2016 Chevy Cruze Limited "Service Charging System" P0621 Case Study

First things first, I want to apologize if this technically isn't a case study, but I want to run down my diagnostic list that I have done with this particular vehicle.

So... Prior to this vehicle coming in again...yes, again...It was here last week being worked on by our shop foreman for the cam cover leaking. Shop foreman ended up doing parts warranty on the cam cover due to leaks on the front part of the cover. He also found two bolt holes stripped in the head which resulted in drilling, tapping, and inserting a helicoil into the head with silicone being put on the entire sealing portion of the head. (Just want to point out, this isn't my place to comment on his work and my word personally won't stand at this dealership). The problem with this is he either ended up drilling too far or something to the point that when the crankcase had pressure on it, it would blow oil out of the places where the bolt holes were drilled, thus resulting in an oil bath being showered upon the entire front end of the engine and engine bay. Again, silicone was used fix the leaks and I was told that after using 6 cans of brake clean to clean the engine and bay, an addition water bath was given before being sent back out to the customer.

Here's where I get the car. Customer comes back for a "Service Charging System" message displayed in DIC and Battery MIL illuminated. Verified this both driving the car into the shop and on a test drive. P0621 shows up current on GDS2, battery voltage is at 11.6v according to the scan tool voltage and DIC. The kicker now becomes this. Whilst in the shop, prior to another test drive, I found that excitation does happen, but this seems to be either switching or is an intermittent issue. The reason I say this is because the alternator would begin charging (and so we're clear, this is a 2-pin L-F alternator) the battery at approximately 14.5v-15.1v. As I test drove the vehicle, after approximately 2 miles of driving, the alternator decided to quit charging and I watched the voltage steadily drop back down to 11.6v as I came back to the dealership after a roughly 5-7 mile drive.

Honestly, this should be a cut and dry case. Given the history on this car and what's currently happening to it, there should be no doubt that this is an alternator, but me not wanting to be a parts changer, I follow GM Service Information (SI) for diagnostic procedure.

VERIFICATION

Now, obviously, GM wants you to verify the code. If it is current or set as current, you proceed to system circuit testing.

SYSTEM CIRCUIT TESTING

For this section, I'm actually going to copy/paste word-for-word what the diagnostic testing procedure says and my path. I will bold and underline what my results were.

1. Verify a test lamp illuminates between the G13 Generator B+ circuit terminal A X1, B X1 or 1 X1, and ground. ILLUMINATED, tested at 12v stud behind alternator and alternator case ground
*If the test lamp illuminates
2. Disconnect the X2 harness connector at the G13 Generator, ignition ON.
3. Test for 1 V or greater between the control circuit terminal 1 X2 and ground. This is obviously the L terminal on the alternator or connector. SI wants you to test on connector, not alternator.
If less than 1 V Using Fluke 17B+, My reading was 0.751v
Ignition OFF, disconnect the harness connectors at the K20 Engine Control Module.
Test for infinite resistance between the control circuit and ground.
If less than infinite resistance, repair the short to ground on the circuit.
If infinite resistance This is where I got a little confused. I originally plugged the connector back into the alternator and noticed it had 386 Ohms. Realizing the diagnostic instructions did not call for the connector to be plugged back in, I removed the connector from the alternator, thus getting an O.L reading on the DMM, meaning that there isn't a short to voltage/ground issue or any need to check contact points.
Test for less than 2 Ω in the control circuit end to end. This tested at 0.1ohms.
If greater than 2 Ω, repair the open/high resistance in the circuit.
If less than 2 Ω, replace the K20 Engine Control Module.

Now, I don't know about you, but I had to check over myself multiple times because I didn't want to believe I was having to condemn the ECM considering this vehicles state and history. Forgive me, but I do want to point out that I did end up cleaning more oil residue off the engine and alternator using brake clean and compressed air in order to test if the alternator was actually bad and visual inspections of the electrical system yielded good results as connector ends and such were clean and in good condition, no terminal fretting that I could tell at ECM (just dealt with this on a 2021 Colorado with 58 miles on ODO.). So, I gave the news to my manager and told her that I didn't think this was fully the right call to make as I didn't have any other diagnostics to run with. Currently, the customers are as confused as we are and they will be back Monday for either alternator or ECM.

