The subject vehicle is a 2012 Chevrolet Sonic sedan with 1.8L LUW engine and automatic transaxle. However, it is not so much this particular vehicle, but an issue related to a poor wiring termination conditions, that are often encountered in the field and blamed on "XYY" vehicle manufacturer as having "crappy" terminals.
Many times on new vehicles this is due to a supplier manufacturing issue, or at any time thereafter can be induced by technicians when working on other areas of the vehicle in close proximity. Both are apparent in this situation, although the concern was isolated to one circuit at a connector. Sloppy workmanship was evident in the general area.
FWIW, new vehicles may experience terminals that are not properly seated during harness build by suppliers to the vehicle manufacturer. When the line assembly worker connects the harness connector to vehicle components, improperly retained terminals may partially or completely become unseated and immediately back out, or slowly creep out of connection when the vehicle is operated and over the road vibrations result in open circuit conditions.
While technicians do encounter these issues and go on rants about manufacturing, it is relatively hard to catch during vehicle assembly on the line, if the vehicle systems pass the end of line build testing without failing.
Vehicle manufacturers simply assemble systems components from mostly outside suppliers that supply many manufacturers. Often, the suppliers manufacture assemblies adjacent to the vehicle assembly line in real time on demand. Such is lean, just in time manufacturing.
Now, when first approaching a vehicle that is a no-start or has a suspected condition, instead of manipulating harnesses or "prodding and poking" around, it is best to stand back instead of touching anything, lest the condition suddenly be at least temporarily rectified. Encountering a hard failure when previous experiences were unresolved intermittent conditions is an absolute "blessing" if the technician is careful and observant.
The human senses, visual, audible, smell and feel are extremely valuable diagnostic tools when used carefully. Are there any clearly visible clues that might be in an area of concern? Does something sound amiss such as an abnormal cranking cadence? Is there a smell associated with the type of failure ,such as raw fuel or electrical burning smell? Does operating a system result in an unusual feel in combination with any other sensory clues?
There are various conditions that can result in open circuits or high resistance. Poorly crimped terminals, damaged wires, corrosion and hard to see microscopic level oxidation. The latter is associated with the term "terminal fretting" and has become a trendy "buzzword" of late. Here's links to a couple of articles on the condition.
vestest.com/Termina-Fretti….pdf This is a re-post of an August 2009 GM Techlink article
Now, depending if the condition is very mild, cleaning with a contact cleaner and coating with Nyogel 760G (aka ACDelco Connector Grease) or equivalent, may be sufficient to effect a permanent repair. Part numbers vary, depending on country and whether a product is imperial or metric volume, but Nyogel 760G is the product in the container labelled "Connector Grease".
Stabilant 22a is also known to be effective at improving terminal contact and a chemical of choice for many.
However, if fretting has been left long enough to become extensive, replacement of an offending pair of mating terminals may be the only effective long term repair. The best repair is whatever it takes.
Lubricating the terminal must be done carefully so as not to over fill a cavity, resulting in hydraulic lock. The intent is to maintain electrical contact, while allowing for motion due to thermal expansion and vibration etc.
Terminals jammed solidly into two mating connectors will resist any movement and thermal expansion may result in fretting. "Micro" motion with dry terminals can also result in fretting. Sometimes these appear as shiny blemishes, or as bad as arc with metal transferred from one terminal contact surface to the other.
Despite popular belief, gold plated terminals while being more resistant and used for air bag system connections, are not immune from fretting issues, since the plating is extremely thin and microscopic voids in the plating can result.
Technician-induced concerns such as not re-installing or damaged Connector Positive Assurance (CPA) clips, damage to Terminal Positive Assurance (TPA), tanged terminal damage or tang-less terminal locking lance damage, are common issues, as is physical abuse to assist lever design and other difficult to release connectors.
Another pet peeve of mine is wiring harnesses that are miss-routed and not retained securely after other repairs have been completed. Incorrect routing can cause unnecessary strain and open circuits, while wiring that is not secure may contact moving or hot components, or play a part in EMI with another circuit that is now in close proximity. Some technician-induced conditions can be observed in the accompanying photos.
