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Common principles of diagnostic with FORScan

Posted: Tue Sep 20, 2016 4:50 pm
by FORScan
In contrast to majority of OBDII applications, FORScan is designed to use service level abilities, like a professional equipment. It means that FORScan operator must have at least some basic knowledge of troubleshooting principles in order to use it effectively. This article is written for people that have no these skills yet but looking for a start point.

In simple case, the troubleshooting sequence is:

Step 1. Connect to vehicle
Step 2. Check for diagnostic trouble codes (DTC). If there is no any code related to the problem, go to Step 6.
Step 3. Analyze the DTC code(s) found.
If the DTC description provided by FORScan doesn’t contain enough information, go to Step 5.
Step 4. Fix the problem. End.
Step 5. Obtain additional information using FORScan datalogger (read PIDs). If information is enough, go to Step 4.
Step 6. Try to get more information using a workshop manual for the vehicle, if it is available. The workshop manual may contain a lot of helpful information, including pinpoint tests and diagnostic charts.
Step 7. Try to learn other users’ experience (can be found using Google by DTC or problem description).

As you may see, read and analysis of diagnostic trouble codes is the first thing that has to be done. So it is important to understand what DTC is and how it works. Generally speaking, if a module finds an issue, it throws a diagnostic trouble code so a technician can read it and realize the issue exists. The priority of the issue may vary in range from not really important (rather some kind of warning) to crucial. In the last case the module lights its malfunction indicator lamp (MIL) up so the issue becomes visible for the driver. Otherwise, if the issue is not important enough, the driver will not see it until next visit to a workshop.

In Ford/Mazda diagnostic, there are 2 kind of codes: Continuous Monitoring (CM) and On Demand (OD). CM codes are thrown by a module if it detects an issue during its regular work . Operator doesn’t need to perform any action to generate these codes, but just read them from the module memory. OD codes are generated during a self-test (on demand test) called by operator. Self-test/OD codes are helpful in case of malfunction that cannot be detected without operator’s assistance. For example, BCM/GEM module usually has no ability to detect door ajar switch malfunction as when the door is closed, the switch circuit is normally broken. So the module cannot recognize if the door is closed, or the switch is damaged. In order to find this out, operator has to run the module self-test with all doors opened. If any switch is broken, the corresponding OD code will be thrown.

Format and information, provided in DTC, depends on module. We conditionally divide the ECUs into 3 groups:
- App. 1994-2003 – provide no malfunction sub-code and status info (except standard OBDII codes that may have Confirmed or Pending status). Instead of, the DTC descriptions usually pretty detailed and informative.
- App. 2004-2008 – provide minimum of sub-code and status info, but also quite detailed description.
- App. 2009-now – provide informative sub-code and status code, but usually very short description, as designed to be used in conjunction with technical database that explains the issue (workshop manual, Ford ETIS etc).

Let’s review a real example of diagnostic session:

Ford Ecosport Europe 2014, less than 2 years old, 11700 km. Unstable start of engine(after 2-3 attempts). ABS, TCM, EPS malfunction lamps light up right after the start and SYNC asks to visit a workshop urgently. Car owner is in panic. After connecting FORScan a lot of diagnostic trouble codes were read. Although this may look like a serious global trouble, or even multiple troubles, brief analysis shows that almost all of these codes indicate low/unstable power voltage:
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Considering that multiple modules report approximately the same, the only explanation is that the battery died. To confirm, read VPWR PID in PCM module in KOEO and KOER mode. It shows 10.5 in KOEO mode (that’s too low – should be around 12) and 14.5 in KOER mode (that’s normal and means the alternator/charging are most likely fine)

So our conclusion was that the battery is dead (bank short circuit).

Interesting thing is that this car didn’t show typical signs of dead battery – starter worked and engine ran even at very low voltage, just a bit slower than usually. When the voltage fell below some threshold, starter was simply blocked. The car owner can’t believe the brand new firm Ford battery died for less than 2 years of accurate use, so he decided to visit a dealership in hope it will be resolved in bounds of warranty. Unfortunately, he was wrong – dealer’s diagnosis was the same: battery died because of constant undercharging (caused by small mileage - work in permantent start-stop city conditions) , not covered by warranty. So the owner had to pay not only for the new battery, but also for the dealership diagnostics.

Finally, 2 more screenshots that illustrate what are the sub-code (Additional Fault Symptom) and Status and how FORScan displays them:
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5.jpg (104.65 KiB) Viewed 53455 times

Re: Common principles of diagnostic with FORScan

Posted: Sun Jan 12, 2020 9:48 pm
by Clyde
Thank you for posting this information! I am a brand new beginning user of Forscan brought to the program through research in looking for solutions for programming key fob for my truck and have been amazed at all of the functionality of this program!
Amazed and more than a little intimidated by it since I would hate to cause myself more headaches and bigger repair bills should I make a mistake.

Re: Common principles of diagnostic with FORScan

Posted: Wed Sep 09, 2020 5:23 pm
by FranTheMan
Good information and a great base for noobs.

Re: Common principles of diagnostic with FORScan

Posted: Fri Oct 09, 2020 1:04 am
by Boof
Should have read this properly the first time. It would have saved me a few thinkaches :shock:

Re: Common principles of diagnostic with FORScan

Posted: Sun Nov 22, 2020 12:41 pm
by Mayrin01
Gracias por la informacion. Estoy en Venezuela y tenia dudas si el programa funcionaba con vehiculos fabricados en mi pais. Acabo de instalarlo en mi computadora y adquiri el ODBLINK EX y ya lo estrene con mi camion Ford F-350 Superduty 6.2 del año 2013 y estoy viendo codigos que mis otros dos escaner no monitoreaban(Foxwell y Blue Driver). Con la informacion publicada en este apartado podre comprender mejor las fallas que mi camion esta presentando. Muchisimas gracias.