Summary
The objective of this procedure is to show you how to retrieve, record and clear stored OBD I & II diagnostic trouble codes using a scan tool. Remember, when retrieving codes for an OBD I vehicle, clear the codes then start the vehicle and recheck for any codes that reset. When diagnosing and OBD II vehicle, do not clear the codes until the vehicle is repaired.
Part 1. Preparation and safety
Objective
- Retrieve, record and clear stored OBD I & II diagnostic trouble codes using a scan tool.
Personal safety
Whenever you perform a task in the workshop you must use personal protective clothing and equipment that is appropriate for the task and which conforms to your local safety regulations and policies. Among other items, this may include:
- Work clothing - such as coveralls and steel-capped footwear
- Eye protection - such as safety glasses and face masks
- Ear protection - such as earmuffs and earplugs
- Hand protection - such as rubber gloves and barrier cream
- Respiratory equipment - such as face masks and valved respirators
If you are not certain what is appropriate or required, ask your supervisor.
Safety check
- If the vehicle is to be run inside the workshop use exhaust extraction hoses.
- Output solenoids can be energized from the scan tool, activating components without warning. It is imperative that the operator should follow the service manual procedures.
- Make sure that you understand and observe all legislative and personal safety procedures when carrying out the following tasks. If you are unsure of what these are, ask your supervisor.
Points to note
- Make sure that you follow service manual procedures for the vehicle you are working on.
- The standard procedure for retrieving codes for an OBD I vehicle, is to access the codes, write them down, clear the codes, start the vehicle and recheck for any codes that reset.
- The standard procedure for diagnosing an OBD II vehicle is different as it requires that the codes should NOT be cleared until the vehicle is repaired. Clearing the codes also clears all of the freeze frame data in the system that is useful for the diagnosis process.
- It may take several 'trips' for the code to reset, so with OBDII you must complete the diagnosis process first before clearing the codes.
- Always check for any applicable service bulletins when diagnosing computer related problems, as they can provide valuable information about new faults that emerge on vehicles as their operational characteristics change as the vehicles get older.
Part 2: Step-by-step instruction
- Connect the scan tool
Locate the scan tool access point and connect the scan tool using the appropriate connector for the vehicle. Turn on the vehicle ignition. Turn on the scan tool. Run the scan tool diagnostic program and navigate through each of the different systems in turn to access the diagnostic trouble codes from the vehicles electronic control module. Note your findings for each vehicle system.
- Check your findings
Look up what each code means and present the information to your supervisor. Any fault indicated by the diagnostic trouble codes will need to be corrected before you clear the codes.
- Clear fault codes
To clear the fault codes from the vehicle, select the delete codes option on the scan tool. Check that the codes have cleared, and turn off the vehicle ignition.
- Recheck for fault codes
Turn on the vehicle ignition. Run the scan tool diagnostic program and navigate through each system again to check the codes do not reactivate. If the fault codes reactivate, take your findings to your supervisor. Turn off the vehicle ignition. Turn off the scan tool and disconnect from the access point.
