Abs sensor location
Actually, the brake system HAS indicated a problem -- that's exactly what the ABS warning lamp is doing! Unfortunately, the very nature of the ABS system means that you will not usually notice a system performance problem until it's too late -- that is, until you need the system to work and it doesn't!
There is not just one ABS sensor -- in fact, in most cases, there are four. Also, the fact that the warning light is on does not necessarily mean that a sensor has failed -- it just means that the system has stopped working properly and/or has failed its self test. The problem could be as simple as a sensor or exciter ring/trigger wheel, or it could be a wiring harness, modulator, or ECM issue.
Generally, unless something has struck or disturbed a sensor or exciter ring/trigger wheel, they are normally not high-failure items.
Typically, an ABS system monitors the rotational speed of each wheel and reports that speed to the ECM. The ECM compares the speeds of all of the wheels during braking, and if it finds that one (or more) of the wheels is not rotating while the others are, it modulates the brake pressure to the stopped wheel(s) as a means of breaking the skid and getting the wheel(s) turning again.
The wheel speed measurement is accomplished via a sensor positioned in close proximity to a toothed wheel called an exciter ring or a trigger wheel at each vehicle wheel position. Sometimes, the exciter ring is machined into the inboard face of the brake rotor, drum or hub. In others, it may be pressed onto a shoulder on the axle shaft. Regardless of its actual implementation, there is a calibrated fixed distance between the exciter ring and the face of the sensor when both are properly installed.
The sensor itself is effectively a coil of wire wrapped around a magnet (either a permanent magnet or an electromagnet). As the exciter ring turns, its teeth and gaps alternately pass the core of the sensor and influence the magnetic flux field surrounding the sensor's coil. This alternating rise and fall of the flux induces an AC signal in the sensor coil, which is the signal monitored by the ECM. The frequency of the AC signal is proportional to the wheel speed.
Some of the things that can disrupt proper wheel sensor operation are impact damage to a sensor, to its cable harness, or to its exciter ring, filling (or partial filling) of the exciter ring tooth gaps with ferrous material such as brake drum or rotor filings, and, of course, physical damage due to improper service operations.
Has any repair or maintenance work been done on the vehicle shortly prior to the problem appearing?
Oct 04, 2012 |
2000 Chevrolet Impala