'05 GXP - Problems again!

[rwebb616]

Ok so now the saga continues with my 05. Back in October of 2019 I had the engine rebuilt by Northstar Performance out of Canada. Fast forward a couple of years and about 20,000 miles and I'm now having some serious issues with the car again. I'm not sure what to do but it's acting very weird. Here are the symptoms:

1. Check Engine light on - I knew about an O2 / Cat code that I had previously read/cleared but had not gotten around to having it checked out
2. Charging system issue - brand new battery over about a week or two's time will drain to the point where the car will click when attempting to start but I can then start by manually tripping the relay under the hood - so enough voltage to start but not enough apparently for the computer. Alternator was replaced by Northstar Performance at engine rebuild time.
3. Took it in to check out the O2 sensors and the cat and they pulled the codes and I have a number of codes dealing with things from Transmission long shift to engine running lean, evap leak etc.
4. They cleared all the codes to start fresh and upon starting the car all the previous codes come immediately back. This should not be happening according to the tech - especially the transmission one since the car was not put in gear nor moved. They cleared at least 3 times and had the same response from the computer - all codes came immediately back.
5. I have seen indications on the DIC display about "Service Security System" and "Service Stability System" both of which seem to be working

They are now at the point where they "suspect" the PCM but they're not even sure about that. He's not even sure there is a problem with the car since the computer is acting so weirdly.

Has anyone had anything like this or could shed any light on the issue?

Right now I'm leaning towards a PCM replacement but not entirely sure what to do. I've put a bunch of money in getting the engine rebuilt so I really would like to keep the car but electrical problems can be hard to find/fix. The car is a daily driver and (heated) garage kept so hasn't been sitting for any length of time. As far as the engine the car seems to run fine - the exhaust smells maybe a little rich - it uses a bit of oil but I'm told by Jake that this is normal for a Northstar.

-Rich

[CMNTMXR57]

PCM replacement is usually the last step. Sounds like something in the harness is shorting out somewhere, especially with battery drain like that.

The codes coming back immediately after clearing, means it's an I/M system test (readiness monitor) that is failing. GM instructs the PCM to keep running that particular test until it passes. So you can clear the code all you want, as long as the particular fault is there, it'll keep flagging as soon as you clear.

[rwebb616]

PCM replacement is usually the last step. Sounds like something in the harness is shorting out somewhere, especially with battery drain like that.

That doesn't sound fun but it makes a lot of sense since when I got the car back and it threw the code I was able to clear it at that point so perhaps there is a loose connection point or corrosion build up somewhere. The code eventually (after a day or two) came back but I had not checked it again - just planned to get it in at some point. Well some point has arrived and now this.

Are there well known locations that corrosion builds up or places that are common to check?

means it's an I/M system test (readiness monitor) that is failing.

Sorry - what does I/M mean ?

Rich

[CMNTMXR57]

The one thing I would be concerned about, when they did the engine work, on the back side of the engine is the main harness. It's really tight against the cam covers/head. I would look there for something pinched, shorted out, connector terminals pulled out somewhere, etc...

I/M = Inspection and Maintenance monitors. Your PCM will run random tests behind the scenes to see that certain functions are online and functioning. If one passes, it moves on to the next. If it fails, it keeps running it until it passes.

These are some of the parameters that can be an I/M test. Each platform, each year can have different parameters.

[rwebb616]

I relayed this information to the shop that is working on it - THANK YOU!

One thing I forgot to mention is that he said that he keeps losing connection to the computer so this also points to a possible electrical short. I told them what you said about the main harness and authorized a couple of hours of work to see if they can locate the issue so hopefully it's something easy to find/fix.

Rich

[rwebb616]

*sigh* well they spent 2 hours looking around inspecting the harnesses and everything they can see looks good - no signs of pinched wires or anything like that - maybe time for a trip to the dealer? I do have AllData so I could start going through the wiring harness and see if I can troubleshoot what I can myself.

Only charged me 1 hour of labor for about 4 hours of time but at this point they're not really sure what to tell me next. They said they checked on a new PCM for it and found one for $350 but it indicates in their book that it needs to be programmed for the car so not inclined to go that direction until a much more exhaustive harness search has been completed I think. A short really makes sense with all the issues that are happening.

