Mechanics

TOYOTA TACOMA SENSOR PROBLEM

2000 Toyota Tacoma • 275,000 miles

Having intermittent electrical issues and have narrowed it down to the terminal wire connection at the ECM for the common ground to the TPS, VPS, MAF, etc. Truck starts but if terminal wire is moved then error codes appear or it stalls. Some error codes are triggered at initial start, but sensor tests fine at investigation. Common ground is the E2 at the ECM and the terminal housing is the E6 connector. Have replaced terminal wire and housing with certified parts from a dealership. Have tested for continuity at sensors and tested ECM and both test fine. Any thoughts or information is much appreciated.

Thank you,
Brad Cox
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January 7, 2013.



Without actually seeing how you're doing the tests, I can make some generalizations to get you started. Since the TPS is usually the easiest one to get to, measure its three voltages. Normal is a 5.0 volt feed, 0.2 volts on the ground wire, and 0.5 to 4.5 volts on the signal wire, depending on throttle position. That signal voltage range is approximate. If you find 0.3 to 3.8 volts for example, that's fine. The point is it has mechanical stops to prevent it from going all the way to 0.0 or 5.0 volts. Those two voltages trigger fault codes. With an open ground wire you will find 5.0 volts on all three terminals. By the way, those readings must be taken with the sensor plugged in, not disconnected.

If you do find 5.0 volts on the ground wire you need to do the same tests on those other sensors that share a common ground wire, but it sounds like you did that already. That will tell you whether the break is in the wire for just one sensor or it's in a part they all have in common. Given that you have three codes at the same time, that says the problem is in a part they all have in common.

Next is to measure that voltage at the computer. It sounds like that's where you think was the bad connection and you replaced that terminal, but that circuit actually goes THROUGH the computer's circuitry, then to ground on one of the computer's ground wires. Those are the ones you need to check. There will always be at least two ground wires, and often there's four. The "signal" ground wire is for small-current items like those sensors. The "power" ground wires are for high-power devices like injectors, ignition coils, and relays. If both circuits shared a single ground wire, a very tiny amount of resistance in the wire or its connection would result in a voltage drop pulsing in time with the current flow that's pulsing in the injectors and coils. Those voltage drops are insignificant to those circuits but are a real big deal to sensor readings. That's why they use different ground wires.

On some cars, two signal ground wires are just in parallel so if one is cut, the other one still works. On some cars the two ground wires are for different sensors and both have to be working. Measure the voltages on all of the ground wires.

One more point to be aware of is you can not run a new ground wire from the sensors to the engine block or body. That 0.2 volts I mentioned earlier on the ground wire is proof that the computer is seeing current flow through it and it knows it's okay. It will set a fault code if it sees 0.0 volts on that wire.

Caradiodoc
Jan 8, 2013.