Thread: P0401 code now...

I "fixed" the P0121 I had by replacing my TPS. This morning I got a P0401 code, which is the EGR. Reading the threads, I suspect that one of the tubes running from the EGR is dirty, but I don't know exactly where on the engine that tube is, and how easy it will be to clean it out. I believe it's behind behind the throttle body, right near the throttle cables. Is this right? and will I need to remove the TB to clean those values, or will removal of the EGR allow for easy removal of the tubes?

It would be really helpful if you didn't assume everyone knows the names of each code off the top of their head. Heck..even a google link to show what the code is would be helpful.

From Google: P0401 Insufficient EGR Flow.

If you assume this to be an EGR issue, you should take a second and do more leg work. The change in flow is monitored and reported by the MAP sensor. Typiecally if the EGR pintle wasn't moving you'd have codes for that as well as flow. If you have only a flow code, you'll want to check the map sensor and then the EGR pintle.

Read this whole thing please
GearChatter.com :: View topic - DTC P0401 Exhaust Gas Recirculation (EGR) Flow Insufficient

I know what the codes are signaling. My question was in regards to cleaning the tube or tubes from the EGR. The codes are intermittent. The P0121 (TPS problem) code has returned, with a week old TPS, but the P0401 (EGR) is gone. So I don't believe there is a problem with the actual electronic pieces - it's possibly a dirty throttle body, and the tube running from the EGR to the TB is blocked or severely limited. I've read a few other threads regarding EGR codes that were the result of dirty tubes, and I wanted to make sure when I took everything off that I clean what can be cleaned.

I've yet to ever find that EGR tube from the EGR to the LIM to be dirty beyond a light layer of exhaust carbon. And by light..I mean very light.

Personally feel like it's an evil polka dotted ostrich hunt you are on with the EGR tube...but here ya go:
The tube location. Find the EGR there are two tubes. One that is part of the EGR bracket, it connects to the exhaust manifold. The other is under the throttle body to the EGR and can be removed seperately.

Let us know what you find. FWIW the codes aren't signaling a dirty tube.

Ok, I have no idea what the deal is now. It might be be a short somewhere. I took off the new TPS I bought and put the old one back on my Grand Prix. I had P0122 (Throttle Position Sensor/Switch 'A' Circuit Low Input) with the new sensor and now with the old sensor, and no P0401. When I first replaced the TPS, I got a P0121 (Throttle/Pedal Position Sensor/Switch 'A' Circuit Range/Performance.), as well as the P0401.

One thing I have noticed is that when I put the new sensor on, it is not lined up perfectly with the two screws, and i have to move the throttle cable a little bit to put the screw in. Is there an adjustment that has to be made that could be causing these P0122 errors? I also tried pulling the TPS off my Impala and putting it on my GP. When I put THAT TPS back on my Impala, I got P0122 errors. With the new TPS on the Impala, it also didn't align perfectly, and P0122 errors exist on it. The old Impala TPS also started giving P0122 errors, so that makes me believe there might be a short, and I ruined the original Impala TPS when I put it in the GP, shorted it, then put it back in the Impala.

Right now I have original TPS on Grand Prix, new TPS on Impala, both with P0122 errors. Original Impala TPS also was throwing P0122 errors as well. The plan now is to get a replacement TPS for the "new" one I now think I shorted and put that on the Impala, to hopefully fix it. Then I have to try to trace the possible short on the GP. I have a voltmeter, but I'm not sure what i need to test and where. I had a problem a few years ago with a spark plug code and a MAF code, and I traced that to a blown fuse. I check several fuses, but I'm not sure which one the TPS is linked to when trying to read the electrical diagram. I may have missed it, because all the ones I checked were good.

Guess I gotta go look up P0122 to help you. Please hold.

P0122 TP circuit low voltage.
Oh... you really want to read the diagnostic aids on this one. I think part of the answer is right in there.
GearChatter.com :: View topic - DTC P0122

Here's P0121, interesting read on why you aren't seeing it again in the Conditions for setting as well as some more great info that eludes to what the problem could be in the diagnostic aids.
GearChatter.com :: View topic - DTC P0121

And if we read up on the P0401 we can make some correlations from P0121 and P0122 to the EGR code, because it can't even run it's test if either of those are set. Here's the 401 info again.
GearChatter.com :: View topic - DTC P0401 Exhaust Gas Recirculation (EGR) Flow Insufficient

Not sure if you read up on this stuff in the first link I tossed at you. I'd honestly suggest it though. When I read through the what is the pcm/system doing, diagnostic aids and conditions for setting.. I think I see some things that should help resolve this. It's a puzzle though..it's not 100% clear.

TPS from your Gimp to your GP should be the same FWIW.
Plus I'd be checking the voltages and grounds.

Yepper, time to get the voltmeter out. Hopefully I'll have a chance this weekend to get a good look at everything. Need to get a fused wire together so I don't blow up the voltmeter first.

Isn't your multimeter fused ? I think they've been fused since about 1930

Today I had a the chance to drive it to work, and I'm hoping the problem I had is related to the P0122 error. Nearly every time I slowed down in traffic, the RPMs would drop below 500, and the car stalled. In rush hour traffic this afternoon, it was quite a pain! I made sure the only code is still the P0122. Checked for freeze information, just in case, but my scan tool says the computer didn't save anything. I'll have the chance for a multimeter test tomorrow morning. I have another new TPS, so I can put it on if that's what the tests show for my Impala and GP.

This morning I installed a new TPS on my Impala. Unlike the other times, I made sure to disconnect the battery. I wanted to eliminate another short. As soon as I reconnected the battery cable after putting in the new TPS, the Impala started on its own! The keys were not even in the ignition. When I pressed the brake, the car died. Freaky. The good news is the SES light was not illuminated, and the scan tool showed the car clear of errors.

I decided to take my bike out for a ride and stopped at a car parts store for another TPS for the GP. Disconnected the battery again, installed the new TPS, and started the car. No SES light, but the scan tool did have a pending P0122 error. I deleted that error, and it did not come back up. Took the GP out to run some errands, no SES return! I hope I'm finished with this. The big lesson I learn from all my trouble is to DISCONNECT THE BATTERY if you're doing anything that has an electrical connection! If I had done that when I first started two weeks ago, I probably would have only needed one new TPS, as the original Impala one would have worked in the GP.