Diagnostic Aids

WARNING: This page is about a different car, the 2003 Toyota 4Runner. However, it is still accessible from the selected car via links, so may be relevant.

When 2 or more DTCs for misfiring cylinder are recorded repeatedly and DTC P0300 does not exist, it indicates misfires were detected and recorded at different times. If misfire cannot be reproduced, the reason may be because vehicle was driven with a lack of fuel, improper fuel, fouled spark plug or etc. Using Toyota hand-held tester or scan tool, read FREEZE FRAME data. Freeze frame data records engine conditions when malfunction is detected. If COOLANT TEMP displayed in freeze frame data is less than 176°F (80°C), there is a possibility that misfire only exists during warm-up.

If oscilloscope is available, fuel injector operation on misfiring cylinder may be checked by reading the fuel injector signal waveform pattern and fuel injector duration signal waveform pattern which may be checked by connecting oscilloscope between ECM 34-pin connector E4 terminal No. 7 (White/Black wire) and fuel injector driver terminal for misfiring cylinder at ECM with engine idling. ECM 34-pin connector E4 terminal No. 7 is the E01 terminal on ECM. For ECM electrical connector terminal identification, see Figure. For fuel injector driver identification, see IDENTIFYING ECM FUEL INJECTOR DRIVER TERMINALS . ECM is located behind glove box. See Figure. Fuel injector signal waveform pattern and fuel injector duration signal waveform pattern should be properly displayed within proper intervals. See Figure.