What do you do when you are confronted with an obscure fault code, or with multiple fault codes that don’t appear to be related? Do you simply clear the codes, take the vehicle for a test drive, and see which codes return? We have all done this, but if truth were told, this is not the most efficient way to go about diagnosing faults since some codes may not return immediately, which effectively, makes our customers unwilling partners in our diagnostic and fault repair validation processes when a code reappears two days later. To help you avoid such embarrassing situations, this article will discuss a better way to approach diagnostics by using PID’s, but more specifically, how fault code setting parameters can be used as diagnostic aids, starting with this question-
All experienced technicians know and understand that fault codes are set when something goes wrong on a vehicle, and that “wrong” is defined by a set of rules or enabling conditions that must be met before a code (depending on the applicable detection logic) first enters a pending state, before becoming an active code when the fault persists.
However, if you are new to automotive diagnostics you may not yet realise just how wide the proverbial net that represents a set of rules or enabling conditions really is. In the case of generic codes, the setting parameters are usually published in technical information sources, but in general, generic code setting parameters include the following-
Required conditions
These are conditions that must be met before a code can be set-
Code and/or monitor interactions
This refers to the effect(s) the setting of one or more codes may have on other, but usually related systems and/or codes.
Data ranges
This information includes the upper and lower limits of voltages, currents, and/or resistance values. Any electrical value that falls outside of these ranges will typically cause one or more codes to set.
Monitors
This information will typically include the frequency of the self-diagnostic test or monitor that detected a fault, such whether the test or monitor is continuous, or once-per-trip. Other information could include the-
It should be noted though that while the above list of code setting parameters is neither complete, nor exhaustive, it should suffice to illustrate the point that when taken together, code-setting parameters are arguably more valuable as diagnostic aids than symptoms are by themselves since generic code setting parameters are known, and can therefore be used to define a failure or malfunction to a high degree of certainty.
In fact, all vehicle manufacturers who either produce or sell vehicles in the USA are compelled by legislation to make almost all generic code-setting parameters available to both the independent repair trade, as well as to the public, which means that this information is freely available to anybody who wants or needs it via the internet.
However, the situation is somewhat different with many, if not most manufacturer specific codes. In these cases, vehicle manufacturers are free to develop their own proprietary PID’s, and they are not obliged to share this information with anybody, including manufacturers of diagnostic equipment that is available to the independent repair trade.
Despite this state of affairs though, it is still possible to use code setting-parameters, as opposed to symptoms, to diagnose many manufacturer specific (and some generic) issues, although the process of obtaining or figuring out the parameters that were exceeded to set the code is sometimes less than easy. This is especially true in cases where although there may be no driveability issues present that could offer clues as to the possible root cause(s) the issue, one or more codes have announced themselves via one or more illuminated warning lights on the dashboard. Let us look at a typical example of such a situation-
While code P0A80 is a generic code that applies to all hybrid vehicles, Toyota has been notoriously reluctant to release some of the parameters that apply to the hybrid battery packs of their Prius model range. Note that herein lays an object lesson for many technicians, since not all instances of code P0A80 require replacement of the hugely expensive battery pack, so let us look at code P0A80 in a little more detail-
If you are not familiar with code P0A80 on Toyota Prius models, you may be interested to know that the most common symptoms of this code include an illuminated MIL light, increased fuel consumption, and the fact that the petrol engine runs for longer periods than it used to do. Moreover, these symptoms are often the result of V-block inefficiencies, a V-block being a pair of battery modules* that is monitored with a continuous monitor; in practice, a Prius hybrid battery pack consists of 28 battery modules that are monitored in 14 V-block pairs.
* On for instance, Prius models from 2004 to 2009, each module is made up of six Nickel-Metal Hydride cells, each of which has a nominal voltage of 1.2V, which translates into an average voltage of 7.2V for each module. Since the 28 modules are connected in series, the battery packs’ total voltage is 201.6V and most hybrid battery packs can deliver more than 150 Amps.
So if you scan a Prius with a high-end scan tool, the only PID information you are likely to get is that one V-block is exhibiting a voltage deviation of a certain percentage relative to the others, and that according to Toyota’s “DTC Detection Condition”, the code uses two-trip detection logic. The only other information you may receive is that the deviation in the efficiency of the defective V-block has exceeded a specified threshold.
There is not much to go on here, which is made worse by the facts that the voltage level of the defective V-block is listed as having exceeded (or fell below) a “Typical Malfunction Threshold”, and that the threshold is defined a “Standard [Deviation] Level”. Additionally, the acceptable operating voltage range of V-blocks are listed as being “Toyota Intellectual Property”, and there will be no information of what constitutes the enabling conditions for this code, or of what constitutes a drive cycle, which means that replicating the conditions that had set the code now becomes a matter of guesswork.