The concern on this vehicle occurred back in 2016 and the since the repair the vehicle has not failed again. At that time, I authored a post on this elsewhere and decided to re-visit the topic here using this particular vehicle, to illustrate how terminal and connector issues are a hot topic that continue plague the trade. Catching one where manipulating a conductor demonstrates the concern isn't always an easy prospect and this vehicle served nicely to illustrate the issue.
It is also not necessarily any more of a concern for any given vehicle manufacturer, but a low volume manufacturer is likely to experience a proportionately lower incidence than a higher volume vehicle manufacturer, leading to an assumption and false belief that the higher vehicle volume manufacturer has more of an issue.
The Customer Concern: This vehicle had been a buy back. It had a history of stalling and had an ECM replaced at 6 km. Applicable recalls had been completed, but the customer was not ultimately satisfied that it was repaired and the vehicle subsequently became a donation to our program when it was a couple of years old.
The car had been in our possession for about a year and never exhibited any issues and the reason for buy back had not been actively pursued, since at the time it was being utilized mostly for basic suspension and brakes training.
One morning while moving the car, the external lighting and instrument panel cluster warning lamps suddenly began flashing erratically. The engine RPM became notably elevated. Power steering operation was completely non-existent one moment and erratic the next. The automatic transaxle shifted hard through the ranges, due to defaulting to high line pressure, as a result of a loss of electronic control.
After an hour or so outside parked outside on the lot and when preparing to move the car into the shop, the engine would not restart and the instrument panel cluster was reacting as here insert no crank video with a no crank condition. Only a distant relay clicking type noise was audible from the driver's seat.
With an assistant instructed to attempt to crank the engine by holding the ignition key in the crank position, it was noted that when wiggling the ECM connector X1 harness where the wiring entered the base of the ECM X1 assist lever connector, it would allow the engine to start and run normally. wiggle test video
Scanning "Vehicle Wide DTCs" resulted in many DTCs as expected might be the case given the symptoms.
Details view of Vehicle Wide DTC check results
The session was saved for later review as necessary. I chose not to evaluate the recorded DTCs at this time, but was mindful of that they might be useful, if I was not able to resolve the concern in a timely manner.
Without having any need to resort to dragging out a PicoScope or other "big guns", GDS 2 with an MDI 1 or 2 would prove to be more than sufficient for the diagnosis. Also incorporated into the mix is the GM Data Bus Diagnostic Tool (DBDT). Connection via the OBD 2 Data Link Connector (DLC) is all that is necessary for these tools.
I am very much an advocate of the "KISS" approach, where the use of minimal tooling as possible should be used to get the job done efficiently. Now, after the fact and for case studies, hauling out the "heavy equipment" to enhance conditions for a case study in class can be beneficial and desirable for best effect.
Given the symptoms, the immediate tool of choice was the DBDT, since I was interested in looking for clues about how the vehicle networks were reacting during the failure. Going the GDS 2 direction would ultimately consume more time than desired at this point. Gut feeling and preliminary checks had already identified an area of concern.
The no crank condition could duplicated at will and the with the DBDT it was noted that the ECM dropped off the list whenever the symptoms and no start occurred. Switching from the "Detected State" view to "Measured Voltage Graphing" clearly showed an issue when the ECM connector X1 manipulated at its base where the wiring harness enters the connector.
I was already aware of this bulletin which did match the conditions: #…E:
Intermittent No Crank/No Start, No Module Communication, MIL, Warning Lights, Vehicle Messages or DTCs Set by Various Control Modules - Diagnosing and Repairing Fretting Corrosion (Disconnect Affected Connector and Apply Dielectric Lubricant) - (Nov 28, 2011).
Now, out in the real world in GM service bays it is handy when published info is applicable and actually results in a repair. However, from experience, "slam dunking" bulletin content and calling it a "fix", is far less commonly successful than might at first believed. Sometimes, despite an absolute match for a condition, the published fix procedure may not result in a verified repair. Never ASSUME.....
