We all have pet hates or put differently, we all have things we'd rather not do if we had a choice. For instance, some of us have an intense dislike of finding and fixing rattles and squeaks. Some of us would rather not find and fix CAN bus issues, while most of us would rather not find and fix water leaks around windscreens and sunroofs, but we are sure you have your own personal favourites.
We can list many other examples of pet hates here, such as this writer’s favourite- diagnosing problems that don’t have unambiguous symptoms like stored trouble codes, flashing warning lights, clearly discernible drivability issues, knocking and rattling engines, impending engine or transmission failure, and the like. Such symptoms and signs usually point one in the right diagnostic direction, but given our collective experience is that it is much easier to fix issues you can see, hear, feel, or smell than it is to fix issues that do not produce unambiguous symptoms, how does one resolve a problem that produces no discernible symptoms at all?
The above question is neither idle nor rhetorical because this writer was recently engaged by the owner of a symptom-less 2001 Honda Accord with a 2.3L engine to find out why none of the OBD II system’s readiness monitors had run for nearly two years.
You might think that it is unlikely or even improbable that all of an OBD II-compliant vehicle’s readiness monitors can fail to initiate without producing symptoms or evidence of such failures over an extended period, and this writer did think so too. Thus, in this two-part article, we will discuss this case in some detail, but most importantly, we will explain how we solved the problem by using a piece of obsolete software that required an equally obsolete computer to run. Before we get to specifics, though, let us state-
We need not spend too much time on how this writer got involved with the problem vehicle beyond saying that its new owner had inherited the vehicle from a deceased relative, who happened to be a former employee of this writer.
Briefly, the Honda's history was as follows: its previous owner bought it from a Honda dealership as a used vehicle, and although they had put more than 350,000 km on it in the time they owned it, the vehicle was well maintained and in an excellent condition for its age and mileage. Also, the previous owner kept meticulous records of all maintenance and repair work ever done on the vehicle, so when the current owner perused the vehicle's service history, he noticed that it had undergone several full diagnostic scans, all of which gave the vehicle a clean bill of health. All diagnostic reports showed that no faults were found.
During this discussion, it turned out that the Honda's new owner was a senior apprentice at a company providing specialist diagnostic services on heavy aircraft, so it seemed improbable to him that a car with nearly 400,000 km on the clock as a daily driver could be without faults -even minor ones. As the young man said at the time, it was not about there being no faults on the vehicle; it was about the improbability of there being no faults present on the vehicle. He rationalized this by adding that even brand-new heavy aircraft always have many faults, so he could not accept that his newly acquired Honda had no faults.
To prove this hypothesis, the young man started taking the Honda to a series of dealerships to have the vehicle scanned, but all diagnostic reports stated that there were no faults on the vehicle. The whole thing came across as a bizarre and misguided attempt to prove modern automotive diagnostic equipment somehow wrong or incompetent, but not to be deterred, the young man started buying a series of Honda-specific diagnostic software suites and a few high-end scan tools that could run the software to performs his own scans. Needless to say, he came up empty every time.
By this time, the story had become tedious and somewhat ridiculous until the young man mentioned that he had obtained the latest iteration of the software law enforcement and environmental protection agencies in the USA use to perform mandatory emissions testing in jurisdictions that require such testing. This writer thought it best not to ask how he had come by this software, but in case you are not aware, this software does not test OBD II-compliant vehicles for the presence of faults. The primary function of this software is to-
- and most importantly, to check and confirm that all readiness monitors can, and will initiate and run to completion when they should, since readiness monitors act as the “eyes and ears” of the OBD II systems’ overall emissions control functions. As expected by the Honda's owner, this diagnostic test report showed that no readiness monitors had been initiated for nearly two years, even though the vehicle had been in daily use until a week or so before its previous owner’s passing
We can skip over the details of the discussion that followed this revelation, but suffice it to say that despite his better judgment, this writer agreed to "take a look" and let the vehicle's owner know what he finds, but before we get to what he did find, let us look at-
As we all know, all diagnostic procedures must start with replicating the problem, so this writer scanned the vehicle with the latest iteration of Honda’s diagnostic software using all available modes, thinking that it might pick up issues that generic software could not but this scan turned up no active, pending, or historical codes in any control modules. In short, the Honda’s electronics performed like it had just left the factory.
Next, and acting on a hunch, this writer connected a digital storage oscilloscope to the DLC and scoped the operation of the CAN bus system during a 50 km or so test drive. The vehicle performed flawlessly during the test drive: no warning lights came on, the engine was as smooth as silk, and all gearshifts were smooth and predictable. The only thing that was slightly out of place was that the idling speed consistently hovered around 1000 RPM, which was about 200 RPM too high, but at the time, this writer did not think this was a major issue. It turned out later that he was wrong about this, but we will get to that in Part 2 of this article.
Moreover, reviewing the live CAN bus data showed that the positive and negative circuits mirrored each other perfectly during the entire trip as the CAN bus system transmitted data back and forth between control modules. There were also no anomalies, glitches, signal dropouts, or resonance between the CAN circuits at any point during the test drive.
This was all very strange since it was not possible for readiness monitor failures not to leave traces of such failures where manufacturer-specific diagnostic software cannot access such traces, so this problem needed some deep and careful thinking about.
Given that there was no reason to believe that the specialised emissions testing software was somehow defective or deficient in some way, the problem likely involved the implementation of one or more OBD II protocols on this Honda model. This was a tempting thought, but it seemed somewhat more likely that the specialized emissions testing software could access fault setting parameters or PIDs that purely diagnostic software cannot access or don't need to access, to extract fault codes. At the time, this seemed like a reasonable assumption to make given that emissions testing software tests the functionality of OBD II systems, as opposed to interrogating control modules for the presence of fault codes.
There matters stood for a few days while this writer attended to other business while, at the same time, letting the problem “stew” in his subconscious mind. This strategy often produces genius-level insights into tricky problems when one is not actively thinking about said tricky problems, and so after a few days, this writer began to think that the solution to this problem might involve the early history of OBD II systems, which leaves us with just-
As it turned out, this was indeed a genius-level insight, and in Part 2 of this article, we will discuss some of the details of how this insight helped to restore the proper functioning of the Honda’s readiness monitors.