So how would you approach this problem if you have neither freeze frame data, nor access to Toyota’s Techstream diagnostic software? You could of course refer the vehicle to a Toyota dealer, but there is a way to diagnose the issue using the available scan tool data, the fact that only one V-block is affected, and your existing knowledge of hybrid battery packs. However, to do this, you need to-
The first thing you need to do is make sure that you are not dealing with a ghost code, which means that you have to replicate the code under the type of conditions that were most likely to have produced the P0A80 code. Since you know that, a) the code uses two-trip detection logic, and b) that hybrid battery codes don’t disappear by themselves, you can clear the code and then attempt to replicate the conditions that caused to code to set the first time.
The voltages of hybrid battery modules or blocks can vary from one block to the next depending on load, state of charge of the whole battery pack, and the age of the battery. However, since you know that the issue involves a voltage fluctuation or deviation when the battery is under load, performing load tests on each individual block (or cell) is highly unlikely to produce consistent or even useable results. Thus, the only reliable way to load the hybrid battery pack consistently is to perform several hard accelerations, followed by equally hard braking events to cause the voltage in each block or cell to spike. Note though that the vehicle has to be shut down completely after each test to simulate drive cycles accurately.
If you do this with a scan tool connected and set to monitor battery block PID’s, it is likely that the code will reset at the start of the third test, and with some luck, the same V-block will show up as being defective. If it does, you have successfully replicated the fault, so now you know under what conditions the code set the first time- high loads on the battery.
Nonetheless, now that you know you are not dealing with a ghost code, you really need to take a step back to avoid getting tunnel vision on the one hand, and to avoid electrocuting yourself with a car battery, on the other. At this point, you need to do two things- obtain as much information about the customers’ concern as you can, and research the problem as deeply as you can.
This does not only apply to hybrid battery issues- it applies to all trouble codes for which you do not have sufficient PID information to make a definitive diagnosis, but in the case of our example Prius battery pack, you could ask the customer the following questions to get a better sense of the problem-
When did the issue first appear?
While knowing the duration of the issue is important, it is also important to know if the problem has been getting worse lately, and if so, how much worse it has become.
Did the vehicles’ performance change in any way?
Apart from the decrease in fuel economy, has the vehicle become noticeably sluggish, and if so, is it only under heavy loads, or has it become sluggish over range of driving conditions?
What other work has recently been done on the vehicle?
Here it is important to focus on work/repairs that may have been done to the vehicle’s electrical system, and particularly to the hybrid propulsion system. If possible, ask the customer to provide invoices for recent work, so that you can see first-hand what was done to the vehicle, and how that might be related to the current issue.
Had the hybrid battery pack been deeply discharged recently?
This is particularly important, since the polarity of one or more cells in some types of hybrid battery packs can be irreparably damaged or even reverse their polarity when they are deeply discharged. Bear in mind that hybrid battery packs are not deep-cycle batteries; they only last for as long as they do because they use at most 40% or so of their rated capacity at any given moment.
Apart from the above, you should also perform a thorough visual inspection of the vehicle to check for obvious signs of accident damage, the presence of water leaks into the vehicle, or signs of tampering with any parts or components that could conceivably have caused or contributed to the current issue, before continuing to-
This also applies to all codes for which you have insufficient PID information, but in the case under discussion, you can add what PID information you have to what you know about batteries in general.
In this case, you know that-
You also know that all V-blocks are connected in series, which is a potentially valuable piece of information since one battery (in this case, a V-block or module) that is connected in series with others does not necessarily have to be defective to deviate from all or any other V-blocks or modules in the series.
So if you are comfortable with the idea of working on a battery that could electrocute you, you can now disable the battery by removing the service plug, and begin to check the voltage and state of charge of each individual cell or module in the battery pack. Bear in mind that it is highly likely that you will find marginally different test results for each cell or module, but having said that, the cell or module with the biggest deviation will be the defective one.
NOTE: While this article is not intended to be a hybrid battery pack repair guide, it is worth noting that corrosion of the bus bars on battery packs is arguably the single biggest cause of code P0A80 and others that relate to state of charge or charging imbalances. Thus, removing the bus bars and cleaning off corrosion with a strong water and vinegar solution will often resolve a variety of battery pack codes on hybrid vehicles.
Although this article focused heavily on hybrid battery packs, the principles that are described herein also apply to all other codes and issues that do not have the benefit of complete or comprehensive PID information or freeze frame data.
In fact, there is always at least one piece of information available, even if is just details on the detection logic used for a manufacturer specific code. This means that if you have a sound theoretical knowledge of the system a particular code relates to, you can use your analytical and critical thinking skills to build a diagnostic process around the limited PID information you do have.
This is not always easy but once you get the hang of it, you will realise that in some cases, one piece of PID information can be just as valuable as a laundry list of symptoms are.
