Diagnostic Aids

WARNING: This page is about a different car, the 2003 Lexus SC 430. However, it is still accessible from the selected car via links, so may be relevant.

If any DTCs besides misfire are present, first perform the troubleshooting for other DTCs. Read freeze frame data using hand-held tester or OBD-II scan tool, as freeze frame data records the engine conditions when a malfunction is detected. When troubleshooting, it is useful for determining whether the vehicle was running or stopped, the engine was warmed up or not, the air-fuel ratio was lean or rich, at the time of the malfunction. If the misfire does not occur when the vehicle is brought to the workshop, the misfire can be confirmed by reproducing the condition of the freeze frame data. Also, after finishing the repair, confirm 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 (P0301-P0308). Under the following conditions, only P0300 code may be stored. Misfire starts in the high engine speed area or occurs only in the high engine speed area. Therefore, when a general misfire fault code (P0300) is only stored, erase the DTCs after reading freeze frame data with the hand-held tester or OBD-II scan tool. Start engine and drive the confirmation test drive. See CONFIRMATION DRIVING PATTERN and read value of misfire ratio for each cylinder (or DTC). Perform the repair corresponding 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 SHORT FT #1, LONG FT #1, SHORT FT #2 or LONG FT #2 in the freeze frame data is over the range of 0-40 percent, there is a possibility that the air-fuel ratio is inclining either to RICH (-20 percent or less) or LEAN (20 percent or more). When COOLANT TEMP in freeze frame data is less than 176°F (80°C), there is a possibility of misfire only during warm up. If misfire cannot be reproduced, the reason may be due to driving the vehicle with lack of fuel, use of improper fuel, a stain on the ignition plug, etc.