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Where does 5V reference come from?
The 5V reference wire was the first wire in the harness to be grounded. Keep in mind that the ECM/PCM also needs the 5V to operate and it lost power as well.
How do you check voltage on a sensor?
To test if the sensor is receiving power, set your DVOM to 20V DC. Unplug the sensor and connect the meter probes to the harness terminals- the negative to GND and the positive to B+. The meter reading should indicate a value close to the battery voltage or from between 10 to 13 volts.
How do you check ECM?
The least invasive way to diagnose your ECM is to connect an onboard diagnostic (OBD or OBD II) tool to the diagnostic port. From there, you can scan to see if your engine computers have produced any error codes. There are many of these codes, and your diagnostic tool’s manual should have information on what they mean.
What does a 5 volt reference signal mean?
Photo 2: The ECT sensor consists of a 5-volt reference, a variable thermistor, and a signal return wire to the ECM. As you might suspect, this was a no-code problem that had bewildered two previous shops. If I recall, one shop replaced the idle air control (IAC) and another replaced the oxygen sensor because the exhaust “smelled rich.”
Where to test for a 5V reference circuit problem?
The easiest place to start testing is at one of the engine sensors (MAP, TPS, etc.). When you confirm that the 5V reference circuit is dead, you need to locate the source of the problem.
What is the 5V reference circuit voltage drop?
If the 5V reference circuit (in-series) limiting resistor, for example, is 50 ohms and the sensor is 25,000 ohms, then the amperage would be .000199A, or 199µA. The clamp-on amp meter will not be able to measure amperage that low. Also, the voltage drop across the limiting resistor (50 ohms) is around .009V.
What is the 5V reference circuit limiting resistor?
If the 5V reference circuit (in-series) limiting resistor, for example, is 50 ohms and the sensor is 25,000 ohms, then the amperage would be .000199A, or 199µA. The clamp-on amp meter will not be able to measure amperage that low.