General OBDII Service Tips

^ Always Record Freeze Frame Data Before Clearing DTCs: The FFD is a valuable tool for identifying engine operating conditions present when a DTC set. This will help you verify a vehicle concern and validate your repair attempt.

^ Reset KAM After Repairs: After at repair involving clearing DTCs, always clear the KAM. The KAM holds memory of specific vehicle operating conditions used for its adaptive strategies. If the KAM is not cleared the PCM may remember operating conditions present before your repairs.

^ Diagnosing Multiple DTCs With Similar Meanings: When paired DTC's with similar descriptions for HO2S concerns are set (P01351 P0155), (P01411 P0161), (P11311 P1151), (P11321 P1152) it is unlikely that replacement of the HO2S will correct the concern.





Example: A vehicle with a MIL concern indicating KOER DTCs (P01351 P0155) both front HO2S heater circuit failure codes and no other DTCs set. The most likely cause of this concern would be something common to both heater circuits such as the heater power supply. Always review the wiring diagrams to find circuits common to both sensors. In the the figure shown, splice A would be a good place to start your inspection.





^ NGS & WDS HO2S PIDS With 0 Values: NGS and WDS may display PIDS for more HO2S than a vehicle is equipped with. If the scan-tool shows a value of 0 for an HO2S PID, it may not have that HO2S. The NGS figure shows a 4-cylinder engine with PIDS for two upstream and two down-stream HO2S and the unused HO2S show 0.0 volts.

^ HO2S Measure Oxygen Content Not Unburned Fuel: Misfires result in lean HO2S readings. When a cylinder misfires, raw fuel and oxygen are passed into the exhaust. This additional air makes the exhaust lean. For an HO2S to indicate a rich condition, the fuel would have to burn in the combustion chamber along with the oxygen.