I honestly want some feedback on this and request some sort of additional tests I can do to verify for a fact that I can either condemn the alternator or ECM. Thanks in advance!

No apologies needed! You're welcome to post problem vehicles like this whenever you like.

What's the 8th VIN digit? Or the engine RPO, either way. Mostly trying to follow along with SI. I took a guess at an LE2. :silly:

Not that I'm trying to sweat you, but I am curious to know what the Gen L PID was doing on your test drive, specifically what it was doing when the alternator stopped charging. If you can make it fail in the bay, so much the better!

The System Verification has an unplug-it test that I've used in the past for concerns like this. The Gen L PID isn't quite as good as watching the voltage directly, IMO, but still valuable. The Circuit Verification test is definitely... vague. I don't know that I could call a PCM based on that result, either. Based on what you've said so far, I'd go alternator.

Just curious, did you happen to notice any fluids in the PCM connectors when you were testing? I've seen several Cruzes with water intrusion in the PCM connectors, causing all kinds of wackyness. Flickering warning lights, intermittent codes, like that.

Tyler wrote: No apologies needed! You're welcome to post problem vehicles like this whenever you like.

What's the 8th VIN digit? Or the engine RPO, either way. Mostly trying to follow along with SI. I took a guess at an LE2. :silly:

Not that I'm trying to sweat you, but I am curious to know what the Gen L PID was doing on your test drive, specifically what it was doing when the alternator stopped charging. If you can make it fail in the bay, so much the better!

The System Verification has an unplug-it test that I've used in the past for concerns like this. The Gen L PID isn't quite as good as watching the voltage directly, IMO, but still valuable. The Circuit Verification test is definitely... vague. I don't know that I could call a PCM based on that result, either. Based on what you've said so far, I'd go alternator.

Just curious, did you happen to notice any fluids in the PCM connectors when you were testing? I've seen several Cruzes with water intrusion in the PCM connectors, causing all kinds of wackyness. Flickering warning lights, intermittent codes, like that.

Engine RPO is LUV. The ever so lovely 1.4L Turbo.

Trust me, I sweat constantly, but mainly cause I've become a bigger guy. Lol. And I'll be honest, I have no idea in that regard. So, there's no concrete evidence there and I had that thought sitting in my head when I test drove it, and the worst part is I could've used the laptop to find out, but ran off limited info and a little bit of frustration. So, I'll take that bit as a minor oopsie on my part for not obtaining that data.

With the X2 connector on the PCM, I did not see any signs of wicking and didn't see any signs of oil or fluid on the PCM at time of testing and diagnosing.

I mean, every which way you look at this, it is a textbook alternator situation. Being that I'm a younger tech with not much diag experience and a shop foreman that really won't tell you diddly, calling it as an alternator can be difficult and the only reason I really practice the diagnostics for it is simply for warranty for the time being, but also because I want to bring my comebacks down, not that I have a lot anyway. Just want to be good at it.

Just unplug it front probe l terminal start car up see if ya got 5 volts or close to it

Have any bi directional controls to turn alternator on and off?

Cheryl wrote: Have any bi directional controls to turn alternator on and off?

I was able to look this morning. L terminal command PID. Shows ON. command duty cycle was in the 80% range. Decided to take manual control with the engine on and tested X2 terminal 1 again and it showed 4.52v. It's an alternator.

I was able to look this morning. L terminal command PID. Shows ON. command duty cycle was in the 80% range. Decided to take manual control with the engine on and tested X2 terminal 1 again and it showed 4.52v. It's an alternator.

I like it. Alternator that SOB and SEND IT.

Not trying to introduce doubt, but I do see my fair share of LUV engines in the aftermarket. Can't say I've seen an alternator problem on any of them. :silly: I'm really not doubting your call - I'm trying to decide how much the previous repairs factored in to the alternator failure.