2018 GMC Acadia 3.6L P219A code help needed (O2 sensor waveforms posted)

Hello all, 

2018 GMC Acadia 3.6L V6 62,000 miles bought used.  Not long after purchase the check engine light illuminated and I see a P219A which I understand to be a fuel mixture problem on the bank 1 cylinders.  The check engine light will illuminate, and then go out a few drive cycles later but the code is still stored.  I have copied PID freeze frame below.  Car runs and drives great, no noticeable problems with the engine.  Transmission shifts sort of weird but that's a separate issue I am investigating.  

Things I have done:

-Monitor live 02 readings.  Bank 1 upstream is a sort of dirty wave form compared with bank 2 which shows a nice quasi sine wave.  Not sure if that's a problem.   Bank 1 and 2 downstream seem to keep a fairly constant .745ish at idle.   
-I checked electrical connections and can not find anything out of place or burned, loose, corroded. 
-I checked the Bank 1 upstream heater element and it reads 6.3 ohms so that's fine I guess. 
-I removed the air filter and vacuumed out the dirty side of box.  Element was a bit dirty but nothing crazy.  
-I checked the oil and I do not detect an overt fuel smell, smells like oil when I do an oil change.  I know bad injector can be a cause of P219A. 

I am hoping to fix this myself if possible.  Thanks all.  

Freeze frame data: 

FUELSTS1 CL
FUELSYS2 CL
LOAD_PCR % 44.7
ECT (F) 194
SHRTFT1 % -.8
LONGFT1 % -14.8
SHRTFT2 % -.8
LONGFT2 % -11.7
FRP psi 53.5
MAP psi 10.3
RPM 1965
VSS mph 70
SPARKADV degrees 35.5
IAT (F) 109
MAF lb/s .06
TP % 32.2
02B1S1 Voltage .190
SHRTFTB1S1 % -.8
02B1S2 voltage .730
SHRTFTB1S2 N/A
02B2S1 voltage .430
SHRTFTB2S1 % .8
O2B2S2 voltage .670
SHRTFTB2S2 % 99.2
RUNTM sec 417
FRP psi 900.6
EVAP_PCT % 95.3
FLI % 82.7
WARM_UPS 3
CLR_DIST miles 101
EVAP_VP inH2o -3.398
BARO psi 14.4
CATEMP11(f) 1563
CATEMP21 (f) 1563
VPWR voltage 14.068
LOAD_ABS % 36.1
EQ_RAT .999
TP_R % 22
AAT (F) 104
TP_B % 32.2
APP_D % 31.8
APP_E % 15.3
TAC_PCT % 29.8
IAT II (F) 109


 

Here's some info on the code meaning. Starts at 36 minutes, 46 seconds.

Thank you for this. That is very interesting.  So the PCM can infer the exact cylinder that is having issues based on timing the pulse etc, that's neat.  Since mine is only showing a P219A without a follow up code for an individual cylinder I am not sure what to make of it.  The upstream O2 sensor for that bank does indeed show a noisier signal.  I dont know what the bandwidth of these hand held scanners is, but for sure it looks noisier than the other side.  I do have a 70mhz oscilloscope here but not sure how to hook it up in an automotive application...or if it would provide more meaningful information on this 02 sensor. 

So, if I only have a P219A code without an individual cylinder fault, might this point to a faulty upstream o2 sensor?  I figured the dirty 02 sensor signal could be either from a fault with the ignition/fuel delivery or the sensor.  Is there a way to rule out the sensor short of replacing it?   Perhaps GM does not use those other P219 codes for individual cylinders?   

Oh, also the LT fuel trims are fairly consistent -10 to -14%.  Not sure if this could be related.  I thought maybe a leaky injector but no overt fuel smell from the oil.  Fuel economy seems acceptable, 28 hwy 21-22 mixed city/hwy.  

Scan data is fairly low bandwith. Not near fast enough to identify something which may be cylinder specific.

You could try 'scoping the O2 signal along with an ignition sync. That might show whether you have a repeating O2 oscillation tied to the firing order.

Ill give that a shot, ordered the back probes for my scope.  Where do I tie in so I can trigger to the ignition sync? 

Looks like that thing has 4 wire coils. Comparing two adjacent coils they should have two wires with matching colors. That'll be your powers and grounds.The other two wires are the control and feedback wires. You ideally want the control wire but the feedback one would probably work too.

P219A/P219B or P1171/P1174 are real fun codes to diagnose. :silly:

For whatever it's worth, every time I've run into this code, it's been an injector problem. You can have an injector that causes somewhat incomplete combustion, but isn't enough to flag the misfire monitor or skew fuel trims.

My usual procedure is to treat it like a misfire code, and check for anything that can cause a contribution problem. Ignition, intake, exhaust, mechanical integrity. If that all checks out, injector time.

I really appreciate the input from everyone.  We purchased this car recently and my wife has been a bit upset about the CEL coming on so soon...but used car.  

