Michael Thomas, automotive and diesel technician, is the author of the McGraw-Hill textbook "Truck and Trailer Systems."


Speed and also Position Sensor Introduction

There room many areas of the car where the speed of rotation needs to be measured. On electronic engines, speed and engine position are essential to fuel injection timing.

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A vehicle's speed sensors include:

wheel rate (WSS)vehicle rate (VSS)transmission input speed (TIS)transmission output speed (TOS)crankshaft speed and position (CKT)camshaft speed and also position (CMP)

Two types of speed and also position sensors are supplied in today’s vehicles; the permanent magnet generator and the Hall-effect sensor.

The irreversible magnet generator or induction pulse generator is widely supplied for automobile speed sensors, wheel speed sensors, transmission speed sensors and crankshaft rate sensors. The Hall-effect sensor is used as an exact speed and also position sensor because that crankshaft and camshaft position and speed. To perform the best job possible it's ideal to read an introduction of car computer systems.

Truck and Trailer equipment Textbook

PM Generator Operation

A magnet surrounding by a fine cable collects the magnetic currently of force to create an alternating Current (AC). As the ton ring rotates through the column or wheel, the high and low points space closer and also farther far from the magnet. As soon as the surface ar is closer, a magnetic ar is in ~ its strongest. Together the high point moves away, that distorts (bends) the lines of force across the magnet. Together the currently of force cross the fine wire, AC existing is produced.

External Flywheel ton Ring


This tone ring and also crankshaft place sensor are situate behind the flywheel. The vast notch signal a provided engine position.

Permanent Magnet Generators Testing

A an excellent DVOM will be required to accurately test the resistance and also AC calculation of the sensor. Irreversible Magnet Sensors space a 2 wire sensor. To check the sensor, monitor the procedures below.

Steps for permanent Magnet Sensor Testing

Disconnect the sensor lead.Set the voltmeter come OHMs.Measure the resistance of the sensor across the 2 pins.Check versus the manufacturers specifications. Commonly 600 come 3,000Ω.Check the stamin of the magnet by picking up a large paper clip. If the magnet is cracked inside the sensor, the magnetic ar will it is in weak.To examine the sensor output, revolve the DVOM to AC Volts.Rotate the wheel or every little thing speed you space measuring.Place the meter leads throughout the sensor and measure the AC voltage output.Typically, if the shaft is rotated at about one rotate every 2 secs the output need to be about .7 come 1.0 Volts AC.If the sensor overcome the tests but still has a problem in the circuit, retest at the computer. Use the wiring chart to find the pins to test at the computer. Utilizing a T-pin, carefully slide the T-pin right into the signal wire connection.If the wiring has actually a problem, girlfriend may need to replace the harness.Clear the trouble codes, road test and also recheck to confirm the trouble is fixed.

Service Tip: never ever repair the leads coming away from a permanent Magnet sensor. This wiring has a shield constructed in to defend the signal from radio or magnetic interference. Another an approach of shielding the signal is come twist the pair of wires.

Permanent Magnet Sensor Test


Two tests are accessible for two wire permanent Magnet Sensors. AC voltage output and resistance (Ohm's) tests.

Permanent Magnet Sensor Problems

The pm Generator format speed sensor produces a really low AC voltage. This voltage would be really easy to have external interference influence the signal. The loss or interference of the signal can cause; the engine to protect against running, the ABS come not work or the speedometer come quit working.To safeguard the signal, the wires room shielded or twisted to alleviate the interference. The wheel speed sensor harnesses generally have shielding constructed into the harness and should not be repaired only replaced. Twisted wires must be preserved twisted as one cable acts favor the shield to the other.

Clearances have the right to be an issue between the ton ring and also the sensor magnet. Too much clearance and the magnetic field will be weakened. Too tiny clearance and the sensor could be damaged by the tone ring to mark the sensor.

Damage come the sensor magnet might occur if the sensor to be hammered top top or even just dropped. This might crack the magnet in the sensor i m sorry would result in small or no output.

The wiring and also connectors might be damaged or corroded. Due to the fact that this type of sensor produces such a low voltage, a bad connection voltage drop could significantly affect the sensor reading.

Hall impact Sensor Signal and Voltage Test


As the engine or ingredient is rotated, the signal should go High and also Low as the ton ring (windows) pass.


Hall effect Sensor Testing

To test a Hall result Sensor you will certainly need precise DC Voltmeter collection to the 20 Volt scale.

With the sensor plugged in insert a T-pin in the signal cable cavity that the sensor plug.Bar the engine end or turn the tower the sensor is sensing.Watch the voltmeter.As that rotates the signal voltage must go ago and soon from short voltage to the stated voltage sent to the sensor. Some Crankshaft and Camshaft ton Wheels have actually an odd Notch to signal an engine position.If over there is no signal, unplug the sensor and check for resource voltage at the connector.Check the floor by powering one meter lead and also testing because that ground v the other.If the power and also ground space good, replace the sensor.If the sensor has actually a exactly high/low signal but still has actually a code, use the wiring diagram to determine the Hall effect sensor signal cable at the computer. Retest because that the signal. If over there is no signal, fix the harness. If there is a signal at this suggest but no point out of a signal indigenous the computer, the computer system is bad.Repair the problem and also check to view if that works.Clear the problem codes, road test and recheck to check the trouble is fixed.

Service Tip: When trial and error a Hall impact Sensor with 5 Volt supply, hook a DC Voltmeter to the signal cable at the video camer or Crank sensor. Bar the engine over and also watch the meter. The meter will read 0 climate 5 volts DC together the engine is turned.

Hall result Sensor Problems

Because the Hall impact Sensor reports the position and speed of the component, ns of the signal might cause; the engine to avoid running or the speedometer come quit working. Many of these troubles will additionally show up as a "Trouble Code" save on computer in the computer system system.

One the the difficulties that may develop is a clearance problem. The sensor need to be in ~ a stated clearance come the tone ring the reads. Frequently this clearance is around .020 to .040". Part sensors are adjustable, when others room not. Some flexible sensors use shims and also others may screw right into the housing. The crankshaft and also camshaft position sensors that space sealed through an O-ring should never have silicone sealer applied as this have the right to act prefer a shim.

Wiring and connection problems can occur due to the routing and also condition the the harness. The connectors space designed to be weather chop to store out dirt and also moisture. If the seal because that the connector is damaged or missing, moisture could cause a corrosion problem. A bad connection may cause an intermittent bad connection to collection up the problem. Test and also repair the difficulty using the factory recommended procedures for the finest results.

This write-up is accurate and also true to the ideal of the author’s knowledge. Contents is because that informational or entertainment purposes only and also does not substitute for personal counsel or experienced advice in business, financial, legal, or technological matters.

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Jim Maye on august 12, 2020:

This website is very informative.

It has actually helped me rather a bit and is a should for others when they have concerns with car or truck engines not functioning correctly