Any other ideas?

Rich

[CMNTMXR57]

Yes, they need to be programmed to the car and a crank relearn done.

I mean, kinda hard to troubleshoot electrical issues when you have the car in front of you, even harder over the intertubez. I would look for bad grounds, things grounding out that shouldn't, etc...

In that harness, it is a wire bundle. If something has rubbed through, the tape/protections of it, that would be an issue.

[rwebb616]

I know you said PCM is last resort - could it just be one of those I/M tests that are failing - maybe something there needs to be addressed before anything else? That doesn't explain why connections with the computer are dropping though. Sounds like your gut instinct is telling you that it's a short. So my options at this point appear to be:

1) Tear into it myself not knowing exactly what I'm doing - just plan to track down every connection and do continuity tests etc following diagrams from Alldata.
2) Take it to the dealer - not sure I trust them to have someone qualified enough to do the work - always my concern when you're paying higher labor prices - probably a Cadillac dealer since it's Northstar.
3) See if I can locate someone REALLY good at diagnosing these things with the proper equipment.
4) Run it as-is and hope it doesn't get worse - not really an option for me.

My observation is just that things appear to be degrading - most subsystems are working properly - having no issues with lights/audio/horn/alarm etc. Getting messages on the DIC display indicating issues with Gas Cap, Stability System, Security system.

I'm in Michigan - anyone know a top notch diagnostics guru in Michigan?

Rich

[CMNTMXR57]

There is always a hierarchy in code diagnosis. But it's not always the same, so I can't tell you which to tackle first. If you list the codes you are getting, I can give you an order I would suggest.

I would find someone good in electrical diagnosis if you're not comfortable. A dealer probably won't really know much on this engine/car anymore as it's probably been awhile since they've seen one come through for warranty work (dealerships do very little of customer pay service, the bulk is warranty claim issues), which means it's been at least a decade since one of these has come in for anything... Not to mention they're going to be expensive.

Do you have emissions testing where you're at? If so, then you will need to fix this. The I/M failure will fail you the second they hook up.

[rwebb616]

Ok, here are the codes from the computer in order as they display on Torque (all I have to read/reset)

P0171 - Powertrain System Too Lean (Bank 1)
P0174 - Powertrain System Too Lean (Bank 2)
P0420 - Powertrain Catalyst System Efficiency Below Threshold (Bank 1)
P0455 - Powertrain Evaporative Emission Control System Leak Detected (gross leak, check fuel cap, piping etc)
P0507 - Powertrain Idle Control System RPM Higher Than Expected
P0442 - Powertrain Evaporative Emission Control System Leak Detected (small leak)

Well all powertrain related. Didn't have any issue getting the codes - it didn't seem to disconnect on me.

Rich

[CMNTMXR57]

P0455 drives or is simultaneous with P0442, which drives the P0171/P0174 codes, which generates the P0420, which drives P0507 as the PCM is trying to compensate and establish an idle to keep it running.

So I would start with 455/442.

[rwebb616]

Could rusty gas lines have anything to do with this? I noticed when I had to do the brake lines a while back that the fuel lines might be next in line. I also just read in another thread about a guy that had to do a repair on the filler neck of his gas tank..

[CMNTMXR57]

No, just because they're rusty, doesn't mean that they're getting air in, because if they were getting air in, they'd be leaking fuel too. However, if they're that bad, the lines could be clogged, filter clogged, etc... Lack of fuel would cause a lean code too.

EVAP issues are your Purge solenoid, purge valve, gas cap, or other vacuum leak in the EVAP system.

[rwebb616]

Well, I'm not sure what that shop was talking about. I cleared the codes and the computer looks to be doing it's job just fine. I drove at least 10 miles to my first stop today with no check engine light and according to Torque the computer was performing the I/M readiness tests as it should be doing. Kept connection the entire time. This entire thing might be centered around the EVAP system. I spent some time reading on alldata on the systems involved to educate myself... looks like they recommend a smoke machine - not sure if that's required or not but I figured I would at least visually inspect everything and do the simple stuff first.. plan on cleaning the filler opening with a wire brush and getting a new gas cap since it looks a bit rusted. Don't know if this whole thing could be caused by a bad seal on the cap but easy to identify and fix problem.

