGR valve. It comes from IGN MAIN 1 - UH which is there at Ignition to ON. Also, there is a fuse marked IGN MAIN 1 - UH in the engine compartment fuse box.

Or it may not be and there is more than one problem in which each will have to be looked at individually starting with the easy.

thanks every one for the help i will look at the pcv valve and housing o"rings.

about the coolant loss approx. erery two weeks, a small amount is needed because the low coolant light come on.

Unless you see visible external leaking it sure sounds like your intake gaskets. Do you have any sludge in the cooling system or coolant in the oil or crankcase? Look at the back of the oil filler cap for condensation or signs of coolant and in the radiator at the filler neck and radiator cap for sludge. And at the coolant reservoir?

Do you know if the plastic upper plenum has ever been replaced? There is a known issue with the EGR stovepipe causing the UIM to warp and leak coolant. Since this is around the area that feeds the EGR gasses into the intake stream, it could also be causing your EGR flow codes.

thanks for the reply everyone, there is no coolant in the oil, no yet. there is a small oil pocket laying on the front of engine approx mid way on the manifold, if this will help,but no oil in coolant.

Are you sure it is oil and not coolant? Coolant will look black or turn black after sitting there awhile and baking on the lower intake manifold.

it sure looks like oil, any way to tell for sure by visual test?

The big question is if it is motor oil how did it get there? I am assuming you are referring to the stuff collecting at the lower intake manifold port runners and the area where the fuel injectors are located. In most cases it would be bad lower intake manifold port gaskets or even a bad UIM gasket so check those areas carefully. BTW - No oil flows through the UIM unless you have a bad PCV valve and it gets in via the PCV part of the UIM.

What condition are your valve cover gaskets in? Even if they are bad the oil will not go to that area but drip or settle at the area of the exhaust manifolds.

i checked the o'rings on pcv housing and pcv valve. no o'ring on pcv valve. i purchased the kit at gm. it included pvc valve and spring and orange o' ring. should the pvc valve have a o'ring on it. maybe this is the problem?

As previously mentioned the PCV must have the black o-ring on it. See pic. This should take care of at least the P0401 EGR flow DTC. After corrective action just reset the DTCs and then after a few drive cycles see if at least the P0401 DTC clears.

http://macgp.clubgp.com/howto/engine/pcv/GT/DSCF0012.jpg

While you're in there replacing that o-ring on the pcv valve, look at the black plastic elbow that goes from the lower intake to the belt tensioner (located just below the PCV/Map housing). If it's wet around there, that may be the source of your coolant loss too. They can seep coolant, but not enough to end up on the ground.

thanks again for the help about o'ring on pcv vale. will try and let you know results.

yes, i put a new o'ring on pcv valve and the 171 & 401 code has stopped, but code 420 is still hanging around. when the check engine light comes on with this code, it will light up light and sometimes after shutting down engine and , the light will turn off. Is this common or should it stay on till reset? thanks for all the help everyone