The HDR system is capable of meeting 'full-range' misfire monitoring requirements on 6- and 8-cylinder engines. The LDR system is capable of meeting the FTP monitoring requirements on most engines, and is capable of meeting 'full-range' misfire monitoring requirements on 4-cylinder engines. There are two different misfire monitoring technologies used: Low Data Rate (LDR) and High Data Rate (HDR). In either a type B or type C misfire, the MIL will come on steady and a code will set as long as the condition occurs on two consecutive trips. For a misfire to be identified as type B, it must be serious enough to raise emissions more than 1.5 times the Federal Test Procedure (FTP) standards.Ī type C misfire is the least severe of the three and indicates that emission levels are high enough for the vehicle to fail an emission test. Types B and C misfires are determined using a 1,000-revolution window and a two-trip monitor. If the percentage of misfires decreases to a point where catalyst damage is no longer imminent, the MIL will stop flashing and remain on steady.

To identify a type 'A' misfire, the diagnostic system counts the percentage of misfires within 200 crankshaft revolutions. In addition, a Diagnostic Trouble Code (DTC) is set and freeze frame data is stored. If detected, the Malfunction Indicator Lamp (MIL) may flash once per second to alert the driver that immediate service is required. The type 'A' misfire is the most serious condition and indicates impending catalyst damage. Each of these misfire types is determined by a percentage of misfires that occur within a specified timeframe and result in specific failure conditions. Depending on the severity, the misfire will be designated as type A, B or C.

OBD II has three different levels of severity concerning engine misfires. If the combustion process does begin but there is a deficiency in one or more of these areas, the combustion process will end prematurely. Unless the fuel mixture is correct, secondary voltage is sufficient and the engine is in good mechanical condition, combustion cannot be initiated. The Powertrain Control Module (PCM) monitors the engine operation for misfires and counts the number of misfires that occur in a specified number of engine revolutions.Īn engine misfire is a condition that results from either a lack of combustion (total misfire) or an instability that occurs during the combustion process (partial misfire). Now, we have OBD II with its misfire detection monitor. If the misfire rate is excessive, the catalytic converter can overheat and be damaged. Misfires generate unburned hydrocarbons and increase the load on the catalytic converter.

It was not all that long ago that a slight random misfire might go undetected.

Misfire monitor profile correction sct x4