'05 GXP - Problems again!

[CMNTMXR57]

The decay rate test with the ignition off.

[rwebb616]

Oh.. you're referring to the one with the car off... I read about it in the AllData service information for my car so I guess it does..

Rich

[CMNTMXR57]

It runs a decay rate test (that is the EVAP test) with it on, not off.

[CMNTMXR57]

And now that I think about what you're saying, let's define "off".

OFF - meaning, you're sitting in your house watching TV with a beer in your hand, keys hanging in the kitchen on the key rack, and it's running an EVAP test? NO, that won't happen.

Or

OFF - meaning, you have the key in the ignition, on accessory (just before you crank it), so the engine is off, but all systems "energized". Then YES, it could be running the test.

[rwebb616]

OFF - meaning, you're sitting in your house watching TV with a beer in your hand, keys hanging in the kitchen on the key rack, and it's running an EVAP test? NO, that won't happen.

I was looking for the section from the service information - this is what it says:

Small Leak Test
The engine off natural vacuum (EONV) diagnostic is the small leak diagnostic for the evaporative emission (EVAP) system. The EONV utilizes the dynamic temperature changes in the fuel tank immediately following a drive cycle to generate natural vacuum or pressure in the fuel tank. While previous leak detection was performed with the engine running, the EONV monitors the EVAP system with the key OFF. The control module will remain active for up to 45 minutes after the engine is turned OFF. The EONV test monitors the fuel tank pressure (FTP) or vacuum as the fuel changes temperature to determine if a leak is present. If the system is truly sealed, there will be a pressure and/or vacuum change as the temperature of the fuel changes. Pressure or vacuum changes that are less than the calibrated values indicate a leak. The EONV diagnostic is designed to detect leaks as small as 0.51 mm (0.2 inches) . The procedure for locating and repairing the EVAP system leaks is the same for the EONV as with the other EVAP systems. If the test reports a falling value, DTC P0442 will set.

That is the one I was referring to.
Rich

[CMNTMXR57]

I'll have to look that up on GMSI. I don't recall GM being that sophisticated to run such a test post ignition cycle. At least on pre-CAN setups anyway. Post-CAN setups, different story.

[rwebb616]

Yeah it might just be a generic section - but it is in AllData DIY that I have for my car. Have to have something like that to do anything nowadays on these cars - and this was 2005!! I can't imagine what these things are doing on current vehicles. Has to be a diagnostic nightmare.

It was under the "Evaporative Emission (EVAP) Control System Description" section which could possibly be generic although it refers to the specific DTCs that it sets.. Not sure how I could verify that it actually does the test - I just had remembered reading about it when I was trying to learn how the system works.

[rwebb616]

Kind of excited now... cleaned up my gas filler nozzle - was really bad .. had to use my dremmel to get the rust off. Put a bit of silicone plumbers grease on it and cleaned the gasket on my cap. It's definitely sealed tight now.

Just finished a 40 mile trip and the EGR test now is listed as complete and "green" .. only two tests that haven't completed now are Catalyst and EVAP..

Pulled codes enroute and once again when I stopped - 0 faults found. Hope this an indication problem solved!

Rich

[CMNTMXR57]

Yup...

[rwebb616]

Now on to the battery - purchased through AutoZone and it has a 5 year warranty with 3 of the 5 being free replacement. Took it back to them and they put their tester on the car and said both alternator and battery are testing fine.

I added the voltage gauge to my Torque Pro display and it's staying right at around 14.8 but when I shut the car off it drops to 12.7. Seems the voltage at rest should be closer to 13.8 yes?

[CMNTMXR57]

No, it's a 12 volt battery. 12.7 is > 12. Really 12 - 13 static is normal.

[rwebb616]

Ok well maybe I have a bad starter relay. When it went to Canada Jake removed the little plastic cover on the relay (#36 in the box) exposing the contacts. He told me that even when there is enough power in the battery to start the car GM has a circuit that doesn't allow it to start if the voltage is below a certain threshold so you might get a "Click" at the key but leaving the key on and manually closing the contacts on the relay cranks the engine and that is what I have been doing each time when the thing won't start with the key. Could perhaps be that the relay got damaged. I'll see if I can get a replacement - those I don't believe are very expensive < $15

[CMNTMXR57]

Fusible links?

[rwebb616]

Fusible links?

How would I check those / where? Oddly the alldata on electrical shows locations of connectors and splice packs but not fusible links.. that seems odd.

It does seem to be power related though because I never have an issue with it after the first start of the day. It's only usually if the car has been sitting all day or overnight then I have the click thing. I do know though that if I charge the battery with an external battery charger it tends to be good for a week or two then starts doing it again. That is what lead me to believe maybe a battery but if they're testing and saying both are good then I don't know. I could take it elsewhere and have someone else test it.

Rich

[rwebb616]

This morning the SES light came back on - pulled the codes and it's a P0174 and a P0171 system too lean both bank 1 and 2 ... the Emissions Readiness tests all have run except the catalyst and passed. Catalyst still shows incomplete.

Exhaust smells rich - car probably compensating for lean condition.

[rwebb616]

Not sure why it's doing this but now after throwing the lean codes the light has gone off but the codes remain - and then the light came back on some time later with the same codes and has since gone off. It seems to be maybe just on the edge or something .. how do I troubleshoot those two codess with a lean condition?
Rich

[CMNTMXR57]

All codes move to a historical file until 40 successful consecutive operating cycles have passed.

[rwebb616]

Cool - any suggestions on troubleshooting?

I have a new fuel filter that was put in a short time ago so I don't believe it to be low fuel pressure. Catalyst readiness test still hasn't completed.

Rich

[CMNTMXR57]

Generally that means you have a post-MAF leak. These N* engines, all rubber boots, gaskets, sleeves, etc after the MAF are points where I would look.

[rwebb616]

Generally that means you have a post-MAF leak. These N* engines, all rubber boots, gaskets, sleeves, etc after the MAF are points where I would look.

Could it be a MAF sensor issue? Not sure how to check/test that.