Equinox burning up computers! SOLVED!
I will preface this with a simple statement. Any time I rush through an analysis or skip the root cause analysis testing I normally perform on a module or component failure diagnosis, this happens to me. But, I learn from it every time.
The shop said the customer expressed a concern of the "Service Stabilitrak" light would come on during highway use and the vehicle would die, and would reset after every key cycle. No other warning lights were illuminated after the key cycle.
CONFIRMATION OF CONCERN
I did replicate the concern. Just as the customer stated, a few minutes of highway use would set the drivers information center message, then 8-10 seconds later it would die like you shut the key off, but no amount of in town driving would caused it.
I was called to look at the vehicle and give a diagnosis of the concern, the shop stated that it had a few new parts installed else where and they were told this problem started right after the new components were installed. The customer supplied a receipt for new struts and mounts, EGR valve, plugs, wires, purge valve, PCV, and an alignment.
A full system scan was completed, with a plethora of DTCs among a few modules. Here is a list, don't concern yourself with which modules set them, we will get there.
P0404 egr History
P0442 evap Active
P0455 evap Active
C1779 torque deliver sig Active
B1000 ecu eeprom error Active
U0131 loss comm w/p/s mod History
B1325 dev power 1 circuit Active
C0561 sys disabled serial error Active
RESEARCH TO CREATE A TEST PLAN
So knowing from experience on this platform that a P0404 from an out of date PCM calibration, or from a failed EGR valve will set the C0561, that in turn will turn the "Service Stabiltrak" message on the dash, my bi-directional controls and command vs actual EGR led me to grabing the wiring diagram and starting an inspection of the circuit as no control of the EGR was noted.
ANALYSIS AND TESTING
I quickly noted that the EGR High circuit was shorted to voltage internally in the ECU during my analysis, it was stuck at battery voltage out of the PCM on circuit 1676 (PIN 15 on connector C2 of the PCM) with key on or off.
All powers and grounds were voltage drop load tested good, and a replacement PCM was ordered to be installed and programmed.
That is were I messed up, skipping the route cause analysis has bit me almost every time, this time included.
DIAGNOSIS AND REPAIR
Installed a new(remanufactured AcDelco) ECU, and programmed it, also had to do the steering yaw relearn, rechecked for short to voltage on new ECU, all good, test drove vehicle under conditions and the car gave the same "service stabilitrak" message again, and died again! Rechecked and found short to voltage on high circuit at all times...... AGAIN!!!!
MORAL OF THE STORY
My slip up was I did not test EGR valve. The resistance on the Old(shorted) EGR between low control and high control (EGR pins A & E) was 167.x Ohms, the new valve had a reading of 5.36 kOhms..... BIG difference. Vehicle has new EGR and ECU and has been confirmed good for 1 week! It appears the too low of resistance was burning up the internal circuit in the ECU, and allowing the short to a power somewhere on the board.....
ROOT CAUSE ANALYSIS.......... DO NOT SKIP THIS STEP!
as always I enjoy your write ups and videos. Just curious how did you narrow it down to EGR? Is it because it would only happen at highway speeds?
Nice work Keith! Great write up 👍 its easy to share great learning experiences, but it takes more to share those rough lessons!
Ouch! Thank you for writing … information and your mistake. I think that the second lesson is- Never use Standard Motor Products or Dorman electrical parts, especially in situations where an expensive parts can be damaged if the part is defective! BTW, please never refer to a valve as an "EGR" or a "PCV". It about drives me crazier.
Nice write up Keith, but expensive lesson, and we have all been there on that
".....So knowing from experience that a failed EGR valve, or out of date PCM calibration will set the C0561...." Is that documented anywhere like a PIP or TSB or is this some awesome secret you have unearthed for us?
"This DTC is for information only. As an aid to the technician, this DTC indicates that there are no problems in the ABS/TCS system." This is right from GM's SI. Basically a C0561 states that there is an issue with another module. Also "The electronic brake control module (EBCM) disables the ABS when other electronic control modules set DTCs for components that effect the operation of the
Thanks Andrew, the way he wrote it was misleading to me.
