Just joined ATS the other day and I need assistance on my vehicle. It won't start and has no spark and injector signal when I used the noid light tester. Reading ATS database, it looks like a computer failure because it has multiple codes involving the following sensors: mass air flow, intake air temperature, coolant and throttle positioner sensor (TPS). I checked for the power and ground of the ecm terminals at KOEO and all voltage readings were OK. Before I buy a new computer, are there any other stuffs I have to check?
If you look at the yellow wire (vref) of the TPS sensor (located on the top right rear of the engine), it should have 5v at KOEO if you test it with a voltmeter. If not, then it can kill your computer. If it is shorted to the ground like the frame of the vehicle, your reading will be low; if shorted to power, your reading will be high. In shorted circuit situations, the computer will shut itself off to protect itself internally and that is why your vehicle won't start.
To test, unplug each sensor (especially TPS and other sensors with vref wiring) while watching the 5v reading in your voltmeter. You can trace this vref wiring in the wiring diagram and even tell you the color and path of the circuit. The sensor unplugged that will return the normal reading of 5 volts is the one to fix. It could be a defective sensor or bad wiring connected to it. All you do is check the terminals between the sensor and the ecm. If wiring is OK then we know for sure the sensor is no good.
Check this approximate 2003 Toyota RAV4 sensor wirings. Note the red lines which is the 5 volt vref supply and blue lines for ground supplies. Sometimes you can cut the vref supply right at the ecm to test if the ecm is shorted.
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