Diagnostic Aids

When 2 or more codes for misfiring cylinder are recorded repeatedly but no random misfire code is recorded, it indicates misfires were detected and recorded at different times. If misfire cannot be reproduced, reason may be because of driving with lack of fuel, improper fuel, fouled spark plug, etc. Using scan tool, read freeze frame data. Freeze frame records engine conditions when malfunction is detected.

If is case that DTC besides misfire is memorized simultaneously, first perform the troubleshooting for them. Read freeze frame data using OBD-II scan tool or hand-held tester. When troubleshooting, it is useful to determine whether the vehicle was running or stopped, the engine was warmed up or not, the air-fuel ratio was lean or rich, etc. at the time of the malfunction. When the vehicle is brought to the workshop and the misfire is not occurred, misfire can be confirmed by reproducing the condition of freeze frame data. Also, after finishing the repair, confirm that there is no misfire. On 6 and 8 cylinder engines, misfiring cylinder identification is disabled at high engine speed and only a general misfire fault code P0300 is stored instead of a cylinder specific misfire fault code (i. e., P0301-P0308).

Under the following conditions, only P0300 code may be stored. Misfire starts in the high engine speed area or misfire occurs only in the high engine speed area. Therefore, when a general misfire fault code (i.e., P0300) is only stored, erase the DTCs with the hand-held tester or OBD-II scan tool. Start the engine and drive the confirmation pattern. See CONFIRMATION DRIVING PATTERN  under DTC P0134 & P0154. Read the value of the misfire ratio for each cylinder (or DTC). Perform the repair correspond to the high misfire ratio cylinder (or the misfiring cylinder indicated by DTC). After completing the repair, confirm no misfire is occurring by driving the confirmation pattern. When either of SHORT FT #1, LONG FT #1, SHORT FT #2 or LONG FT #2 in the freeze frame data is outside the range of +/-20%, there is a possibility that the air-fuel ratio is inclining either to rich (-20% or less) or lean (+20% or more). When COOLANT TEMP in the freeze frame data is less than 176°F (80°C), there is a possibility of misfire only while warmed up. In the case that misfire cannot be reproduced, the reason may be because of the driving with lack of fuel, the use of improper fuel, a stain of the ignition plug, etc.