Chasing the Gremlin

1901 Views 9 Replies 3 Participants Last post by gnonyx, 7 mo ago

gnonyx

Since last years I have been chasing some fault codes, and it only happens when the outside temp is around 90's.
The battery was already about 5 years old and the voltage was not maintaining, the alternator was charging good so I replaced the battery and no codes.
Here we go again, the little Gremlin of codes and this time the codes are:
P0700 - CONFIRMED
U0073 - CONFIRMED
U0100 - CONFIRMED
P0700 - PENDING
U0073 - PENDING
U0101 - PENDING
U0100 - PENDING
U0073 - PERMANENT
U-100 - PERMANENT
This time I checked the charging system with my Fluke meter and found the alternator is charging very low at 12.52v and yet the battery indicator light was just lightly above the voltage threshold level. This only happens when temp is above high 80's the radio is on, the AC is on, the fan blower is set at medium, and the SUV is just coming to a stop.
the Foxwell scan tool voltage was showing 12.20v, the graph was showing from 12.17v to 12.28v
So now what I need to do is to replace the alternator, and confirm the output voltage is at least 13.50v or better

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rednox301

· #2 · 12 mo ago

Normal charging for your vehicle from the GM Repair Manual is 13.8 to 15.5 volts.
This depends on load, temp, battery charge, current sensor on the neg cable, BCM, etc etc.
If you suspect a bad alternator, increase the load by turning on headlights, A/C fan on high, power windows, etc and watch your voltmeter.

A bad alternator is a possibility and probably a good place to start, it could be wiring, BCM, battery current sensor, battery cables, serpentine belt or another thing.

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gnonyx

Discussion Starter · #3 · 12 mo ago

rednox301 said:
Normal charging for your vehicle from the GM Repair Manual is 13.8 to 15.5 volts.
This depends on load, temp, battery charge, current sensor on the neg cable, BCM, etc etc.
If you suspect a bad alternator, increase the load by turning on headlights, A/C fan on high, power windows, etc and watch your voltmeter.

A bad alternator is a possibility and probably a good place to start, it could be wiring, BCM, battery current sensor, battery cables, serpentine belt or another thing.

Thanks for the fast reply, and I did load everything and that's how I got the 12.50 idle voltage.
Is there a fuse link for the alternator or just a fuse box fuse?

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gnonyx

Discussion Starter · #4 · 12 mo ago

Okay, I just checked the charging system with the engine being cold at start up, and the voltage from the battery post is 13.64v, while the alternator post voltage is 14.13v. These reading are from having the AC on, fan on high, headlights on with high beam on, and radio on.
The differences between both readings is just 0.49v
Yesterday outside temp was close to 93* AC on, fan on medium, radio on and the voltage was 12.50.
Would you thing the alternator's insulation is breaking down with high outside temp?
During the winter time I had no issue with any codes or voltage, only when the outside temp is around 90's is when I start to develop these voltage problems.
Any thoughts would be appreciated

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rednox301

· #5 · 12 mo ago

gnonyx said:
Would you thing the alternator's insulation is breaking down with high outside temp?

I would think a bad diode is more likely.
Is there an auto parts store like Auto Zone in your area that can test your alternator?

Fuse number 28, underhood fuse block, is the only fuse for charging other than the big 200 amp one.
This is one of your BCM fuses.

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gnonyx

Discussion Starter · #6 · 12 mo ago

rednox301 said:
I would think a bad diode is more likely.
Is there an auto parts store like Auto Zone in your area that can test your alternator?

Fuse number 28, underhood fuse block, is the only fuse for charging other than the big 200 amp one.
This is one of your BCM fuses.

I'll let you know the outcome when the alternator replacement comes in and install.
Thanks

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gnonyx

Discussion Starter · #7 · 12 mo ago (Edited)

I finally installed the Alternator replacement, and let me tell you something, that is not an easy job, as It took me about 7 hours to do.
After the installation the voltage readings were between 14.5v - 14.75v with AC on fan on low, engine idle
After turning everything on including high beams the voltage was around 13.0v engine on drive not park.
I thing I still have an issue since the Service Stabilitrak come on for a second and disappear.
After doing many research many have different Service Stabilitrak faults from spark plus to wheel hub unit. I'll check the code and se what it claimed to be

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gnonyx

Discussion Starter · #8 · 7 mo ago

Ok Everyone, I finally found my problem of this gremlin I was many issues.
At first it started with Service Stabilitrak, and even if I clean the throttle body and after a couple of months Service Stabilitrak comes back on. I did notice as I give a little of gas the engine would stumble a bit and give more gas it would go away.
I realized the TPS sensor was acting erratic so I got another GM Genuine Parts 12670981 Fuel Injection Throttle Body Assembly with Sensor from Amazon and it was cheaper than Ebay or any other auto shop.

Amazon.com: GM Genuine Parts 12670981 Fuel Injection Throttle Body Assembly with Sensor : Automotive

Buy GM Genuine Parts 12670981 Fuel Injection Throttle Body Assembly with Sensor: Throttle Bodies - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

Now the engine runs great with no more Service Stabilitrak message, as this was some of the tests I was doing.
The engine runs great in the winter but when summer heat comes in is where many codes appears.
Gremlin codes:
P0700 - CONFIRMED
U0073 - CONFIRMED
U0100 - CONFIRMED
P0700 - PENDING
U0073 - PENDING
U0101 - PENDING
U0100 - PENDING
U0073 - PERMANENT
U-100 - PERMANENT
After doing some troubleshooting with the GODIAG GT100+ OBD2 breakout box I found the breakout box between terminal pins 6 & 14 I was getting 67.8 Ω - 68.6 Ω where it should be 60 Ω +or - 1 Ω to 2 Ω.
I purchased a small can of Caig Labs DN5S-2N Deoxit D5 Contact Cleaner and Deoxidizer Mini from Amazon:

Amazon.com: Caig Labs DN5S-2N Deoxit D5 Contact Cleaner and Deoxidizer Mini : Health & Household

Buy Caig Labs DN5S-2N Deoxit D5 Contact Cleaner and Deoxidizer Mini: All-Purpose Cleaners - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

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I disconnect the transmission control module (TCM) electrical connection plug, and spray on both ends of connections with Deoxit D5 Contact Cleaner as well as the ECM electrical connection plugs. Let it dry, reconnected all electrical modules plugs, clear all codes, started engine and drove with no issue.
Finally this past hot summer of having temperature of high 90* the engine ran great with issues, and the ones that was coded permanent eventually got clear after driving the SUV.

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repairman54

· #9 · 7 mo ago

Welcome to the world of diagnostic detective work. Good job !
DeOxit is a standard supply in my ''laboratory''. I use it every time I separate a connector.

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gnonyx

Discussion Starter · #10 · 7 mo ago

Thanks John, and at some point I don't know which relieve my headaches of troubleshooting, the bottle of aspirins or the bottle of wine🤪

I also found this on YouTube for others to better understand how a "Can Bus Networks" operates on modern cars

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