Sorry Geoff, having the P0404 code and the C0561 is a "patern" for this platform, so checking the EGR was my "go to" for this complaint. Ill correct and clarify the post, thanks!
I don't see near enough of any specific model to know any pattern failures, so mentioning the C0561 led me way off course in your article. Basically you had an EGR fault code and were so excited to replace the PCM that you ignored the bad EGR valve, right? :-) I've written-up a few of these type stories in the Tech Tips section of iATN. It helps us remember when we pull a "DOH!!" to not do it
Been there... done that. I feel any of us that say we haven't done similar are sadly mistaken. How often do we forget to go back to basics?
Yes Andrew. The newer and more complex they are, the more we need to know, and the easier it is to forget the very first things we learned. I need to "thank" Chrysler for reminding me, more than once, that a bad valve/seat is just as likely as a bad spark plug. My GM dealer friend sent me some scored camshaft and AFM lifter pictures this morning. He said that is becoming common where he is…
My guys do about 3-4 piston jobs a week, on 1.5, 2.5, 2.4, 5.3 GM motors. The amount of mechanical carnage we see is unbelievable. I do mostly transmission, diesel, and all the in depth diag work so I don't get to do as much of that stuff anymore. I diag it and ship it to the other guys.
Last time I installed a piston was in High School auto shop. Out here in West Maui most customer cars are over 15 years old, and when something on the inside of the engine goes bad, that is the end of it. I do all the diag at the shop here and most cars don't come in until the "google mechanics" have had there hands in it, plus being fourth-owner vehicles we never have any history either. fun
Not quite. Knowing a P0404 will set a C0561 and the "service stabilitrak" message, then following my analysis process sent me to circuit testing, that landed on a bad PCM as my problem. I should have continued with the root cause analysis to complete the testing of the rest of the system, which would have ended with me calling for a PCM and a EGR valve to actually fix the car. Instead I
If your going to keep saying it, you should know it's "root cause analysis". en.wikipedia.org/wiki/Root_caus… Isn't a bad EGR the most obvious/likely/common cause of P0404? I almost never see EGR faults here so I honestly don't know. (I think it's the weather.) I think I've replaced maybe five in my life.
Interesting find. That problem would have eaten my lunch too. Just to clarify, did you measure 167Ω between terminals B & C of the EGR valve on the bench?
I looked at my notes compared to what I wrote, I measured that value between pins A and E, low control and high control, sorry, typed faster than I was thinking.
Excellent! That makes senses now 😊 Nice post. I see C0561 a lot on GM vehicles too. So, you had an ABS code caused by a PCM DTC. The other day, I had a 2006 Buick LaCrosse 3.6L setting a P0318 (Rough Road Sensor Circuit) in the PCM caused by an ABS DTC.
Keith Perkins great write up!! Robby Schrimsher - I just had a low mileage 2006 Impala that came to me after a battery replacement, I have been wanting to write this one up because it was such an odd one. Original BCM was logic locked, I sold them a used BCM. After programming the BCM they had a "service stabilitrak" on the dash and a C0561. They called me up to tell me the used BCM I sold
Hi Michael, It’s recommended that you post a new top level message featuring that intel since you’ll be able to properly tag the vehicle, symptoms, DTC’s, etc in the heading. If you have any questions please let me know.
Keith, I appreciate the write up format. Very nice flow. I don't understand the EGR failure. When I look at the diagram, pins A and E look to be a variable resistor (temperature sensor), not a solenoid. Based on your resistance test I might even guess that is a PTC. I am not connecting the dots for a short and the value of 167 Ohms as being an issue for what looks like a temp sensor or how it
I see the confusion too. That symbol for pins A & E does show a variable resistor, but I think it's just an error. If you look at the connector view for the EGR valve, it also corresponds with the pins descriptions in the PCM. Pins A & E are for the EGR solenoid.
I will say that GM is notorious for having incorrect diagrams, I chased my tail for about 10 minutes on a blower circuit that showed a relay in circuit for what I assumed was a switched ground to the motor, only to find it was not a relay, but a PWM controller for PWM ground, let me tell you I was confused until I read the description of operation. So in the spirit of that, here is a copy and