Remember, though, that freeze frame data does not record at the exact moment the fault occurred. Freeze frame data might help you uncover a sensor value that is out of normal range only under the conditions that were present when the DTC was set. Be sure you do not erase/clear DTCs since that will also erase/clear freeze frame. The freeze frame data is going to be especially helpful to you in diagnosing these DTCs. It also provides access to freeze frame data and Mode $06 test results if needed. The reason? Generic/Global does not substitute engine values (PIDS). Even if you own the OE scan tool, you should first make use of the Generic/Global mode of the tool. Miss that, and the new converter will quickly suffer the same fate as the old one.Īn often overlooked, but extremely valuable, source of information is the code’s Freeze Frame recording. Even if you do determine that the converter has failed, there is often an underlying reason for that failure. If the PCM interprets the readings to indicate a catalytic converter failure, a P0420 – P0430 pending DTC (Diagnostic Trouble Code) is first set and if the decreased efficiency is still occurring on the next consecutive test, a hard DTC is set and freeze frame data PIDs (Parameter Identifiers) are recorded and stored.Īs with any other diagnostic challenge, you must go after the root cause of these codes using a systematic approach. The PCM programming determines how much zigzagging is acceptable. When this rear sensor voltage zigzags up and down at a steady RPM, it is an indication of a decrease in catalytic efficiency.

But the downstream sensor should sense a relatively stable voltage signal. Conventional oxygen sensors respond to the amount of oxygen in the exhaust stream and provide feedback to the PCM for fuel control. Most vehicles (those certified to OBDII) have both a pre-catalytic (upstream) oxygen sensor (or air fuel sensor) and another oxygen sensor located after at least one of the catalytic converters (downstream). Damaged substrate (broken, clogged, melted) means something killed the cat before its time. Simply stated, its efficiency is a measure of just how well it can do its job.Ī borescope can be used to inspect the condition of the substrate. What is catalyst efficiency? The catalytic converter is the last step in cleaning up any dirty gasses left over after combustion. Other key components involved are the O2 sensor heaters, the O2 sensors themselves, and the Powertrain Control Module (PCM) software that performs the catalytic efficiency testing. But there is more to be considered than the catalytic converters alone. They cover the same problem, with the only difference being to which side of the engine they are referring.

1 codes in the country are the P0420 and P0430 (Catalyst Efficiency Below Threshhold) diagnostic trouble codes.

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