Here are some visual clues that identify that some sloppy work has been has taken place in this area of the engine compartment and is supported by a documented ECM replacement at low km, when reviewing "Investigate Vehicle History" files. The oxygen sensor connector harness was also not secured in place.
Removal and inspection of the ECM X1 assist lever connector mechanism to allow inspection of the wires, terminals and connections to the ECM, revealed some damage to the CPA that secures the assist lever in the latched position.
The CPA stops the lever from moving, while the lever latches and locks the harness connector body securely to the ECM connector. Insert CPA
The harness in this area was also not secured. After removal the latching and locking "paraphernalia", the condition was still present while wiggling the harness where it entered the connector body. Manipulating individual wires identified only one wire that was associated with the fault.
Fretting is a known condition, where oxidation of terminal connections due to abrasion from thermal cycling, vibration etc, can lead to a loss of connection. Cycling a connector with terminals that exhibit symptoms of fretting often tends to result in a temporary fix, as became the situation on this car.
Closer inspection of the ECM pins under magnification did not reveal any obvious terminal fretting, but then we are dealing with corrosion at microscopic levels in some cases. My preference is to use a new mating terminal to test pin drag and tension, rather than a "used and abused" service probe, which do wear and can become deformed during frequent use.
Feeling the two mating terminals as they slide together and apart can often identify a terminal with fretting issues, since the surface may be rough enough to feel the condition. This takes a little care and attention to detail.
However, terminal tension and drag testing results did not identify any abnormal condition. There were no loose terminals and since no single wire seemed to affect the condition any more, since cycling the connector a few times appeared to have restored normal operation.
I suspected that a "fretting" condition existed, possibly exacerbated by the non-secured harness that was affected by movement in the engine compartment. During normal operation, terminals expand and contract slightly and move relative to one another.
If too tight or jammed together, friction between the terminal male and female terminal contact causes abrasion of the surface, which results in microscopic pitting and eventually oxidation, if left unchecked in the harsh environment that automotive connections must survive.
A light terminal cleaning and application of Connector Grease, securing the harness and oxygen sensor connector, in addition to replacement of the harness to connector cable tie, connector cover, latching lever and the CPA.
This repair was completed in 2016 and the concern has not since recurred.
Hi Marty: I'm familiar with that document. Funny thing about that and your comment about Stabilant 22. Some years ago, I had a conversation (argument?, meaning logical discussion of thought) with Rags and some of the other heavy hitters (thinking people) over whether it is better to use a dielectric or Stabilant. I was in the Stabilant camp, alone. All of the others were in the dielectric…
Hi Guido. I fully agree with your perspective as I wondered about it too. I recall the debate and miss some of those times. Here's some links to some light reading. nyelubricants.com/stuff/contentm….pdf w8ji.com/images/Cars/Ba….pdf w8ji.com/dielectric_gre… This quote from the last link makes the most sense. "One…
Hi Marty: I looked at the product sheet but hadn't seen the Nye link that you posted. It was very educational. The part which jumped out at me is the resistance standard for connectors, .010 ohms. I hope that number is registering with people. Ten milliohms allowable resistance across a connector terminal after repeated matings - I think that calls for a Scotch-Lok or two. Thanks, Guido
Hi Martin, Thank you for sharing. It is good to know that there is something other than dielectric grease available. I think I will purchase some Stabilant 22. When diagnosing behind others I find many connectors with a "liberal" amount of dielectric grease applied. Sometimes I wonder how they got the connectors to mate with a tube of dielectric dumped in. A little is OK. A lot seems like it…
Hi Mike. I always got a kick out of brake issues, where cleaning and lubricating was a fix, that could easily have been avoided if it had been applied during vehicle assembly.
Thanks Mike. I used Stabilant 22A many years ago, probably in the mid '80s in the dealership and it worked just fine. Then came along Nyogel 760G and it works fine for me too. You are correct, packing connectors with too much grease can cause issues. GM Bulletin …C doc # 2741490 addresses various electrical issues and advises against excessive use of connector grease (connector in…