Man I hope its not an injector, but it is what it is.   I think GM advises NOT to run injector cleaner through these vehicles otherwise I would try that.  

I will try scoping the o2 sensor and triggering to the ignition and see if I can detect a rhythmic anomaly of some sort.    Any recommendations on other checks a home tinkerer could do on those other areas before taking it to a shop? 

Sorry for the noobish question, but is there usually an accessible ground reference for probing sensor outputs?   My understanding is there is a chassis ground and a dedicated sensor grounding system with these computer controlled cars.  

Hello everyone, 

The check engine light will go off and then come back on again after a couple hundred miles, where it displays the P219A code again as an active code.  Does this indicate an intermittent fault?  When I checked after the check engine light returned it still displayed the same freeze frame data from before the light went off, I assumed I would have a fresh freeze frame from from this latest occurrence.  Is this a limitation of my scanner?  

 

Hello everyone, 

Sorry for the rambling below, trying to do a few things at once please bear with me..

I have some more observations that I hope will point in a certain direction.  I am fairly sure my issue is not with an 02 sensor but I think I will swap them side to side and see if the code follows the sensor.  

Our climate here is currently high 103-110F, and I have observed the fuel trims at -12 to -18 on both banks at idle, and when driving sometimes will spike to -25.  No fuel trim codes.  While on vacation this last week I added a bottle of techron since my P219A could be related to a dirty or damaged fuel injector, this at a location with a cooler climate (high 65-70F). The adding of techron and traveling to a cooler climate happened at the same time.  Immediately the fuel trims seemed to stabilize around -7.8 ish on both banks at idle and under load I did not see and crazy spikes up past -25.   We have since returned to the warmer climate and the fuel trims have returned to -12 to -18.    Might this point to a defective MAF sensor?  I have observed the sensor changing its readings during operation so I had assumed it was fine.  I am assuming negative trims and my P219A are related in some way which is why I am focusing on it.  

Ill stress once more there are absolutely no concerns with how the engine runs.  Lots of power when needed, smooth, starts perfectly.  I wouldnt know something is wrong except for the CEL and the P219A code. 

Since I have the probes now I decided to capture the waveforms on both upstream O2 sensors on my DSO.   I probed the signal and ground directly from the connector.  I am really interested in your thoughts on these, they are quite different form bank to bank.  I am going to swap them side to side this afternoon.   

Bank 1 idle:
 

Bank 2 idle:


Bank 1 2000RPM:


Bank 2 2000RPM:

I swapped o2 upstream o2 sensors side to side and the problem (dirty wave forms as above) did not follow the o2 sensor.  I figured this would be the case.  I also removed the evap line from the purge valve and found that it is not stuck open. 

Other relevant information (I think):

1- Long term fuel trims are biased negative so that rules out a vacuum leak right? 
2- I do not perceive an exhaust leak, no ticking or puffing that I can see/hear. Could a super tiny exhaust leak cause this problem?  Its sort of difficult to thoroughly examine the bank 1 side since its against the firewall. 
3- I get no misfire codes or anything related to the coils or spark plugs.  
4- Maybe relevant, the fuel economy estimate on the Acadia is about 1-2MPG high. 
5- Again, it runs and drives perfectly fine.  

I am going to clean the MAF sensor (thinking of the negative biased LTFT on both sides) but I do not have confidence that this will have much effect.  I think I will also remove and inspect the spark plugs and coils on that side if the MAF cleaning does not bear fruit.  

I want to rule out everything before I dive into replacing the injectors.  What have I missed?  Are there any other diagnostics I can do that would help pinpoint this?  

 

Before swapping the front O2 sensors the bank 2 sensor showed slower response time. I suppose he did the same when placed into bank 1?

Do you have a chance to borescope the intake/cylinder for carbon built up at this milage?

I have not scoped the sensors since changing them but I can. 

I do have a bore scope, can this be fed through the throttle body or is there a better way to look at the intake ports? 

You may introduce the borescope thru the spark plugs hole, and youll be able to see the pistons as well as parts of the (opened) valves, depending on the flexibility of your scope.

Thru the throttle body it's difficult to get to the intake ports, maybe some vacuum hoses will provide easier access.

Excellent, thank you I will do that when I inspect the coils and spark plugs. 

Also I noticed this car has two PIDs for fuel pressure, one around 57-60psi and one much higher above 500psi.  When I shut the engine off I continue to get data on my scanner for 20-30 seconds and it shows psi increasing slowly on both PIDs.  This would rule out a leaking injector no?  

Yes, the rising fuel pressure on the high side after a hot soak indicates no injector leak down.

Was this issue ever resolved? If so, what diagnostics procedures did you use to come to the correct conclusion and what was said conclusion? I am dealing with a similar issue on an identical vehicle.

Scoping the o2 sensor signals and seeing the dirty signal on the side with the code was as far as I got with it. We ended up taking it to the dealer and they changed the injectors on that side, problem solved.