- Thermistor.
- Pulse generator.
- Variable-capacitance pressure sensor.
- Piezo-resistive pressure sensor.
- Potentiometer.
Test procedures vary for these sensors as they operate on different principles, but the similarities all these sensors share is that they are designed to send a voltage signal back to the ECM to let it determine engine operating conditions. This information can then be used to adjust output parameters such as fuel injection timing, or used as fault detection for driver warning systems.
We also broke out the scan tool and used it to help test these sensors. A multimeter works just as well, but a scan tool can be faster and easier. For instance, we hooked up a gauge and pressure booster to the manifold boost pressure sensor, and with it connected to the ECM and the scan tool hooked up to the truck, we were able to match boost pressure in PSI on the pressure gauge and on the scan tool. This tells us the sensor is good and working as intended.
This could also be done with a multimeter, but would specifications telling us how to interpret voltage readings to a corresponding pressure value.
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| Applying pressure to the manifold boost pressure sensor with our pressure gauge. |
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| Scan tool data from the ECM match our pressure gauge readings, indicating that the sensor is working as intended. |
My reflection:
Not all these tests went flawlessly. We had some technical difficulties involving a crankshaft position sensor, which would not produce voltage when a magnet or piece of metal was passed across it, and a throttle position sensor which gave us readings in reverse of what we expected from specifications. We will likely be revisiting these next class.
The question I might raise then is how would a technician in the field deal with these technical difficulties? How would their methods differ from ours? Did we perhaps make a mistake in our tests, or is there an actual technical problem with the sensors, electrical systems, or tools we were using to test them?
Erik, good post! Could be an error on my behalf? Here is a test using DDDL software:
ReplyDelete0.2.4 Check Timing Reference Sensor Status
Perform the following steps to check the TRS status via a r/min readout:
1. Select engine speed and active codes on the DDR.
2. Crank the engine for ten seconds while observing DDR display. A battery voltage surge
while cranking with electric starters may blank or reset the DDR.
[a] If the display reads greater than or equal to 60 r/min, refer to section 10.2.9.
[b] If the display reads less than 60 r/min or constantly reads 60 r/min,
refer to section 10.2.5.
[c] If code 41 is displayed, refer to section 41.3.1.
[d] If code 42 is displayed, refer to section 42.3.1.
The TRS sends a signal to the ECM. This signal is generated by a series of evenly spaced teeth on the timing wheel. As the timing wheel rotates with the crankshaft, a tooth passes by the TRS. These signals are used by the ECM to determine injector solenoid operation times and engine speed.
Erik, check this link out:
ReplyDeletehttps://calderondieselblog.wordpress.com/2017/03/13/capstone-research-project/
Wow! He is one of the Bellingham students.