I have a P0136 on my 1998 4Runner 2.7 3RZ-FE. It uses both narrow band sensors (pre cat and post cat) Looking at the waveform of the post cat sensor, often upon acceleration it drops to 0 volts. Common sense suggests that the pre cat sensor waveform should fluctuate as the mixture is cycling from reach to lean and the post cat should remain steady (if cat is working) but should it drop to 0 volts? ST fuel trim is about 3% whilst LT is -10.9%, I’m wondering if I’m dealing with a faulty sensor.. I used the Toyota Techstream since it doesn’t have a very good recording function I had to physically film the data, here’s a video of a short drive at operating temperature: Blue trace is pre cat sensor Green is post cat sensor Red is RPM Yellow is vehicle speed


I’ll appreciate any input.


P0136 indicates that the exhaust is running too lean. When the voltage on a 02 sensor is high it is running rich, low voltage is running lean.

Most of the time P0136 indicates a defective sensor or a leak in the air intake system.

If it is same thing that happened to me (the air leak one) check the rubber pipe between the air filter assembly and the intake manifold. I had 2 2" cracks in the rubber which caused a drop in the volume of air entering the intake manifold. Mechanic had to seriously clean the throttle body and the MAF sensor element and then reprogram the ECM after replacing a new ribber pipe.

  • P0136 for Toyota indicates a circuit malfunction, no necessarily a low voltage. It sounds like your mechanic doesn’t really know about ECM reprogramming, to reset the fuel trim you can pull the EFI fuse- no reprogramming necessary (if you indeed have a Toyota). Thanks for your input – Rob May 18 at 13:10

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