First let me expand on a few ideas that may be coming into play. There's a lot of different fault codes that can be related to one sensor and they mean different things. They could mean that sensor is working fine but it simply detected a bad operating condition. They can indicate in which way a sensor has failed, but usually it is the entire circuit that must be suspect and diagnosed. Some code readers give the written code description and those are at the mercy of the person who programmed those tools. They can vary enough to cause confusion, ... And they don't explain how to diagnose the code. The best is to get the actual code number so we can find the listing on a chart.
Oxygen sensors have their own way of working so we'll ignore them for now. Most other sensors run on 5.0 volts. Their output signals are one of two forms; a solid voltage or a square wave signal. In a square wave the voltage in this case would go from 0.0 volts to 5.0 volts, and back again many times per second, like flipping a switch on and off very quickly. Some signals go on half the time and off half the time but how rapidly that happens can change. That is called changing the "frequency". Some maintain a steady frequency but the length of the on-time and / or off-time can change. That's called "duty cycle". By far the easiest to understand is the throttle position sensor. It puts out a steady voltage that varies based on how far you push the gas pedal.
The throttle position sensor is a long carbon resistor. A ground wire is attached to one end and the 5.0 volt feed wire is attached to the other end. If you measured in the middle you'd find 2.5 volts. That's the secret to how they work. A movable contact runs along that resistor that is attached to the throttle blade. As you push the gas pedal more, the movable contact moves closer to the 5.0 volt feed terminal so the voltage it reads goes up. To simplify it, as you run the throttle from fully closed to fully open the voltage on the signal wire will go from 0.0 volts to 5.0 volts. That's how volume controls worked in older tvs and radios.
The secret to detecting problems that set fault codes comes from adding another detail. The sensors are designed with mechanical stops that only allow them to go down to 0.5 volts and up to 4.5 volts. Every sensor is different and you might find a range of 0.4 to 4.2 volts, for example. The point is it will never reach 0.0 or 5.0 volts.
If there is a break in the 5.0 volt feed wire going to the sensor, or a break inside the sensor, there would be no voltage anywhere in it, including coming out on the signal wire. You'd have 0.0 volts all the time which is not an acceptable condition. In my story where 0.5 to 4.5 volts is normal and acceptable, 0.0 volts would be detected as a problem and the code "throttle position sensor voltage too low" would be set. Notice that code doesn't say the sensor is bad. It just tells you which circuit to diagnose, and what the unacceptable condition was.
You have the opposite code. When there's a break in the ground wire or in the sensor, 5.0 volts will be found everywhere including on the signal wire. Since that's more than 4.5 volts, the code "throttle position sensor voltage too high" will be set. That has nothing whatever to do with the car's electrical system that should be running between 13.75 and 14.75 volts. That has everything to do with that 5.0 volt supply voltage which comes from the Engine Computer and is very carefully regulated. You won't find that varying by more than a few hundredths of a volt.
Think of that throttle position sensor as being two parts split right where that movable contact touches the resistor. Your coolant temperature sensor works exactly the same way with two exceptions. First, the sensor is a real simple electronic sensor, not a mechanical device like the throttle position sensor. Second, half of it is inside the computer. That's why the TPS has three wires and the coolant temperature sensor only has two wires. You can still measure the voltage on the signal wire and see it change as the engine warms up. The other wire is the ground wire. The 5.0 volt feed wire is inside the computer.
Now we have to bring in another detail. We talked about a broken ground wire and a broken 5.0 volt feed wire, but the signal wire could also be broken. With no voltage on that wire, it could "float" to some random value just because of all the other circuitry in the computer. To avoid that they add a "pull-up" resistor inside the computer. Under normal conditions that pull-up resistor is so extremely high in value it's like it isn't even there and it has no affect on the circuit. When there's a break in that signal wire though, that's when 5.0 volts appears through it and is detected as that unacceptable condition, and the code "voltage too high" is set. The most common cause of setting that code is unplugging the sensor while the ignition switch is on. The second most common cause is corroded or loose connector terminals, then a break in a wire.
The next thing you should be aware of is that 5.0 volt supply that is produced in the Engine Computer. That is very well protected in case a short circuit occurs. To prevent damage to the internal circuitry the computer will turn it off to protect it. The ignition switch has to be turned off, then back on to reset that power supply. You were wiggling wire harnesses in an attempt to see if the engine would start but if the 5.0 volt supply was shut down already by the computer, no amount of wiggling would have helped until you cycled the ignition switch off and back on.
The last thing is the automatic shutdown (ASD) relay operation. That relay sends current to the ignition coil(s), injectors, alternator field, oxygen sensor heaters, and fuel pump or pump relay. The Engine Computer turns that relay on two times and I think that's what you observed. First, it turns it on for one second each time you turn on the ignition switch. You'll usually hear the hum of the fuel pump for that one second. Next, it turns it on any time it sees engine rotation, (cranking or running). It knows that by the pulses it receives from the crankshaft position sensor and the camshaft position sensor. When either signal is missing, the computer won't turn the ASD relay on during cranking. With no voltage to the ignition coil there will be no spark, and with no voltage to the injectors there won't be any fuel.
Sometimes the computer will set a fault code to tell you which signal is missing. Most commonly the sensor is at fault but the wiring should be checked too. If the 5.0 volts is missing to both sensors, one is usually shorted internally and it killed the supply voltage. You would unplug one or both, cycle the ignition switch to reset the supply, then check again.
Tuesday, August 11th, 2020 AT 6:24 PM
(Merged)