Without a smoke machine do you know how I could possibly test the other components?

[CMNTMXR57]

I thought you were having other issues though that were electrical?

Yes. The smoke machine is needed to test for the leaks, but can be especially useful if your scan tool has bi-directional controls and you can tell the PCM to open the Purge valve. There is a relationship between the purge valve and purge solenoid. When you command the purge valve open, the purge solenoid should be closed. Vice versa if you command it the other way. Introducing smoke, will tell you if one of those isn't working as smoke will come out where it shouldn't. Someone here posted a DIY smoke machine awhile back, might search for that.

However, lets start simple. Gas cap. Simply sanding down the filler neck end where it seats to the gas cap and putting a light coating of grease on it as well as the rubber o-ring on the cap, can seal it. Again, look for simple things first.

[rwebb616]

Yes, battery drain - I'm not sure if it's a charging issue or drain issue. I read somewhere that besides an alternator there is a voltage regulator somewhere - maybe that needs replacing? I am not sure where the volts gauge should sit in normal operation but it's north of 14v. My brother at one point put his tester on it and it said that it was overcharging but took it to one of those auto places and they said it was not so I'm not sure what the scoop is... I do notice that when something kicks in it drops down to around 8v and then when it kicks back off goes back up to the same spot above 14. I think it's the A/C compressor kicking in and out.

Yeah I read that on the operation of the solenoid/valve - seems simple enough - I don't think Torque is bi-directional that I know of. I just went out to grab some lunch - SES light still off - checked i/m tests and Secondary air system had completed but Catalyst and EVAP and one other one are still incomplete.

Rich

[CMNTMXR57]

The voltage regulator is internal to the alternator. If you're A/C compressor is drawing it down that much, that ain't right. A momentary drop, but almost instant return to normal after initial engagement, fine, but if it drops and stays around that, that's not right.

I/M status as "incomplete" means it hasn't run the test for the monitors you have. That can be a good thing I suppose because if something failed, the PCM would try to run it again after your reset and keep trying to run until it passes. So if it's "incomplete" that means it hasn't failed either. One of those "no news is good news..." kinda things.

Just so you know, the PCM isn't constantly running all those tests. It'll run them randomly based on some operational parameter is detects to kick it off. It'll run and either pass/fail. And again, if it fails, it'll keep running it constantly until it does pass. There are ways under the "Service Bay Tests" section of GMSI that you can run with a Tech2 attached to trick them (that particular diagnostic), in to running. But if you drive it enough, usually within a day or two, a 100 miles or so, they should all run.

[rwebb616]

I mispoke on the battery gauge - the lowest marking on it is 8v and next is 14v and there is a tick halfway inbetween so that must be 11v .. so it drops to around 11v and stays for about 2 seconds then goes back up but I didn't notice that today. I'm not using the air but I know it still cycles because I can hear the relay kicking in and out.

On the battery if I disconnect the ground and put a charger on it overnight it will not give me any trouble for about 2 weeks or so - so it seems like it is charging somewhat but maybe not enough but the volt gauge is showing over 14v so I am lost.

After driving a couple of places I pulled the codes again and I have the bank 1 and 2 too lean codes in a "pending" status so the SES light still isn't on yet. The evap, catalyst and egr tests are still shown as incomplete so apparently they haven't fired yet - or there is the one that I was reading about that does part of it's testing with the car off as it monitors the temperature and pressure of the gas tank.

[CMNTMXR57]

Well that's good. The way you made it sound was that it was killing the accessory drive upon engagement. Your HVAC system will use the A/C Compressor in any defrost/defog mode also. So if you have it set to that, it'll cycle on/off.

Could just be that your battery is getting weak. Sounds like the alternator is doing it's thing.

I don't think the PCM in that car is that complicated to do that type of a test.

[rwebb616]

I don't think the PCM in that car is that complicated to do that type of a test.

Which test do you mean?