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Code set parameters are a critical component of accurate diagnostics

Friday, June 1, 2018 - 06:00
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This article will review what code set parameters are, as well as how they can be used as part of the diagnostic process. The information included in those parameters should also be part of the repair validation to help ensure the vehicle is repaired right the first time. Ideally, the customer should not be a part of your repair validation process.   

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All diagnostic trouble codes are triggered because something went wrong. I know that seems like an obvious statement, but it’s the rules used to determine that something went wrong that are important for diagnostics. Those rules are what are known as code set parameters. I’m sure you know a technician who has pulled a vehicle into the bay, scanned it to see what codes were present, and then cleared them to see which one(s) came back as part of their diagnosis (or maybe you do that yourself). Hopefully before the “clear all” function was chosen, the codes that were present were documented. Even if they were documented though, what is the purpose of going through that process? The most common reason I’ve heard is to determine which of the codes they should chase when there are multiple codes. I would argue that code set parameters are a much better (and more accurate) way of doing the same thing, and hopefully you will too after reading this article (if you don’t already agree). 

Can you answer these questions using the data provided along with service information you have available? The answers can be found at the end of this article.

Code set parameters include information such as, but not limited to:      

  • Conditions required for the code to set
    • Minimum or maximum engine temperature 
    • Engine load conditions
    • Fuel tank level 
  • Interaction with other codes/tests
    • Codes that may trigger with it and which is the “primary” 
    • Tests that are disabled when the code is set 
    • Codes that can’t be present for this code to set
  • Data ranges that will cause the code to set
    • What is acceptable/normal 
    • What will exceed that limit and trigger the code 
  • Monitor Strategies
    • Frequency of test being run
      • Continuous monitor 
      • Once per trip 
    • Frequency of failure required to trigger the MIL/Code 
    • One-trip code (sets immediately upon failure) 
    • Two-trip code (sets after two failures within a given time frame) 
    • Required sensors/components

Building your diagnostic process 

So how can this data be helpful in a diagnostic process? To start with, honestly ask yourself if you have a diagnostic process that you are using. The basic definition I’ve used in the past for a diagnostic process is simply a series of steps used to locate the source of a problem. That’s a broad definition and realistically, the method used by each technician is likely to be somewhat different. If you haven’t thought about your diagnostic process, I’d recommend taking a few minutes to write it out step by step. Does it include some of the following steps? These are the steps that I’ve taught over the years that I feel are a good starting point to build a diagnostic foundation. 

1. Gather information from the owner and/or driver of the vehicle. (This is typically gathered by a good service advisor, but technicians need to keep them accountable to get the data.) 

  1. When did the problem start? 
  2. Did they notice any performance changes? 
  3. Has any other work been done recently to the vehicle? 

2. Scan check the vehicle. (This should include documenting any codes, current or pending, and related freeze-frame data, if available.) 

  1. May turn up codes beyond the initial complaint (related or unrelated) that could prove important 
  2. Freeze-frame data may help you determine how to duplicate the problem. 
  3. Documents the condition of the vehicle BEFORE you start working on it to help prevent the “ever since you” discussions after you return the customer’s vehicle 
  4. Verify the monitors have all run to be sure your repairs don’t allow the vehicle to start running a test that hasn’t been run for a long time, which may turn the check engine light back on shortly after it leaves your shop. 

3. Research information related to the concern. 

  1. Check for relevant TSBs, open campaigns and/or recalls. 
  2. Check the service information related to any codes, including the code set conditions (parameters) 

4. Attempt to duplicate the problem. 

  1. Requires the vehicle to be operated under the right conditions 
  2. If you can’t duplicate the problem, do you continue? 
  3. If you can’t duplicate it, can you accurately validate your repair?

5. Don’t get tunnel vision. 

  1. Pay attention to the entire vehicle while test driving.
    1. The customer concern may be caused by something related that they haven’t even noticed (for instance, a check engine light caused by a leaking exhaust.) 

6. Define when/how the problem occurs. 

  1. Provided you can duplicate the problem, make notes related to:
    1. Load 
    2. Speed (engine and/or vehicle) 
    3. Temperature 

7. Perform a visual inspection looking for things like: 

  1. Signs of previous work 
  2. Accident damage 
  3. Loose/broken parts 
  4. Leaks 

8. Narrow the problem down as needed. 

  1. If multiple codes are present which one should you diagnose first? 
  2. Attempt to eliminate potential causes of the problem one at a time.
    1. Changing more than one thing at a time can cause confusion 
    2. Typically start with the easiest item to eliminate as a potential cause, then work toward the ones that are more difficult to rule out.
      1. Note – if you have access to third-party information sources that help determine frequency of various failures, you may want to start by testing the most common failure first, even if it’s not the easiest one to test. 
  3. Continue testing until you’re relatively confident you’ve found the root cause. 
  1. Verify your diagnosis.
    1. If possible, bypass what you think is the root cause to see if everything works properly. 
    2. Replace the suspected failed part with a “known good.” (I’m not a fan of this one!)
      1. Be careful; if the part you substitute with a known-good one wasn’t the root cause, you could potentially damage it as well 
  1. Perform the repair.  
  1. Validate your repair. 
    1. Be sure to operate the vehicle under the conditions that allowed you to duplicate it previously 
    2. Don’t rely on the check engine light to verify your repair.
      1. Utilize your scan tool and the information you already know related to what conditions must be met for the codes to set.

I know that seems like a long list of things to do, but realistically most of the steps don’t take that much time to complete. It is critical that you have access to good diagnostic tools and good service information. If you can’t trust one or both of those that you have access to, you are starting out behind in the diagnostic game and are likely to end up losing too often. There are a lot of good resources and tools out there including those available directly from the OEM. If you are using aftermarket diagnostic tools, I recommend having more than one, and they should be from different manufacturers. With two different scan tools at your disposal, if you have something displaying on your scan tool that doesn’t make sense, you have a way to double check it.   

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