Great Information, But Not Diagnosis
The FIXD and HUM devices are popular tools promoted as ways to save money on car repairs. They read diagnostic codes when warning lights illuminate or performance issues arise. However, these devices provide codes and basic explanations, not actual diagnoses. "These codes are not a diagnosis, it is a direction or starting point to work towards a diagnosis."
A proper automotive diagnosis requires a methodical process:
- Identify and duplicate the problem
- Scan for diagnostic trouble codes and record freeze-frame data
- Perform pinpoint testing of all system components
- Test modules, wiring, power, and grounds
- Analyze results against engine computer data
- Test theories to determine root cause
- Make repair recommendations
- Retest after repair to verify functionality
Providing Information is Different than Testing
These plug-in devices only retrieve codes and suggest probable repairs without conducting actual testing. While helpful for understanding urgency, guessing at repairs without proper diagnosis costs significantly more.
For example, an exhaust leak might trigger oxygen sensor codes, but replacing sensors (up to 8 on newer vehicles) wastes money. Fixing the leak resolves the underlying issue.
You Still Need a Proper Diagnosis
"A properly maintained and when there is a problem a properly diagnosed car will always be more economical than guessing."